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THE TETRODE BOARDS
TM
Control and Protection
for your
Tetrode RF Power Amplifier
All the hard work done!
• Screen supply
• Grid bias
• Tube protection
• TX/RX sequencing
• ALC output
Versatile!
• For one or two tetrodes, including: 4CX250–350–400 (all types), 4CX800/
GU-74B, 4CX1000, 4CX1500B, 4CX1600A, 4CX1600U/GS-23B,
YL1050/52/56, GU-73B, GU-78B, GU-84B... and more.
• 'Universal' DC grounding – use with grounded cathode, grounded screen or
grounded control grid.
• Ideal for your new amplifier – or as an upgrade for your existing tetrode PA.
Tetrode Boards: AN-1
Issue 1.22, June 2011
 1998-2011 IFWtech Limited
WARNING
These notes are intended for users who have sufficient experience
to work safely with high-voltage circuits.
Use at your own risk! We cannot accept responsibility for any
damage or injury.
DANGER - AC mains voltage and high DC voltages!
The names of tag connections on the boards are shown underlined, as in “the G2-REG OUT tag”.
On the PC boards and the Interconnections diagram, some labels had to be shortened to save
space, e.g. G2-REG OUT is labeled G2REG on the board and the Interconnections diagram.
CAUTION
DO NOT use the Tetrode Boards with a screen supply derived from the anode high
voltage through a dropper resistor – it will cause serious component damage!
Always use a separate transformer winding for the screen supply.
REVISION NOTES
AN-1 Issue No
G2-CONTROL
board Issue No
REC-G1-ALC
board Issue No
3B
3B
1.0, April 1998
Intermediate changes 1.1–1.19
Changes (where significant)
See earlier versions
1.20, Nov 2004
3B
3D
Major revisions, to give more help on the wider variety of
tetrodes that are now in use.
1.21, May 2006
3B
3D
R106 changed to 470Ω.
Many changes to Farnell stock codes.
1.22, June 2011
3B
3D
Minor clarification of setup instructions.
More changes to Farnell stock codes.
Any trademarks mentioned in this manual that are not the property of IFWtech Ltd are acknowledged
to be the property of their respective owners.
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CONTENTS
1. Features......................................................................................................... 4
2. Introduction................................................................................................... 4
2.1 What You Get....................................................................................... 4
2.2 What You’ll Need.................................................................................. 5
2.3 Choosing Configuration Options .......................................................... 5
3. Tetrode Grounding Connections ................................................................ 6
3.1 Grid Driven, DC-grounded Cathode ..................................................... 6
3.2 Cathode Driven, DC-grounded Screen Grid......................................... 7
3.3 Cathode Driven, DC-grounded Control Grid ........................................ 7
3.4 Screen-grid Components ..................................................................... 8
4. Screen-grid Supply Configuration .............................................................. 9
4.1 Examples of Tubes............................................................................... 9
4.2 Off-board Component Calculations .................................................... 11
4.3 On-board Component Changes ......................................................... 15
4.4 Further Information............................................................................. 15
5. Control-grid and Relay Supply Configuration ......................................... 16
5.1 Control-grid Supply............................................................................. 16
5.2 Relay Supply....................................................................................... 16
6. Basic Inter-board Connections ................................................................. 17
7. Power and Control Options ....................................................................... 19
7.1 TX/RX Changeover Sequencing ........................................................ 19
7.2 Coax Relay Voltage............................................................................ 21
7.3 HV Supply Control .............................................................................. 21
7.4 G1 Switching ...................................................................................... 21
7.5 Automatic Level Control (ALC) ........................................................... 22
7.6 Additional Fault Monitoring ................................................................. 22
8. Building the Kit ........................................................................................... 23
8.1 Mounting the Boards .......................................................................... 23
8.2 Assembling the Boards ...................................................................... 23
9. Initial Power-up ........................................................................................... 26
9.1 Procedure ........................................................................................... 26
9.2 Problems? .......................................................................................... 27
9.3 Screen Supply Adjustments ............................................................... 29
9.4 Screen-current Trip ............................................................................ 30
9.5 Control-grid Protection and ALC......................................................... 31
9.6 Warm-up Timer .................................................................................. 32
10. Power-up Your Amplifier............................................................................ 33
10.1 Final Checks....................................................................................... 33
10.2 RF Testing.......................................................................................... 33
10.3 Final ALC Adjustment......................................................................... 33
10.4 False Alarms ...................................................................................... 34
10.5 That’s All !........................................................................................... 35
11. Updates and Product Support................................................................... 36
Schematics ................................................................................................. 37–42
Components List ....................................................................................... 43–48
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1. Features
•
‘Universal’ control unit for almost any amateur-size Tetrode Power Amplifier and its High
Voltage supply.
•
Carefully designed to help your tetrodes deliver a high-quality signal.
•
Suitable for either one or two tubes.
•
Two compact PC boards (both 5in x 4in – boards can be stacked).
•
Regulated and adjustable screen-grid supply.
•
Regulated and adjustable control-grid supply.
•
Sequenced relay switching with transceiver RF drive inhibit.
•
Screen-grid currents monitored for sensitive fault detection. No risky grid fuses!
•
Fault conditions disable PTT and HV supply for safety – simply press RESET to recover.
•
Comprehensive metering.
•
User-configurable for special requirements, with help from these detailed Instructions.
For a general introduction to these circuits and the ideas behind them, see Power and
Protection for Modern Tetrodes by Ian White, G3SEK, in QEX for October 1997
(PDF version downloadable from the Tetrode Boards website – see Section 11).
2. Introduction
The full Tetrode Boards kit includes all the components for the PC boards, and some of the
hard-to-find accessories.
To give you the best possible value for money, we do not supply expensive ‘off-board’
components such as meters and large heatsinks. You can probably find these components much
more cheaply as surplus, or out of the junk-box.
2.1 What You Get
The full Tetrode Boards kit includes:
1. Two PC boards, tinned, ready-drilled, and with printed component locations
2. All the on-board components – premium quality for reliability
3. Power MOSFET (Q2) and mounting washers
4. Push-on tags for the on-board connectors
5. Two extra VDRs for mounting directly at the tube sockets
6. Complete schematics and these Instructions.
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2.2 What You’ll Need
This is a summary of the additional components that you’ll need. Most of these are easier to buy
surplus than at new prices, so we didn’t include them in the kit.
1. Mains transformer(s) to supply screen grid, control grid, relays and heaters. For the
4CX250/350/400 family, the transformer ratings should typically be:
• Screen grid: minimum AC voltage depends on requirements for regulated screen
voltage and current. Typical ratings are at least 0–330V AC, at least 100mA, but may
need to be higher for large tubes – check Section 4.2.3 before ordering a transformer.
CAUTION
If the AC voltage of the screen supply transformer is too low,
the voltage regulator will not be able to function correctly.
• Control grid: 0–105V AC (anywhere in the range from 100 to 150V AC) at 50–100mA.
• Relays etc: 15–0–15V AC 1A min for 12V coax relays, higher voltage for 24V relays.
Note: a center-tapped winding is essential here.
• Heaters: the appropriate AC voltage and current for the tube(s). Allow for voltage
drops in the heater wiring, and adjust for exactly the correct on-load voltage at the
tube pins.
2. RESET switch: SPST momentary push-button (low-voltage).
3. ALARM LED: ordinary 20mA red LED.
4. Heatsink for Q2: see notes on page 48.
5. Mounting pillars and hardware for the two PC boards.
6. M1: typically 0–50mA or 0–100mA moving-coil meter for screen grid current. The G2CONTROL board has provision for an optional meter shunt resistor R17.
7. M2: 0–10mA moving-coil meter for control grid current. The REC-G1-ALC board has
provision for an optional meter shunt resistor R108.
8. RF choke wound on a 100Ω resistor, for mounting near the tube (see Section 3.4).
9. Screen-cathode bleeder resistor Rs (see Section 3.4 for values and ratings).
10. Power resistors R12 and R14 (see Sections 4.2.4 and 4.2.5 for values and ratings).
You will also need some temporary resistors for the setting-up procedures.
2.3 Choosing Configuration Options
Every power amplifier is different, so there are many possible options for voltages, metering,
TX/RX control etc.
CAUTION
Please read ALL of Sections 3, 4, 5, 6 and 7 BEFORE you switch on the soldering iron!
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3. Tetrode Grounding Connections
CAUTION
Do not start to build the kit until you have read all of Sections 3, 4, 5, 6 and 7,
and have decided on the options you need to install.
You can use the Tetrode Boards with any configuration of DC and RF grounding of the tube(s).
Remember that RF grounding and DC (chassis) grounding are different! For example, the
screen grid of a tetrode is always RF-grounded, but in most configurations the screen is not DCgrounded to the chassis.
This section explains the three practical combinations of DC and RF grounding, and shows you
exactly how to connect the Tetrode Boards. Note that some configurations require additional
components, shown in the schematics below as Rs, Cs, RFC, Rd, VDR – see Section 3.4 for
more details of these components.
Two-tube Amplifiers
The Tetrode Boards can handle either one or two tubes, though only one tetrode (V1) is shown
in these examples. If yours is a two-tube amplifier, use the connection points marked →V2 on
the schematics below.
Also see the note on page 10 about Matched Pairs of Tubes.
3.1 Grid Driven, DC-grounded Cathode
G1
ToV2
V2
IF
V2 ISRFC,
USED,
RFC1,
VDR1
Repeat
Rd,REPEAT
VDR and
Cs atR2,
each
tube
RFC1 RFC
SEE TEXT
V1
G1 BIAS
G2
INPUT CIRCUIT
Rd
R2 100Ω
100R1W
1W
RF
Rs
R1
Rs
SEE TEXT
CATHODE
VDR
VDR1
Cs
C1
RF drive is to the control grid, and the screen grid is bypassed by Cs (usually built into the tube
socket). The tube cathode is grounded to chassis (maybe through a small RF feedback resistor
at X).
Connect both of the CATHODE tags on the G2-CONTROL board and on the REC-G1-ALC
board to chassis ground as shown above. Do not connect the G1 OUT and G2-REG OUT rails to
chassis!
Note that the G1 meter is at control-grid potential below chassis ground, and the G2 meter is at
VG2 potential above chassis ground. Your anode-current meter in the B-minus rail will be at
chassis ground potential.
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3.2 Cathode Driven, DC-grounded Screen Grid
G1
If V2 IF
is V2
used,
repeat Ca
at eachVDR1,
tube C1
IS USED,
REPEAT
V1
G2
V2
C1Ca
Rs
R1
SEE TEXT
VDR
VDR1
CATHODE
B-MINUS
V2
INPUT CIRCUIT
RF
C2Cb
10n
RF drive is to the cathode, the screen grid is DC-grounded (so there is no screen bypass
capacitor Cs). The control grid is bypassed to chassis ground by Ca. The RF bypass capacitor
for the input circuit is shown as Cb. Ca and Cb should both be 10-100nF; VHF/UHF amplifiers
may need additional capacitance here.
Connect the G2-REG OUT tag on the G2-CONTROL board to chassis ground as shown above.
Do not connect the CATHODE or G1 OUT rails to chassis!
Note that the G2 meter is close to chassis ground potential, but the G1 meter is at (VG2 + VG1)
potential below chassis ground. Also your anode-current meter in the B-minus rail will be at VG2
potential below chassis ground.
3.3 Cathode Driven, DC-grounded Control Grid
G1
To V2
V2
Repeat RFC, Rd, VDR and Cs at each tube
IF V2 IS USED, REPEAT RFC1, R2, VDR1, C1
RFC1 RFC
SEE TEXT
V1
G2
Cs
C1
R2 100
100R
1W
Rd
Ω 1W
Rs
R1
SEE TEXT
V2
VDR
VDR1
CATHODE
B-MINUS
INPUT CIRCUIT
RF
Cb
C2
10n
RF drive is to the cathode, the control grid is DC-grounded and the screen grid is bypassed by Cs
(usually built into the tube socket). The RF bypass capacitor for the input circuit is shown as Cb,
and should both be 10-100nF; VHF/UHF amplifiers may need additional capacitance here.
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Connect the G1 OUT tag on the REC-G1-ALC board to chassis ground as shown above. Do not
connect the CATHODE or G2-REG OUT rails to chassis!
Note that the G1 meter is close to chassis ground potential, but the G2 meter is at (VG2 – VG1)
potential above chassis ground. Also your anode-current meter in the B-minus rail will be at VG1
potential below chassis ground.
3.4 Screen-grid Components
This section describes the components that are common to all of the schematics above.
RFC1 RFC
SEE TEXT
V1
G2
Rd
Ω 1W
R2100
100R
1W
Rs
R1
SEE TEXT
CATHODE
VDR1
VDR
C1
Cs
Screen-cathode bleeder resistor Rs
Rs serves two purposes:
1. To prevent the screen grid from ‘floating’ when the screen switching relay K1 is changing
over.
2. To provide a bleed current which makes the screen current meter read up-scale by about
10mA. This allows negative screen currents of up to 10mA to be indicated in an ordinary lefthand-zero meter. A 0–50mA meter will read screen current from –10mA to +40mA.
To obtain a bleed current of about 10mA, R1 = VG2 / 10 kΩ, e.g. 35kΩ for a 350V screen supply,
40kΩ for 400V etc. The value doesn’t have to be exact because you can ‘zero’ the meter to any
major scale mark using the mechanical adjustment. Section 4.2.1 gives some recommended
values and component ratings.
VDR
This VDR is identical to the two VDRs on the G2-CONTROL board. It is the first line of defence
to protect the screen grid, the screen bypass capacitor and the power supply in the event of a
flashover. Connect the VDR directly from the screen tag on the tube socket to the nearest
cathode tag, with short leads to minimize inductance.
There are already two VDRs on the G2-CONTROL board, but an extra VDR will be needed right
here at the screen grid of the tube. Because a two-tube amplifier needs a separate VDR at each
tube, two extra VDRs are provided with the kit (making four in total). If you are only using a single
tube, connect both VDRs in parallel for extra protection.
Cs - RFC - Rd
Cs is the screen bypass capacitor, and is usually built into the tube socket.
RFC and Rd prevent spurious resonances between Cs and the LF bypass capacitor C9 on the
G2-CONTROL board, which could lead to the screen grid becoming ‘un-bypassed’ at HF. Rd is a
100Ω 1W carbon or metal-oxide resistor (not wire-wound) and RFC is about 40 turns of 24gauge enameled wire, scramble-wound over the body of Rd.
If you use two tubes, you need a separate Cs-RFC-Rd network at each tube.
If the screen grid is directly DC-grounded, as described in Section 3.2, then Cs, RFC and Rd are
not necessary.
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4. Screen-grid Supply Configuration
CAUTION
Do not start to build the kit until you have read all of Sections 3, 4, 5, 6 and 7,
and have decided on the options you need to install.
The Tetrode Boards can be used with many different tubes that have a wide range of screen
voltage and current requirements. For correct operation, you will need to select certain
component values, depending on the following factors:
• Type of tube
–
regulated voltage required
–
maximum positive screen current (without losing voltage regulation) per tube
–
maximum negative screen current (without losing voltage regulation) per tube
–
screen trip current, per tube
•
Number of tubes – simply multiply the current requirements by the number of tubes
•
Mains transformer
–
AC voltage
–
current capability and/or winding resistances.
4.1 Examples of Tubes
The following are examples of the wide range of tubes that have been used with the Tetrode
Boards, with some typical operating conditions and suggested settings for the screen current
trip.
Tube
Typical operating conditions
(SSB, Class AB1) *
Suggested
current trip level
(mA)
Screen voltage
(V)
Peak screen
current (mA)
GS-15B
350
1
8
4CX250B
350
5
15
4CX250R / 8930
375–400
5
15
4CX350A
375–400
–3
15
4CX400A
375–400
≤ 20
≥ 20
4CX800 / GU-74B
350
30
40
4CX1000A
325
≤ 35
≥ 35
4CX1500B
225
–15
20
4CX1600A /
GU-91B
350
240
48
21
55
30
continued...
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Tube
Typical operating conditions
(SSB, Class AB1) *
Suggested
current trip level
(mA)
Screen voltage
(V)
Peak screen
current (mA)
520
≤ 23
≥ 23
360–380
40
60
500
26
35
4CX1600U /
GS-23B
GU-73B
GU-78B
GU-84B
YL1050/1052/1056
*
These values are taken where possible from manufacturers’ data sheets, or selected from information
developed by amateur users. Data given here are in no way warranted by IFWtech Ltd.
The screen current of a tetrode is a very sensitive indicator for a wide range of fault conditions,
including:
• Incorrect plate-circuit tuning
• Loading too light, or too heavy
• Too much RF drive
• Loss or major change in anode, screen or control grid voltage
• RF and DC arcs, flashovers and other ‘glitches’
• Blower failure, resulting in overheating of the tube(s).
All of these faults will result in too much screen current, either positive or negative. Continuous
electronic monitoring of the screen current is thus one of the most important features of the
Tetrode Boards.
The suggested current trip levels are normally about 20–25% above the ‘typical’ peak screen
current recommended by the manufacturer. This is generally high enough to avoid false alarms
during normal operation, but still low enough to give adequate protection to the screen grid.
However, for some tubes the manufacturer’s recommended ‘typical’ screen current (at the
recommended screen voltage) equates to the maximum allowable power dissipation. Where this
limit applies, the ‘typical’ screen current is given as a ‘≤’ value in the table above, and the
suggested trip current is given as a ‘≥’ value. The screen trip in the Tetrode Boards is very fastacting if anything goes wrong, so in practice it may be OK to set the screen trip current to 20%
above the manufacturer’s maximum recommended current.
Matched Pairs of Tubes
Two-tube amplifiers require tubes that are well matched in terms of DC and RF
characteristics. New tubes from the same manufacturer should start out well-matched,
but they must then experience the same operating history.
Tubes from different manufacturers (even new) may not be well-enough matched for use
in a two-tube amplifier. Unless you are very lucky, used tubes with different operating
histories will have very different characteristics and should not be paired together.
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4.2 Off-board Component Calculations
This section gives simple worksheets to calculate the voltages, currents and off-board
component values for the screen regulator. Here is a very simplified schematic:
Standing current
Screen current
R14
+
–
K1
+
METER
R12
Unregulated
input voltage
Q2
R12/Q2
current
Bleed
currentRS
Rs
Regulated
screen voltage
VDR
+30V
Each of the worksheets below contains an example column based on 2 x 4CX800/GU74B tubes,
and a blank column where you can enter the values for your particular amplifier. (If your
calculated values are dramatically different from the example values at any stage, you need to
1
check your arithmetic!)
4.2.1 Screen bleeder resistor, Rs
Rs is the resistor connected between the screen supply and cathode potential, close to the
tube(s). The purpose of Rs is to ensure there is always a DC return path for the screen, even
while the relay contacts of K1 are changing over.
Rs is calculated to bleed about 10mA of current, but this value is not critical (and need not be
changed if using two tubes). Suggested values are:
Screen voltage range
Rs
Up to 250V
22kΩ 5W
250–400V
33kΩ 7W or 10W, or 2 x 15kΩ 5W in series
400–550V
2 x 22kΩ 5W in series
> 550V
Above the voltage limit of the Tetrode Boards
If in doubt, use the next recommended lower value of resistance here.
1
There is also an Excel spreadsheet on the Tetrode Boards website. The spreadsheet approaches the
problem in a different way, but the results are equivalent.
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4.2.2 Calculate the Trip Current and the Standing Current
The ‘standing current’ is the current that flows through R14 all the time the amplifier is in the TX
condition (K1 energized as shown above).
Fill out this worksheet:
Calculation steps
Your
amplifier
Example:
2 x 4CX800/GU-74B
A
Suggested current trip level, mA
(from table above, based on 20–25% above
manufacturer’s recommended peak screen
current)
40mA
B
Multiply A by 1.1
C
Multiply B by number of tubes
44 x 2 = 88mA
D
Round C upward to the next multiple of 10mA
88 rounds up to
90mA
40 x 1.1 = 44mA
This is the trip current
E
90 + 20 = 110mA
Add 20mA to D
This is the standing current through R14
4.2.3 Calculate the transformer AC voltage requirement
Fill out this worksheet:
Calculation steps
Your
amplifier
A
Recommended regulated screen voltage
(from table above, or tube manufacturer’s data)
B
Add 50V to A
C
Required standing current through R14
(= E from Section 4.2.1 worksheet above)
D
Multiply C by 0.75, and add to A
E
Choose whichever is larger, B or D
F
Round E upwards to the next multiple of 10
350V
350 + 50 = 400V
110mA
(110 x 0.75) + 350 =
432.5V
D is the larger =
432.5V
This is the minimum unregulated input
voltage that will meet your requirements
G
Example:
2 x 4XC800/GU-74B
432.5 rounds up to
440V
Continued...
440 / 1.2 =
367V AC
Divide F by 1.2
This is the minimum transformer voltage
(RMS AC) estimated to meet your
requirements
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CAUTION
The transformer voltage is an ESTIMATE based on typical transformers. The suitability of
any particular transformer cannot be guaranteed until the practical testing stage.
If in doubt, choose a transformer giving a higher RMS AC voltage than estimated here.
Notes on transformer AC voltage
Maybe the minimum AC voltage is higher than you expected? Remember that the unregulated
DC input contains 100/120Hz AC ripple, so the instantaneous minimum voltage can easily be 30–
50V lower than the average voltage that you measure with a multimeter. If the instantaneous
minimum voltage is too low, the voltage regulator will ‘drop out’ during the negative part of the
ripple cycles, and the ‘regulated DC’ screen voltage will have negative spikes at 100/120Hz. An
oscilloscope will show this very clearly.
In the worksheet above, the factor of 1.2 on line G is an allowance for the difference between the
average DC voltage and instantaneous value at the minimum of the 100/120Hz ripple cycle.
However, the actual minimum voltage will depend on the transformer winding resistances, so the
suitability of your particular transformer cannot be guaranteed in advance.
The only way to be certain is to check the screen voltage using an oscilloscope, and make sure it
is a clean, constant DC voltage with no negative 100/120Hz spikes. If you see small spikes, you
may be able to adjust R12 to remove them – see below.
4.2.4 Calculate R14
The purpose of R14 is to deliver the required standing current (= E from Section 4.2.1 worksheet
above) into the shunt regulator circuit. We do not know what the actual value of your unregulated
input voltage will be, so this calculation is only a first estimate. The exact value of R14 will be
adjusted on test (see later, in Section 9.3.1).
To calculate R14, fill out this worksheet:
Calculation steps
Your
amplifier
Example:
2 x 4XC800/GU-74B
A
Unregulated input voltage
(= F from Section 4.2.3 worksheet above)
440V
B
Recommended regulated screen voltage
(= A from Section 4.2.3 worksheet above)
350V
C
Voltage drop across R14 = A – B
D
Required standing current through R14
(= E from Section 4.2.1 worksheet above)
E
R14 = C x 1000 / D Ω
440 - 350 = 90V
110mA
90 x 1000 / 110 =
818Ω
This is the estimated value for R14
F
90 x 110 / 1000 =
9.9W
W R14 = C x D / 1000 W
This is the minimum power rating for R14 – use
a higher-rated component for better reliability
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Notes on R14
The recommended component for R14 is an Ohmite adjustable wirewound resistor. The
adjustment feature allows simple setup (Section 9.3.1) without having to swap resistors.
Ohmite part number D50K1K0 (1kΩ 50W max) will be suitable for R14 in almost all cases (see
Components List for ordering information). This resistor can be adjusted to any value below 1kΩ.
The power dissipation is up to 50W, proportional to the length that is actually being used. The
resistor is air-cooled, and with good ventilation it will run reliably at a moderate temperature.
4.2.5 Calculate R12
The purpose of R12 is to remove some of the heat load from the power MOSFET Q2.
To calculate R12, fill out this worksheet:
Calculation steps
Your
tube(s)
Example:
2 x 4XC800/GU-74B
A
Recommended regulated screen voltage
(= A from Section 4.2.3 worksheet above)
350V
B
Required standing current through R14
(= E from Section 4.2.2 worksheet above)
110mA
C
Maximum value of R12 =
(A - 80) x 1000 / (B + 20)
(350 - 80) x 1000 /
(110 + 20) =
2076Ω
This is the maximum value for R12 –
D
Round this resistance value down to the
nearest standard value
E
W R12 = (B + 20) x R12 / 10
2
2000Ω
2
6
(110 + 20) x 2000 /
6
10 =
33.8W
This is the minimum power rating for R12 – use
a higher-rated component for better reliability
Notes on R12
R12 can be either a large wirewound resistor mounted with good ventilation, or a 50/100W metalclad resistor mounted on a large and well-cooled heatsink. If you choose the second option, the
heatsink for R12 must be separate from the heatsink for Q2!
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4.3 On-board Component Changes
Very few on-board component changes are needed to configure the G2-CONTROL board for
different tubes.
4.3.1 Screen voltage
You should normally use the screen voltages suggested in the table on page 9.
The following table shows the on-board changes that may need to be made for screen voltages
from 210V up to the maximum limit of 550V. (‘OK’ means you should use the standard values in
the component list.)
Voltage range
VDR1, 2 *
LK3
R9
R10
210–260V
(4CX1500B, 225V)
V250LA40B
(marked 250L40B)
shorted
47kΩ
100kΩ 1W
metal film
275–350V
OK (V320LA40B)
shorted
33kΩ
OK (150kΩ)
320–420V
OK (V320LA40B)
shorted
OK (27kΩ)
OK (150kΩ)
410–560V
V420LA40B
(marked 420L40)
150kΩ 1W
(use the resistor
listed as R10)
OK (27kΩ)
220kΩ 2W
metal film
* Also use the same components for the two VDRs that are connected at the screen(s).
A total of four VDRs will be needed.
In recent issues of the Tetrode Boards kit, Q2 has been changed from an IRF840 (500V) to a
higher-voltage MOSFET, STP4NB100 (1000V). See the Components List for further details.
4.3.2 Screen current sensing
Resistor R15 sets the working range of the screen-current trip circuit. Choose a value for R15 so
that your trip current (D from the Section worksheet) falls about in the middle of its working
range. R15 should be a 1W power metal oxide resistor.
Trip current range
R15
10mA (GS-15B)
220Ω
30–60mA
82Ω
50–100mA
47Ω
70–140mA
33Ω
100–200mA
22Ω
4.3.3 Control-grid voltage
See Section 5.1.
4.4 Further Information
There is more detail about screen voltages and currents in Application Note 3, available from
the Tetrode Boards website:
• http://www.ifwtech.co.uk/g3sek/boards/tetrode/tetrode-3.htm – click Downloads.
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5. Control-grid and Relay Supply Configuration
CAUTION
Do not start to build the kit until you have read all of Sections 3, 4, 5, 6 and 7,
and have decided on the options you need to install.
5.1 Control-grid Supply
The control grid bias is generated from a negative supply that delivers approximately 10mA via
R105. The fixed shunt voltage regulator consists of zener diode D114 and transistor Q101, and
the grid bias potentiometer RV102 gives an adjustment range of about 5V (from the nominal
zener voltage to about 5V more negative).
For different grid bias voltage requirements, change the 33V zener diode D114 (1N5364B) to
another voltage in the 1N53xxB series. For example, 4CX250s with a screen voltage of +360V
typically require about –55 to –60V of grid bias, so change D114 to a 1N5370B (56V).
Depending on your transformer voltage, you may need to change R105 (and possibly also R103)
to deliver approximately 10mA DC into the bias regulator (approximately 5V measured across
RV102).
Also see Section 7.4 for information about optional control-grid bias switching.
5.2 Relay Supply
The bridge rectifier BR101 provides both positive and negative DC voltages, so you must use a
center-tapped winding (or two equal windings correctly phased). The input tags are labeled 18-018V AC; the center-tap connects to the center tag.
18–0–18V AC is a ‘universal’ input voltage that will usually work with both 12V and 24V relays.
For 12V relays only, 15–0–15V AC is recommended, though transformer voltages down to about
12–0–12V AC may work with some relays.
Do not use transformer voltages lower than 12–0–12V; such low AC input voltages will not give a
regulated +12V DC supply from U101. Do not use transformer voltages higher than 25–0–25V
AC; they will exceed the voltage ratings of C105 and U101.
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6. Basic Inter-board Connections
CAUTION
Do not start to build the kit until you have read all of Sections 3, 4, 5, 6 and 7,
and have decided on the options you need to install.
This section deals with the basic inter-board connections that all configurations will need.
The Interconnections diagram on page 37 shows all of these basic interconnections, and also
some of the Power and Control options (Section 7).
Basic Interconnections
1. Wire the REC-G1-ALC board and the G2-CONTROL board together as shown in the
Interconnections diagram (page 37).
2. Wire the CHASSIS GROUND points on the two boards to a secure chassis ground. Do not
rely on board mounting pillars for chassis ground connections.
3. Always wire the CATHODE tags on the two boards together. Also re-check Section 3 to
confirm you are using the correct DC-grounding options.
Now connect the following off-board parts:
4. Mains transformer
The tags on the REC-G1-ALC board are marked for typical input voltages. Connect the
transformer windings to the following tags on the REC-G1-ALC board:
–
Screen supply: AC voltage as calculated from Section 4.2.3
–
Control grid supply: typically 105V AC
–
Relay supply: typically 18-0-18V AC.
Do not use these transformer windings for any other purposes.
5. G2 current meter M1
The full-scale deflection of the meter should be a round number, above the maximum trip
current suggested in the table on page 9. Typically the meter movement will need to be either
0–50mA full-scale for small amplifiers, or 0–100mA full-scale for larger amplifiers.
Observe correct meter polarity as marked on the G2-CONTROL board. R17 is an optional
meter shunt for calibration.
A typical 0–50mA meter will indicate screen current from approximately –10mA to +40mA
(see Section 9.3.3 for a detailed explanation, and page 29 for a typical meter scale).
6. G1 current meter M2
For class-AB1 operation, this meter must normally be 0–10mA full-scale.
Observe correct meter polarity as marked on the REC-G1-ALC board. R108 is an optional
meter shunt for calibration.
7. RV102
This is the G1 bias control potentiometer, usually mounted on the rear panel.
8. ALARM LED and RESET switch
Mount these components on the front panel. Observe correct LED polarity.
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9. Q2
Mount Q2 on its own heatsink. There are a number of options, depending on the screen
voltage, the regulator standing current (Section 4.2.2) and the MOSFET you have selected for
(see further notes on page 48):
• An area of chassis that is cooled directly by cold air from the PA blower
• A finned heatsink of outside dimensions at least 4in x 3in x 1in, in a well-ventilated location
with the fins vertical
• A heatsink with direct fan cooling – even a small fan helps a lot.
Use the insulated mounting hardware provided. The special thermally conductive washer
requires no grease, but make sure there are no burrs on the heatsink – they can easily cut
through the washer. Connect the body of the heatsink to chassis ground for safety.
Take care to connect the MOSFET correctly to the GATE, DRAIN and SOURCE tags as
marked on the G2-CONTROL board, and do not expose the MOSFET to electrostatic
voltages.
CAUTION
If the total standing current (Section 4.2.2) is greater than about 100mA, you may
require two MOSFETs connected in parallel with equalizing resistors.
If this may apply to your amplifier, e-mail [email protected] for further details.
10. R12, R13, R14
R12 and R14 are large power resistors, and generate a lot of heat in the TX condition. If you
use metal-clad resistors, they must be mounted on a large heatsink using thermally
conductive grease (mounting on the chassis will usually not be good enough, and will cause
overheating). You can use a heatsink about the same size as the one for Q2 (4in x 3in x 1in)
–but do not make Q2 share the same heatsink!.
In the RX or Standby condition the power dissipation is much lower than on TX. No current
flows through R14, and only a small ‘keep-alive’ current flows through R13 and R12.
If the RX/Standby voltage across R13 is more than about 150V (unusual), use two identical
10kΩ 3W resistors in series.
11. PTT
This is the ground-to-transmit connection from the transceiver. Check that your transceiver’s
PTT output is capable of switching 12V at 140mA to chassis ground.
You can connect a SPST switch in series with the PTT line to disable the amplifier on
Standby.
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7. Power and Control Options
The Tetrode Boards offer a wide range of user options. You will need to configure these options
while you are assembling and interconnecting the boards.
CAUTION
Do not start to build the kit until you have read all of Sections 3, 4, 5, 6 and 7,
and have decided on the options you need to install.
7.1 TX/RX Changeover Sequencing
7.1.1 General options
This section gives you an overview of the options for TX/RX changeover sequencing.
Sequencing Requirements
The two DPCO relays K2 and K3 give you several options for TX/RX changeover sequencing.
When you press and release the PTT, K2 operates quickly but K3 operates slowly. This
combination of fast and slow changeovers can generate all the necessary TX/RX sequencing by
inter-linking appropriate contacts.
RX → TX
Fast
Screen relay K1
•
Coaxial relays
•
Slow
TX → RX
Fast
Slow
•
•
RF drive
(optional TX inhibit)
•
•
Grid bias switching
(optional)
•
•
When the PTT line is grounded, the current is about 140mA. When the PTT line is un-grounded,
the open-circuit voltage is regulated at +12V.
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7.1.2 Coax relay control
You have two options:
• Energized on transmit – the usual way.
• Energized on receive – less commonly used, but has the advantage of ‘failing safe’
and protecting your preamplifier when the system is not in use.
To use one of these options, you must wire the connections to the two relays K2 and K3 as
shown below.
COAX RELAYS ENERGIZED ON TX
COAX RELAYS ENERGIZED ON RX
G2-CONTROL BOARD
(TRACK SIDE)
NC
NO
NC
1
1
4
4
RL IN
RL IN
NO
1N4001
1N4001
7.1.3 TX inhibit
A common problem with TX/RX sequencing is that the transceiver starts to generate RF drive
before the PA is ready for it. The Tetrode Boards include a TX Inhibit feature that holds the
transceiver’s EXT ALC INPUT line fully negative, preventing RF drive until the correct time in the
changeover sequence. You can use this feature if your transceiver has an external ALC INPUT
connection, and if the transceiver’s ALC recovery is fast enough to allow an acceptably quick
2
changeover.
The TX Inhibit feature can only be used if you are also using ALC – see Sections 7.5 and 9.5.
Also, you cannot use both TX Inhibit and the G1 switching feature (Section 7.4) because they use
the same changeover contacts on K2 and K3.
G2-CONTROL BOARD
(TRACK SIDE)
NC
NO
1
K2 - FAST
TO 'INH IN' TERMINAL ON
REC-G1-ALC BOARD
K3- SLOW
4
RL IN
2
The Yaesu FT-990 and FT-1000 series have an alternative way to inhibit the transmitter until the
amplifier is ready. The transmitter will only operate when pin 8 of the BAND DATA socket is grounded.
To use this feature, wire the ‘N.O’ contacts of K2 and K3 in series, and use them to switch pin 8 to
chassis ground.
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7.2 Coax Relay Voltage
The operating voltage for the external coaxial relays is connected to RL IN on the G2-CONTROL
board.
If your relays work quickly and reliably with 12V DC, link +12V OUT on the REC-G1-ALC board
directly to RL IN on the G2-CONTROL board. The maximum total current from the +12V HV
ENABLE and +12V OUT tags is 1.5A, limited by the 7812 voltage regulator IC which also
provides short-circuit protection.
For 24V coax relays, link RL-UNREG on the REC-G1-ALC board to RL IN on the G2-CONTROL
board. The unregulated voltage is 24–25V, which should be enough to operate relays up to 24V
DC.
For other relay operating voltages, you must organize your own power supply. CAUTION –
MAXIMUM VOLTAGE 50V AC/DC.
7.3 HV Supply Control
The +12V HV ENABLE tag on the G2-CONTROL board is the safety interlock to your HV (B+)
supply. This tag provides +12V DC to a mains power relay in the HV supply. The control voltage
is available after the warm-up timer has cycled. If the trip circuit operates for any reason, the HV
control voltage is removed in less than 5 milliseconds.
HV control is an important safety feature. We strongly recommend that you use it!
To use the +12V HV ENABLE feature you must install a 12V DC-operated relay to interrupt the
mains supply to the HV transformer. Make sure that the relay is capable of handling and breaking
the maximum overload current of the transformer – with a large safety margin.
The maximum total current available from the +12V HV ENABLE and +12V OUT tags is 1.5A.
The current is limited by the 7812 voltage regulator IC which also provides short-circuit
protection.
7.4 G1 Switching
The Tetrode Boards offer you the option to switch the control grid to a more negative voltage on
receive. However, for most tetrodes, switching the screen grid to cathode using K1 is enough to
ensure zero anode current in the RX condition.
If you know that you will not require G1 switching, make a wire link on the REC-G1-ALC board in
place of R107, and ignore the rest of this section.
If you do require G1 switching, R107 (4.7kΩ 2W) is supplied with the kit. Also connect the G1
SWITCH tag on the REC-G1-ALC board to K2 and K3 on the G2-CONTROL board as shown
below, and connect the switched line to the CATHODE tag.
G2-CONTROL BOARD
(TRACK SIDE)
NC
NO
G1
SWITCH
G1 SWITCH
CATHODE
RL IN
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If you are using G1 switching, you may also need to alter R107 from the value provided in the kit
(4.7kΩ 2W), but do not exceed the tube manufacturer’s maximum grid-cathode voltage in the RX
condition.
Note that you cannot use both G1 switching and the TX Inhibit feature (Section 7.1.3) because
they use the same changeover contacts on K2 and K3.
7.5 Automatic Level Control (ALC)
The Tetrode Boards provide an automatic level control (ALC) output to feed back to your
transceiver. ALC is recommended to prevent overdriving your linear amplifier.
ALC is derived by sensing the control-grid current. The ALC circuit on the Tetrode Boards is
normally configured for class-AB1 operation. That should mean zero grid current under all
conditions of drive! In reality, ALC control will begin at a few hundred micro-amps of control-grid
current.
To use ALC, simply connect the ALC OUT tag on the REC-G1-ALC board to the EXTERNAL
ALC input of your transceiver. The ALC OUT tag provides an industry-standard negative voltage,
adjustable to suit your transceiver.
Even if you choose not to use ALC, the Tetrode Boards will still be monitoring your control-grid
current to protect the tube. The circuit will disable the PA and light the ALARM LED if you run
more than a few milliamps of grid current – reduce the RF drive level and press the RESET
button to continue.
7.6 Additional Fault Monitoring
The AUX TRIP IN tag on the G2-CONTROL board can be used to prevent PA operation if this
tag is grounded. For example you could use a blower airflow switch (open-circuit when air is
flowing).
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8. Building the Kit
CAUTION
Do not start to build the kit until you have read all of Sections 3, 4, 5, 6 and 7,
and have decided on the options you need to install.
The standard Tetrode Boards kit contains extra resistors that you can select according to the
screen grid voltage and current required. Sections 4 and 5 explained how to select these
values for specific tubes. (At the end of assembly, you will therefore have a few resistors left
over.)
If you are providing your own components, use the component list at the rear of this manual
(check the Tetrode Boards website for any updates) and follow these instructions as
applicable.
8.1 Mounting the Boards
Use the bare boards as templates to mark the chassis fixing holes (hole centers 4.5in x 3.5in).
Fix the two boards to the chassis on 0.5-in (12mm) pillars. Take care with insulation around the
isolated mounting holes – high-voltage tracks pass nearby. The REC-G1-ALC board generates
significant heat, so it must be mounted above the chassis to allow the heat to rise freely.
If you intend to stack the two boards, the REC-G1-ALC board must be mounted on top to
dissipate heat. Use 1.5-in (35–40mm) pillars. To give access to RV1 and RV2 on the G2CONTROL board for setting-up, drill out the two holes on the REC-G1-ALC board marked ‘RV1’
and ‘RV2’.
CAUTION
Do not drill the holes in the REC-G1-ALC board any larger than 0.25 in (6mm) diameter.
To adjust RV1 and RV2, use a slim INSULATED trimming tool, to avoid shock hazards or
short-circuits between the two boards.
8.2 Assembling the Boards
1. Insert the connector tags into the boards first.
Lay the board on a flat sheet of expanded polystyrene, component-side up. To insert a
connector tag, hold it with long-nosed pliers and tap it gently into place with a very small
hammer. When all the tags have been inserted, solder them to the PC pads underneath the
board.
2. Wire the above-board links using insulated solid wire.
The G2-CONTROL board has two links (LK1 and LK2) above the board. For screen supply
voltages up to 400V, also wire the link LK3 in line with R8. For higher voltages, use a second
resistor in this position (see Section 4.2).
The REC-G1-ALC board has two wire links (LK1 and LK2).
3. If necessary, install suitable meter shunt resistors: R17 on the G2-CONTROL board; and
R108 on the REC-G1-ALC board.
4. Identify the components in the kit – see below.
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COMPONENT MARKINGS
Check the markings on each component BEFORE you solder it in place...
make that a DOUBLE-check!
Facts of modern life
♦ Components are getting smaller.
♦ Markings are often microscopic – and often don’t agree exactly with the full part number.
♦ There are now two different resistor color codes.
♦ The whole world is changing over to solders that contain no lead.
Sorry, that’s just the way things are... we hope the following notes will help.
Resistors
Some resistors are marked with the familiar three-band value code, e.g. 10kΩ is brown-blackorange... BUT...
Many resistors in the kit are marked with the newer four-band value code: 1st digit, 2nd digit,
3rd digit (always black), number of zeroes. In this coding, a 10kΩ resistor is brown-blackblack-RED – so take care! If in doubt, measure the resistors with a multimeter.
Trimpots
These have a two-digit marking: 1st digit is value, 2nd is number of zeroes:
500Ω
52
1kΩ
13
10kΩ
14
Ceramic capacitors
The 10nF capacitors are marked 103 (read the code as “1, 0 and 3 more zeroes”, i.e.
10,000pF). The 0.1µF (100nF) capacitors are marked 104. The 4.7nF (4700pF) capacitors are
marked 472 or 4n7.7
Diodes
Check the small glass diodes carefully using a magnifier. All the 1N4148 diodes will usually be
banded together. Some of the zener diodes have the voltage in the part number – the
BZX79C12 diodes are 12V zeners, and the BZX79C15 diodes are 15V.
Transistors and ICs
Install all the small transistors and the TO-220 devices according to the outlines printed on the
board.
Q2 is mounted separately on its own large heatsink, following the G-D-S connections printed
on the board. (Note – the rectangular outline printed on the board is for an optional 3-pole
connector.)
Take extra care to install all of the DIL sockets with the index notch at the correct end.
Lead-free parts
In future, all parts will be supplied with lead-free plating – the boards are now silver-plated!
For reliable soldering, we strongly recommend you continue to use regular tin/lead solder.
(In Europe, this is still legal for home constructors.)
Heatsinks
You must provide the large off-board heatsink for Q2, as stated in Section 2.2. You must also
provide nuts and screws to fix the TO-220 transistor tabs to all of the heatsinks. For Q2
there is a plastic bush to insulate the bolt from the transistor tab, and also a special insulating,
heat-conducting washer– do not use heatsink compound with this washer.
For the three small heatsinks on the boards, use heatsink compound with a nut and bolt. No
insulation is required.
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5. Assemble the components to the two boards. Observe polarity of diodes, IC sockets and ICs.
Use a fine-tip soldering iron – watch out for missed pads and solder bridges.
6. Wire the two high-voltage links LK4 and LK5 under K1 on the G2-CONTROL board (view
below is from under-side of board). Use Teflon insulated wire or sleeving.
7. For on-board TX/RX wiring options, follow the instructions in Section 7 and wire the necessary
links in the area beneath K2 and K3 on the G2-CONTROL board.
8. When you have finished all wiring, remove flux residues, solder balls etc. from the under-side
of both finished boards, using denatured alcohol or isopropyl alcohol and an old toothbrush.
Rinse well and allow to dry.
9. Check both boards very carefully for missed connections, dry joints or solder bridges. Use
a magnifier!
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9. Initial Power-up
CAUTION
Do not connect the Tetrode Boards to the amplifier yet.
Do not insert tubes into the amplifier until you reach
Section 10 – Power-up Your Amplifier.
If you find any problems, look in Section 9.2 for help.
9.1 Procedure
Follow these instructions carefully. Check-off each step as you go.
1. Remove any socketed ICs.
2. Disconnect the following tags at the REC-G1-ALC board: G2-UNREG, +12V OUT, CCW and
RL-UNREG (if used).
3. Apply mains power to the transformer and check that the following DC voltages appear on the
REC-G1-ALC board:
• G2-UNREG to CATHODE: +450V (approx, depends on transformer voltage)
• CCW to CATHODE: –150V (approx, depends on transformer voltage)
• RL-UNREG to chassis +25V (approx, depends on transformer voltage)
• +12V OUT to chassis: +12.0V
• Pin 4 of U102 (LM324) socket to chassis: +12.0V
• Pin 11 of U102 (LM324) socket to chassis: –12.0V (approx).
CAUTION
If there are any problems here, fix them before you go any further.
4. Switch off and disconnect from the mains.
5. Replace the +12V OUT connector and the RL-UNREG connector (if used). Connect the
coax relays to pin 4 near K2 and K3. Connect the LED and RESET switch (the PTT test
below will not work without the LED connected).
Apply power to the mains transformer. If you have configured the G2-CONTROL board to
have the coax relays energized on RX (Section 7.1.2) they should change over when you
apply power.
Ground the PTT line: all relays should change over, with a sequenced ‘ker-lick’ from K2 and
K3. Un-ground the PTT line: all relays should change back, again with a sequenced ‘ker-lick’
from K2 and K3.
Switch off and disconnect from the mains. Then replace all the other connectors on the RECG1-ALC board.
6. Remove the tube(s) and the HV connector from the PA, and connect the Tetrode Boards to
the PA.
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CAUTION
Before this step, you must have installed the screen-grid components in the PA, as
described in Section 3.4.
In particular, you MUST have installed the screen-cathode bleeder resistor Rs!
7. Adjust R14 to the value that you calculated in Section 4.2.4. Set all trimmer potentiometers
and RV102 to mid-range. Insert U2 (748) on the G2-CONTROL board (observe polarity). Do
not insert the opto-couplers U3 and U103 yet.
8. Apply mains power to the transformer(s) and check that the correct voltages appear at all
terminals of the tube socket(s) in the RX condition:
• Nominal heater voltage (check again later, with the tubes inserted)
• G2 at same potential as the tube cathode and the CATHODE tag (because in the RX
condition G2-REG OUT is connected to CATHODE by K1)
• Approximately correct negative G1 voltage in RX condition (depending on your choice
for G1 switching – see Section 7.4).
• The ALARM LED should light dimly, but not brightly.
9. Ground the PTT line to switch to the TX condition, and check the G2 voltage again:
• G2 voltage should now be present, and should be approximately the correct value
with respect to the tube cathode and the CATHODE tag.
• Check that RV1 can vary this voltage around the required value. In case of problems,
see Section 9.2.1.
• Move the positive test probe to the G2 METER + tag (or the meter itself). The voltage
should be exactly the same as at the G2 tag on the tube socket. Un-ground the PTT
line and check that the voltage does not change significantly in the RX condition. This
checks the ‘keep-alive’ function that reduces power consumption in the RX condition.
10. Ground the PTT line and check the G1 voltage in the TX condition:
• Check for approximately correct negative G1 voltage in the TX condition.
• Check that RV102 can vary this voltage over a range of about 5V.
11. Switch off and disconnect from the mains.
9.2 Problems?
The most likely source of all problems is wiring errors – either between boards or on the boards
themselves.
9.2.1 Screen supply troubleshooting
Problem
Zero voltage at
screen grid
Possible Causes and Solutions
• Not in TX mode, i.e. PTT not grounded. (In RX mode, zero screen
voltage is correct !)
• Unregulated supply not reaching G2-UNREG IN tag – check wiring
continuity.
• K1 not switching, or under-board links to K1 missing.
• Check wiring continuity from G2-UNREG IN through to G2 METER + ,
G2 METER – and K1, and on to G2-REG OUT .
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Problem
Output voltage high
(unregulated – RV1
has little or no
effect)
Possible Causes and Solutions
• Q2 installed ‘backwards’ with gate and source connections
interchanged – check polarity (Q2 often survives this error).
• No shunt path through R14, Q2 and Q1 to CATHODE rail – check
wiring continuity.
• Q2 gate failure – handle Q2 with care and observe anti-static
precautions!
• Current leakage in D6 is preventing the MOSFET Q2 from turning on.
(If D6 is a 4.7V zener, as supplied with earlier kits, change this
component to a 12V zener – see the Components List.)
• Voltage on cathode of D7 (band) should be +82V with respect to
CATHODE rail.
• Voltage on collector (tab) of Q1 should be +30V with respect to
CATHODE rail.
• If Q1 collector voltage is +30V, then the reference voltage at pin 2 of
U2 should be +23V with respect to CATHODE rail.
• When the circuit is regulating correctly, the voltages at pin 2 and pin 3
of U2 should both be almost exactly 23V.
Output voltage low
(unregulated – RV1
has little or no
effect)
• Output from U2 not reaching Q2 gate.
• If the voltage is correctly regulated for a few seconds but then drops
out of control, the standing current is probably too high for a single
MOSFET (e-mail for details of modification).
9.2.2 Control grid supply troubleshooting
All voltages in this section are measured with respect to the CATHODE tag on the REC-G1-ALC
board, and are negative.
Problem
Possible Causes and Solutions
Zero output voltage
• Unregulated supply not reaching RV102.
Output voltage high
(unregulated –
RV102 has little or
no effect)
• If you are not using G1 switching, check that R107 has been replaced
by a permanent wire link.
• No path through Q101 to G1 SWITCH and CATHODE rail – check
continuity.
• When G1 SWITCH is linked to CATHODE, voltage on collector (tab)
of Q101 should be 0; voltage on emitter of Q101 (= RV102 CW tag)
should be -33V.
• If you are using G1 switching (Section 5.4), and the PTT is not
grounded, a high negative G1 voltage on RX may be correct !
Output voltage low
(unregulated –
RV102 has little or
no effect)
Tetrode Boards: AN-1
Issue 1.22, June 2011
• Check Q101, D114 and associated components for short-circuits.
28
 1998-2011 IFWtech Limited
9.2.3 ALARM LED Lights at switch-on
This can happen occasionally, due to switching surges. False alarms are more likely in wiring
layouts that have long ground connections. Simply press the RESET button and continue as
normal.
If problems persist, see Section 10.4 for possible solutions.
9.2.4 TX/RX sequencing
To investigate problems with TX/RX sequencing, you can slow down the make/break operation
of K3 by connecting a higher-value capacitor in parallel with C25.
If you have successfully arrived here, everything is basically working.
You are ready for the next stage of adjustments, in preparation for power-up
and RF testing.
9.3 Screen Supply Adjustments
Now is the time to set the screen standing current, voltage and trip current to the design values
that you selected in Section 4.2.
9.3.1 Screen standing current
1. Switch off and disconnect from the mains.
2. Connect a well-insulated current meter in series with R14 and apply mains power to the
screen transformer. Ground the PTT input, and you can then adjust R14 for the correct
standing current as calculated in Section 4.2.2.
WARNING – ELECTRIC SHOCK HAZARD ON R14!
Before making any adjustment to R14, always switch off, disconnect from the mains
and short-circuit the screen supply.
CAUTION
To avoid damage to the exposed windings of R14 (if you are using the recommended
Ohmite resistor), ALWAYS slacken the screw clip until it rattles and will move freely.
NEVER attempt to slide the clip while the circuit is live!
9.3.2 Screen voltage
If the screen supply has passed all the tests described earlier in this section, you should be able
to adjust RV1 on the G2-CONTROL board to the exact G2-REG OUT voltage required
(measured with respect to CATHODE – remember to ground PTT).
9.3.3 Screen meter
The exact screen voltage will also affect the current passing through the screen-cathode bleeder
resistor Rs (Section 3.4) and this in turn will affect the reading on the screen current meter. The
bleed current through Rs will make the meter read approximately 10mA up-scale from zero.
Use the meter’s mechanical adjusting screw to place the needle exactly on the 10mA scale mark.
This indicates zero screen current (the extra 10mA is going through the bleeder resistor). In
effect, a typical 0–50mA meter is now reading screen current from –10mA to +40mA.
Optionally, you can re-scale the meter to look something like this (drawn using AutoSketch).
Tetrode Boards: AN-1
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 1998-2011 IFWtech Limited
9.4 Screen-current Trip
This section explains how to set the screen-current trip to the value specified from Section 4.1.
First, fill out this worksheet to calculate the resistance value RL that will be needed to load the
screen supply up to the trip current level:
Calculation steps
Your
tube(s)
Example:
2 x 4XC800/GU-74B
A
Required screen voltage
(A from Section 4.2.3 worksheet)
350V
B
Required current trip level for a single tube
(A from Section 4.2.2 worksheet)
40mA
C
Multiply B by number of tubes
D
RL = A x 1000 / C
350 x 1000 / 80 =
4375Ω
E
W RL = A x C / 1000
350 x 80 / 1000 =
28.0W
F
Select appropriate resistors to make up RL
40 x 2 = 80mA
3.3kΩ 25W in series
with 1.0kΩ 10W;
or Ohmite D50K5K*
* The value of RL only needs to be as accurate as you wish to set the trip current – a few percent is accurate enough.
Setup Instructions
1. Switch off and disconnect from the mains. Disconnect the Tetrode Boards from the
amplifier.
2. Turn RV2 on the G2-CONTROL board fully clockwise.
3. Insert the opto-coupler U3 (observe polarity).
4. Apply power, and ground PTT. The ALARM LED should light dimly as usual – it should not
light brightly.
When PTT is grounded, confirm that the screen current meter comes up to the new zero
mark (see above).
Switch off and disconnect from the mains.
5. Connect the load resistor RL between the G2-REG OUT tag and the CATHODE tag on the
G2-CONTROL board.
Apply power, and ground PTT. The screen current meter should now read the correct trip
current level.
Confirm that the regulated DC voltage does not change when this load is applied. If you have
a suitable oscilloscope, also check that this voltage remains clean and constant under
maximum load. If you see negative spikes at 100/120Hz, these are caused by AC ripple on
Tetrode Boards: AN-1
Issue 1.22, June 2011
30
 1998-2011 IFWtech Limited
the unregulated input. You may be able to adjust R12 slightly to remove the spikes; but if this
is not possible, the transformer AC voltage is too low – you will need to review Section 4.2.3.
6. With the load resistance applied, rotate RV2 very slowly counter-clockwise until the ALARM
LED lights brightly and the relays drop out. If you overshoot, release the PTT, turn RV2 back a
little and press the RESET button. The LED should go dim again (it is normal that the LED
does not go out completely).
7. Switch off and disconnect from the mains. Remove the temporary load resistor and restore all
connections to normal.
The screen current trip will now protect the amplifier during your further tests.
9.5 Control-grid Protection and ALC
Many modern tetrodes are intended for class-AB1 operation, which should involve no control-grid
current at any time. The control grids of such tubes often have a very small power dissipation and
require protection against excessive grid current.
The Tetrode Boards will protect the control grid of tube against excessive grid current. The
circuit will disable the PA and light the ALARM LED if you drive the tube into more than a few
milliamps of grid current. (If this happens, reduce the RF drive level, and press the RESET button
to continue operating.)
Although class-AB1 amplifiers should operate with zero grid current at all times, tube
manufacturers state that small amounts of grid current are acceptable for peak signal sensing
purposes. The Tetrode Boards provide an automatic level control (ALC) output that is derived by
sensing a few hundred microamps of peak control-grid current.
(Some ceramic tetrodes also display negative control-grid current at medium levels of RF drive.
This appears to be normal for those tubes. At higher levels of drive, the grid current will turn
around and come upward through zero.)
Setup Instructions
1. Insert the LM324 op-amp U102 and the opto-coupler U103 (observe polarity). Turn RV103
fully counter-clockwise.
2. Disconnect both of the 105V AC tags from the REC-G1-ALC board. Temporarily connect the
G1 OUT tag to chassis ground (see hookup diagram below).
3. Disconnect the wire going to RV102 slider from the RV102 SLIDER tag on the REC-G1-ALC
board.
4. If you are using the TX Inhibit feature (Section 7.1.3), disconnect the lead to the INH IN tag on
the REC-G1-ALC board.
5. Apply power. With no grid current flowing, the voltages at the ALC OUT tag and the G1 TRIP
OUT tag should both be zero.
6. Remove power. Temporarily connect the RV102 SLIDER tag via a 22kΩ 0.5W resistor to the
+12V OUT tag. (Do not disconnect the 12V feed from +12V OUT to the G2-CONTROL board
– it will be needed for step 9.)
Tetrode Boards: AN-1
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31
 1998-2011 IFWtech Limited
+12V OUT
G1 TRIP OUT
G1 OUT
G1 METER +
G1 METER -
REC-G1-ALC BOARD
RV102 SLIDER
105V AC
DISCONNECT
G2_CTRL BOARD
M2
RV102
G1 BIAS
TEMPORARY GROUND
+
G1 CURRENT
DISCONNECT
22K
7. Apply power. The grid current meter should read 0.5mA. This current also flows through the
grid opto-isolator U103 and activates the protection and ALC circuits.
8. Confirm that RV103 is fully counter-clockwise. Then confirm that, at some point within
RV101’s total range of travel, the voltage at the ALC OUT tag will change quickly between 0V
and almost –12V.
Trouble-shooting for step 8:
• Problem: the ALC OUT tag is permanently at –11 to –12V, and RV101 has no significant
effect. Solution: short-circuit R122 (under the board) and repeat step 8. You should now be
able to vary the voltage correctly.
• Problem: the ALC OUT tag is permanently close to 0V, and RV101 has no significant
effect. Solutions: first check that you have the correct opto-isolator in U103 (the MCT5211,
not the 4N36). If that is not the problem, change R122 to 1.0kΩ and repeat step 8. You
should now be able to vary the voltage correctly.
9. Switch off power, and turn RV101 fully clockwise. Replace the 22kΩ test resistor with 3.3kΩ.
Connect the G1 TRIP OUT tag to G1 TRIP IN on the G2-CONTROL board.
Apply power, and observe that the grid current meter now reads about 3mA. Turn RV101
slowly counter-clockwise until the ALARM LED lights. Turn RV101 a little clockwise, and
press the RESET button to cancel the current trip. Now turn RV101 very slowly counterclockwise again, to find the exact trip point – if in doubt, repeat this step until you are sure.
10. Switch off and disconnect from the mains. Remove all temporary hookups and return all
connections to normal.
The above adjustments will ensure that full ALC feedback will be developed at peak grid currents
of only a few hundred microamps, and the amplifier will trip at 3mA to protect the tube(s). See
Section 10.3 for final ALC setup instructions.
9.6 Warm-up Timer
1. If you are using an ‘instant-on’ tetrode with a directly heated filament, you do not need the
warm-up timer at all. You can skip this section, and you can also leave out C15, D11, R19,
R20 and U5 from the G2-CONTROL board.
2. Switch off and disconnect from the mains, and insert U5 (LM555CN) in the G2-CONTROL
board (observe polarity).
3. Switch on the power – the ALARM LED will light brightly, and you will find that the PTT has no
effect.
4. After about 3 minutes the ALARM LED will go from bright to dim (the LED will not go
completely dark – this is normal). Now +12V appears at the +12V HV ENABLE tag and you
can use the PTT.
Tetrode Boards: AN-1
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 1998-2011 IFWtech Limited
10. Power-up Your Amplifier
10.1 Final Checks
1. Switch off and disconnect from the mains. Insert the tube(s) in the amplifier.
Connect the heater and G1 supplies but DO NOT connect the HV or G2 supplies.
2. Switch on the power and check the heater voltage, right at the tube pins.
Hint: stretch transparent plastic film wrap over the bottom of the PA chassis, so that you can reach all the socket
terminals with a sharp-pointed voltmeter probe while still applying cooling air to the tube(s).
3. Check that approximately the correct G1 voltage is actually reaching the tube pins, in both RX
and TX conditions.
4. Switch off and disconnect from the mains. Disconnect the heater supply and connect the G2
supply. Apply power and check that the correct G2 voltage is actually reaching the tube pins in
the RX and TX conditions.
5. Switch off and disconnect from the mains. Connect the heater and HV supplies. Apply power
and wait for the warm-up period to complete. If you have used the +12V HV ENABLE option
(which is strongly recommended – see Section 7.3) the HV will not be enabled until the end
of the warm-up period.
6. When the warm-up period completes, the ALARM LED will go dim and HV will be applied.
The tube anode current should still be zero until you key the PTT.
7. Ground the PTT line but do not apply RF drive. Adjust the control grid bias using RV102 to
obtain the correct zero-signal anode current.
Congratulations –the Tetrode Boards are completely checked out and ready for use!
10.2 RF Testing
RF testing of power amplifiers is outside the scope of this manual... but whichever way you do it,
the Tetrode Boards will protect the tube(s).
You should disable ALC feedback until you have finished testing the amplifier and established
correct RF drive levels. To disable ALC, turn RV103 fully clockwise.
10.3 Final ALC Adjustment
ALC adjustment should be the very last step in commissioning the amplifier.
Section 9.5 configured the ALC circuit for class-AB1 operation. That should mean zero grid
current under all conditions of drive! In reality, full ALC control will be available at a few hundred
microamps of control-grid current. You may just see the G1 meter move, but nothing more.
ALC is intended to deal with transient modulation peaks only. If the ALC meter in your transceiver
is flickering all the time you are speaking, reduce the RF drive to the amplifier until the meter only
flickers on occasional speech peaks. With correct adjustment of tuning and loading, this should
ensure a clean signal.
There are two alternative ALC adjustment procedures, depending whether or not you are using
the TX Inhibit feature (Section 7.1.3).
Tetrode Boards: AN-1
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 1998-2011 IFWtech Limited
If you ARE using TX Inhibit
1. Disconnect the PTT line from the transceiver to the G2-CONTROL board. Ground the PTT
tag at the G2-CONTROL board, so that the amplifier comes up to the TX condition,
independently of the transceiver’s PTT.
2. Key the PTT on the transceiver and apply full SSB modulation. If RV103 on the REC-G1-ALC
board is turned fully clockwise, you should see full RF output from the amplifier.
3. Turn RV103 counter-clockwise until the RF output from the amplifier is reduced to a very low
level under all conditions of drive. Do not turn RV103 beyond this point.
This sets the correct ALC level for TX Inhibit operation, and hopefully should provide good
ALC control under normal modulation conditions too. However, not all transceivers are
suitable for both normal ALC operation and TX Inhibit.
If you are NOT using TX Inhibit
Adjust RV103 on the REC-G1-ALC board for smooth ALC operation with your transceiver.
The ALC meter on your transceiver should only flicker on occasional speech peaks. If it
moves all the time you are speaking, reduce the RF drive to the amplifier.
If you choose not to use ALC
The Tetrode Boards will still be monitoring your control-grid current to protect your tube(s).
If you drive the tube into more than a few milliamps of grid current, the trip circuit will disable
the PA and light the ALARM LED. Press the RESET button and reduce the RF drive level.
10.4 False Alarms
You should not experience ‘false alarms’ and trip-outs when you press the PTT. If you do, it may
be due to voltage spikes on the control lines, or a spike of full RF power when your transmitter is
first keyed... or there may be a genuine intermittent problem such as sparking in the tube(s).
Trouble-shooting
Apply the following tests in the sequence shown:
1. Remove the tubes and test again by repeatedly keying the PTT. Re-check the screen current
trip setting that was described in Section 9.4.
2. Test again with tubes that are known to be problem-free.
3. Try shorter and thicker wires for the CHASSIS_GROUND straps on the two boards. Route the
CHASSIS_GROUND connections from both boards to a single point on the chassis.
4. Remove the G1_TRIP_IN connection to the G2-CONTROL board. If the false trips no longer
happen, there may be a spike on this line caused by inadequate grounding. Alternatively,
your transceiver may be producing a spike of full RF output when the key is first pressed.
If you cannot improve the grounding any more (step 2) then change R126 to 10K and insert a
10K resistor on the G2-CONTROL board in place of LK2.
5. If steps 3 or 4 do not work – perhaps because the problem is in your transceiver – increase
C14 to 0.47–1.0µF. This has the disadvantage of increasing the reaction time of the trip
sensing (but the main delay is still in the HV control relay).
6. If you are using DC-grounded screen, with the cathode and B-minus line floating below
ground, you may see a screen-current trip on TX/RX switching. This is because the switching
makes the B-minus line change potential, and thus charges and discharges the RF bypass
capacitors at the cathode. These pulses of charge/discharge current are sensed as ‘screen
current’ and may cause a false trip. The solutions are to check that the bypass capacitors are
not larger than needed for RF performance, and to equalize the total capacitances from
anode to chassis and from cathode to chassis. It may also help to increase C14 to 0.47–
1.0µF.
Tetrode Boards: AN-1
Issue 1.22, June 2011
34
 1998-2011 IFWtech Limited
10.5 That’s All !
You should not need to make any of the above adjustments again, except perhaps to readjust
RV103 (ALC output level) if you change transceivers.
The Tetrode Boards will continue to provide protection and stable operating voltages for your
amplifier under all operating and fault conditions.
Normal operation
Normally, the trip circuit will never operate, and the ALARM LED will stay dim.
When the screen-current trip operates, the ALARM LED lights and the PA is placed in Standby
mode with the screen voltage removed. HV will also be removed if you have used the +12V HV
ENABLE option, which is strongly recommended – see Section 7.3.
When the trip has operated, the tube heaters are still powered, so you only have to press the
RESET button to return to normal operation. Before you press the PTT, wait a few moments for
the HV to come up.
If there is still a fault, the trip will operate again as soon as you press the PTT.
Tetrode Boards: AN-1
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35
 1998-2011 IFWtech Limited
11. Updates and Product Support
Updates and further Application Notes will be provided on the web:
• http://www.ifwtech.co.uk/g3sek/boards
For advice on details not covered by these notes, you can e-mail G3SEK direct:
• [email protected]
If you purchased the Tetrode Boards from Tom’s Tubes in the USA, please e-mail
[email protected] to be included on the list for any future e-mail updates.
Tetrode Boards: AN-1
Issue 1.22, June 2011
36
 1998-2011 IFWtech Limited
Interconnections
330V AC
SEE NOTES
INH IN
CHASSIS GROUND
ALC OUT
18-0-18V AC
G2-UNREG OUT
CATHODE
+12V OUT
G1 TRIP OUT
G1 OUT
G1 METER +
G1 METER -
RL-UNREG
RV101 SLIDER
RV101 CW
G1 SWITCH
RV101 CCW
105V AC
REC-G1-ALC BOARD
SEE NOTES
Labels for terminals on the
boards are shorter versions
of the ones you see here.
12V
COAX RELAY OPTIONS
24V
M2
RV102
G1 BIAS
+
G1 CURRENT
RESET
ALC
RL IN
PTT
1
2
3
4
J1
TX/RX OPTIONS
SEE NOTES
G1
G2-CONTROL BOARD
G2-REG OUT
G2
G2 METER +
TO TUBE(S)
GROUND CATHODE / G1 / G2, AS REQUIRED
SEE NOTES
G2-UNREG IN
M1
CATHODE
G2 METER -
+
R14
G2 CURRENT
TRANSCEIVER
PTT
CHASSIS
+12V IN
+12V HV ENABLE
SEE NOTES
G1 TRIP IN
TO HV SUPPLY
AUX TRIP IN
SEE NOTES
ALARM
GATE
TO Q2 - DRAIN
R14
R12
CATHODE
SOURCE
R12
Tetrode Boards: AN-1
Issue 1.22, June 2011
37
 1998-2011 IFWtech Limited
G2-CONTROL Schematic – Sheet 1
G2-UNREG IN
TETRODE BOARDS
G2-CONTROL BOARD: SCREEN REGULATOR
R14 - SEE TEXT
R16 1k5
2
Issue 3C 040416 (c) IFWtech Ltd
1k
50W
typ
D8 1N5337B
U3A
4N36
(4.7V 5W)
(U3B on sheet 2)
1
R15 82R 1W typ
R13
10K 2W typ
1
K1A
BR1
RX
4
R17
Meter Shunt
2
+ Ig2
3
METER, 50mA
R10
150k 1W typ
C10
10n 1kV
R12 - SEE TEXT
D9 D10
1N4001
50-100W typ
- Ig2
R11 82k
VDR1
V320LA40B
K1B
G2-REG OUT
D
D7
BZT03C82
(82V 3W)
Q2
STP5NB100 typ
G
VO
VI
3
ADJ
2
C2
10u 35V
D6
BZX79C12
(12V 0.5W)
G DS
1
C3
100n
BZX79C15
(15V 0.5W)
D2
D4
1N4148
R4
39k
U2
748
C4
100n
2
Q1
TIP122
R3
470R
D3
1N4148
RV1
10k
C6
33p
D5
1N4148
5
1
4
C1
10u
C5
4n7
+23V reference
CATHODE
(COMMON NEGATIVE)
R7 22k
3
6
R2
4k7
VDR2
V320LA40B
+30V rail
R5
2k7
D1
R1 270R
C9
100n
1kV
RX
S
8
U1
LM317L
LK3
R8
470k
1W
7
C11
470n
C8
4n7 1kV
C7
100n
R9
27k typ
R6 22k
WARNING
EUROPEAN COMPONENT CODES
4k7 = 4.7k = 4700 ohms etc
4n7 = 4.7nF = 4700 pF etc.
Tetrode Boards: AN-1
Issue 1.22, June 2011
Q1 REQUIRES A SMALL HEATSINK
Q2 REQUIRES A LARGE HEATSINK
R12 AND R14 HAVE HIGH HEAT DISSIPATION
Values marked "Typ" depend on
screen voltage and current required see text and Components List
38
THE SCREEN VOLTAGE INPUT AND OUTPUT
ARE UNGROUNDED!
USER MUST PROVIDE GROUNDING
AS REQUIRED.
 1998-2011 IFWtech Limited
G2-CONTROL Schematic – Sheet 2
TETRODE BOARDS
G2-CONTROL BOARD: CONTROL CIRCUIT
USER-CONFIGURABLE RELAY SEQUENCING
Issue 3C 020317 (C) G3SEK
SEE APPLICATION NOTES
FOR WIRING OPTIONS
RESET
SW1
K2A
+12V REG IN
J1
"FAST"
K2B
78L05
1
2
3
4
U4
TO COAX RELAYS ETC
ALARM
LED
3
VI
1
2
GND
VO
5
U3B
4N36
R24
10k
C13
100n
R21
470R 1W
C16
100n
R26
10k
K3A
"SLOW"
K3B
Q4
2N4403
C12
10u
Q6
IRF9520
RL-IN : SUPPLY VOLTAGE INPUT
FOR EXTERNAL COAX RELAYS
4
R20
100k
D11
1N4148
R18
220R
U5
8
7
Q3
2N5061
C15
100u
6
5
R29
10k
RV2
R27
10k
LM555CN
VCC
GND
DSC
TR
THR
OUT
CNT
RST
1
D12
1N4001
R22
10k
2
Q5
MPS2222A
3
4
R23
10k
R28
82R 1W
R25
10k
D13
1N4001
2
R19
1M
500R
+12V HV ENABLE
(TO HV PSU)
K3 6V
C17
2200uF 16V
1
C14
100n
LK2
K1 12V
2
2
G1 TRIP IN
K2 12V
LK1
D15
1N4001
1
1
AUX TRIP IN
D14
1N4001
EUROPEAN COMPONENT CODES
4k7 = 4.7k = 4700 ohms etc
4n7 = 4.7nF = 4700 pF etc.
Tetrode Boards: AN-1
Issue 1.22, June 2011
D16
1N4001
D17
1N4001
PTT (GROUND)
39
 1998-2011 IFWtech Limited
REC-G1-ALC Schematic
RL UNREG (+24V)
TETRODE BOARDS
REC-G1-ALC BOARD
D119
1N4001
+12V OUT
1
18-0-18V AC
IN
D101-108
1N4007
C105
4700u 35V
G2-UNREG
330V AC
R101
100K 2W
C101
100u 385V
R102
100K 2W
C102
100u 385V
C107
100u 35V
7812
OUT
LK2
3
+12V
U102
D120
1N4001
C106
100n
C108
100n 35V
D118
BZX79C12
4
U101
C109
100n
11
R109
4K7 2W
GND
BR101
2W04
2
Board Rev 3D 000831 (C) G3SEK
-12V
R110 470R 1W
R113
100K
CATHODE
C103
220u 200V
D110-113
R103
1K5 2W
D114
1N5364B (33V)
1N5370B (56V)
D122
1N4148
C114
33p
R115 10K
U102A
LM324
D123
1N4148
3
1
R116 10K
1N4007
ALC OUT
RV103
10K
C113
100n
LK1
R120
1M0
R119
2K7
10
8
2
C104
100n 100V
105V AC
R106
10K 470R
1W
+12V
R105
3k3 2W
2
D117
1N4001
R128
22K
R108
R118 470K
C115 100n
Meter Shunt
6
AA BB
5
KK C
C
4
E
E
+
G1 METER 0-10mA
_
RV102
(REAR PANEL)
500R 1W
EUROPEAN COMPONENT CODES
4k7 = 4.7k = 4700 ohms etc
4n7 = 4.7nF = 4700 pF etc.
R117
470K
R121
R122
470R
G1 OUT
D116
C119
33p
10K
R124
RV101
1K
D115
9
C116
1u0
U103
MCT5211
1
Tetrode Boards: AN-1
Issue 1.22, June 2011
100R
12
C112
33p
C111
100n
R112 10K
Q101
TIP122
R114
14
G1 SWITCH
R104
100K 2W
D121
1N4148
13
INH IN
R107
4K7 2W (or link)
U102C
LM324
R111 10K
10K
C117
33p
U102B
LM324
5
7
C110
100n
6
R123
22K
R125 470K
U102D
LM324
R126
100K
D124
1N4148
G1 CURRENT
TRIP (TO Q3)
R127
33K
C121
100n
C118
100n
C120
100n
1N4001
40
 1998-2011 IFWtech Limited
G2-CONTROL Board Layout
Actual size is 5in x 4in
Tetrode Boards: AN-1
Issue 1.22, June 2011
41
 1998-2011 IFWtech Limited
REC-G1-ALC Board Layout
Actual size is 5in x 4in
If you are
stacking the
two boards,
drill 0.25in
(6mm) max.
See
warning
note!
Tetrode Boards: AN-1
Issue 1.22, June 2011
42
 1998-2011 IFWtech Limited
The Tetrode Boards
Components List
SUPPLIERS
There are many sources for most of these components. The Farnell # columns shows order
codes from Farnell Electronics (http://www.farnellinone.co.uk). Farnell have associate
companies in many countries, including Farnell Chicago in the USA (1 800 718 1977– note
that US order codes may differ).
In the USA, Mouser Electronics (http://www.mouser.com) is probably the best single source;
Digi-Key (http://www.digi-key.com) is also a good source for most parts.
Resistors and capacitors may be subject to minimum order quantities. Small quantities can
often be bought more cheaply from other dealers, e.g. Maplin in the UK.
Note that you must also supply some off-board parts – see this list and also Section 2.2.
‘TYPICAL’ VALUES
Some component values depend on the output voltages and currents required.
These values are marked ‘typ’ in the list below and in the schematics –
see the cross-references for further details.
Boards: G2-CONTROL issue 3B, REC-G1-ALC issue 3D
Manual: Issue 1.22, June 2011
43
 1998-2011 IFWtech Limited
The Tetrode Boards
Components List
Capacitors
Total
C#
Value
Volts
Comments
Farnell #
5
C6, C112, C114,
C117, C119
33pF
100
Ceramic, 0.1" radial leads
941-1682
1
C5
4n7 (4700pF)
63
Ceramic, 0.1" radial leads
114-1780
1
C8
4n7 (4700pF)
1000
HV ceramic, Murata
952-7249
1
C10
10n (0.01uF)
1000
HV ceramic, Murata
952-7222
16
C3, C4, C7, C13,
100n (0.1uF)
C14, C16, C106,
C108, C109, C110,
C111, C113, C115,
C118, C120, C121
63/50
Multilayer ceramic, 0.2"
radial leads
121-6445
1
C104
100n (0.1uF)
100
Polyester, BC (formerly
Philips) 368
121-5469
1
C9
100n (0.1uF)
1000
Polyester, BC/Philips 375
1.1" radial leads
116-6096
1
C11
470n (0.47uF)
100
Polyester, BC/Philips 368
0.6" radial leads
121-5478
1
C116
1.0uF
50
Electrolytic, 0.1" radial
969-3734
3
C1, C2, C12
10uF
35
Electrolytic, 0.1" radial leads
945-1242
1
C15
100uF
16
Electrolytic, 0.1" radial leads
945-1080
1
C107
100uF
50
Electrolytic, 0.2" radial
945-1412
2
C101, C102
100uF
385
Electrolytic, Panasonic
TSUP
119-8738
1
C103
220uF
200
Electrolytic, Panasonic
TSUP
119-8575
1
C17
2200uF
16
Electrolytic, 0.2" radial leads
945-1137
1
C105
4700uF
35
Electrolytic, Panasonic
TSUP
119-8715
Boards: G2-CONTROL issue 3B, REC-G1-ALC issue 3D
Manual: Issue 1.22, June 2011
44
 1998-2011 IFWtech Limited
The Tetrode Boards
Components List
Resistors
‘R’ in resistor values means Ω, e.g. 15R = 15Ω, 0R33 = 0.33Ω, 3K3 = 3.3kΩ, 1M0 = 1.0MΩ etc.
1W, 2W and 3W resistors are metal film power types, e.g. BC/Philips PR02 and PR03.
Total
R#
Value
("R"= Ω)
W
Comments
Farnell #
135-7877
1
R15
47R typ
1
1
R28
82R
1
173-8572
1
R114
100R
0.25
934-1099
1
R18
220R
0.25
934-1528
1
R1
270R
0.25
934-1633
3
R3, R106,
R122
470R
0.25
934-1943
2
R21, R110
470R
1
156-5391
1
R12
1K typ
50
1
R14
1K
50
See Section 4.3.2 for
alternative values
Optimum value will
vary – see Section 4.2.5.
Calculate the correct
value before ordering.
1K0 50W metal-clad supplied
in kit, but may not be optimum
for all applications.
950-8163
Wire-wound adjustable resistor
– see Section 4.2.4.
Mouser: 588D50K1K0
Digi-Key:
D50K1K0-ND or
AVT50-1.0K-ND
1
R16
1K5
0.25
934-1323
1
R103
1K5
2
933-8110
2
R5, R119
2K7
0.25
934-1641
1
R105
3K3
2
933-8217
1
R2
4K7
0.25
934-1951
2
R107, R109
4K7
2
933-8268
13
R22, R23, R24, 10K
R25, R26, R27,
R29, R111,
R112, R115,
R116, R121,
R124
0.25
934-1110
1
R13
4
R6, R7, R123, 22K
R128
10K
3
If the RX/Standby voltage
across R13 is more than about
150V (unusual), use two
identical 10K 3W resistors in
series.
173-8702
934-1544
0.25
Boards: G2-CONTROL issue 3B, REC-G1-ALC issue 3D
Manual: Issue 1.22, June 2011
45
 1998-2011 IFWtech Limited
The Tetrode Boards
Components List
Total
R#
Value
("R"= Ω)
W
Comments
See Section 4.3.1 for
alternative values.
Farnell #
934-1650
1
R9
27K typ
0.25
1
R127
33K
0.25
934-1757
1
R4
39K
0.25
934-1862
1
R11
82K
0.25
934-2281
3
R20, R113,
R126
100K
0.25
934-1129
3
R101, R102,
R104
100K
2
933-8071
1
R10
150K typ
1
3
R117, R118,
R125
470K
0.25
934-1978
1
R8
470K
0.75
949-7749
2
R19, R120
1M0
0.25
934-1137
0
R17
Meter
shunt
Not provided in kit
0
R108
Meter
shunt
Not provided in kit
RV #
Value
Comments
1
RV102
500R
1W
Allen-Bradley W1 series,
rear panel mounted
121-9020
1
RV2
500R
Bourns 3306P series
108-235
1
RV101
1K
Bourns 3306P series
108-236
2
RV1, RV103
10K
Bourns 3306P series
108-239
See Section 4.3.1 for
alternative values
933-7768
Farnell #
Boards: G2-CONTROL issue 3B, REC-G1-ALC issue 3D
Manual: Issue 1.22, June 2011
46
 1998-2011 IFWtech Limited
The Tetrode Boards
Components List
Semiconductors etc
Total
Part #
Type
A / PIV / W
Comments
Farnell #
2
BR1, BR101
AM152 (2W02)
2A 200V
938-1449
2
D1, D2
BZX79C15
15V 0.4W
984-4511
8
D3, D4, D5, D11,
D121, D122, D123,
D124
1N4148
2
D6, D118
BZX79C12
12V 0.4W
109-7215
1
D7
BZT03C82
82V 3W
939-8490
1
D8
1N5337B
4.7V 5W
955-7946
13
D9, D10, D12, D13,
D14, D15, D16, D17,
D115, D116, D117,
D119, D120
1N4001
12
D101-108, D110-113
(D109 not used)
1N4007
2
D114 (kit contains two 1N5364B
alternatives)
1N5368B
965-5124
Or any highernumbered
1N400x
1A 1000V
33V 5W
47V 5W
956-4993
956-5051
See Section
4.3.3
955-8217
955-8250
2
K1, 2
8A 2PCO
12VDC relay, Schrack or Potter
& Brumfield type RTE24012
117-5020
1
K3
8A 2PCO
6V DC relay, Schrack or Potter
& Brumfield type RTE24006
117-5019
2
Q1, Q101
TIP122
100V NPN
980-4021
1
Q2
STP8NK100Z
Darlington
109-7115
Depends on screen voltage and current – see notes on page 48.
955-6524
1
Q3
2N5061
1V 350µA gate
1
Q4
2N4403
40V PNP,
hFE 100 min
E-B-C pinout
145-9019
1
Q5
MPS2222A
40V NPN,
hFE 100 min
E-B-C pinout
955-6842
1
Q6
IRF9530N
100V 6A,
Rds(ON) 0.6Ω
P-MOSFET,
G-D-S pinout
864-8603
1
U1
LM317LZ
Any LM317 in TO-92 package
948-8545
1
U2
UA748CN
Any 748 equivalent
(but must be a 748)
109-4418
1
U3
4N36
Current transfer ratio 100% @
10mA
102-1352
1
U103
MCT5211
Current transfer ratio 110% @
1mA
Digi-Key
1
U4
LM78L05ACZ
Any 78L05 in TO-92 package
948-9444
1
U5
LM555CN
Any CMOS 555
(but must be CMOS)
948-8243
1
U101
MC7812CT
Any 7812 (12V 1A, TO-220 pkg)
966-6109
1
U102
LM324N
Any LM324 in DIL package
975-5926
Boards: G2-CONTROL issue 3B, REC-G1-ALC issue 3D
Manual: Issue 1.22, June 2011
47
 1998-2011 IFWtech Limited
The Tetrode Boards
Components List
Total
4
Part #
Type
VDR1, 2
A / PIV / W
Comments
Farnell #
105-7150
V320LA40B typ See Section 4.3.1 for
alternatives
Install the 2 extra VDRs at the
tube sockets. For a 1-tube amp,
connect in parallel
Other parts
Total
Part #
Type
Comments
Farnell #
2
6 DIL socket
169-5668
2
8 DIL socket
118-2585
1
14 DIL socket
118-2586
1
For Q2
TO-220 mounting kit (‘dry’
silicone insulating washer
and plastic bush)
User provides
nut & bolt
522-636
3
TO-220 heatsinks
Vertical mounting with lugs
User provides
nuts and bolts
462-1281
60+
Connector blades
PCB mounting
2.8 x 0.8mm
25 for each
board
347-2528
60+
Blade sockets
2.8 x 0.8mm
25 for each
board
134-6446
Options for Q2
There are several options for Q2, depending on the screen voltage and current required.
• Voltages up to about 400V, screen currents up to about 100mA: IRF840 is best value.
• Higher voltages and/or higher currents: STP4NB100, STP5NB100 (TO-220 package);
or STW8NB100, IRFPF40, IRFPG30, IRFPG40 (TO247/TO3P package).
The kit is now supplied with the STP8NK100Z (Farnell 109-7115) which is good for most
applications.
When screen voltages and currents are high, the FET requires a specially good heatsink – an
area of chassis cooled directly by the PA blower is ideal, and even a small heatsink fan will help a
lot.
If the total standing current (Section 4.2.2) is greater than about 100mA, you may require two
MOSFETs connected in parallel with equalizing resistors as shown below. The transistors must
be mounted at least 40mm (1.5in) apart on the heatsink.
D
G
47
STP5N B100
x2
47
4.7 1W
NEMOS
4.7 1W
S
Boards: G2-CONTROL issue 3B, REC-G1-ALC issue 3D
Manual: Issue 1.22, June 2011
48
 1998-2011 IFWtech Limited
The Tetrode Boards
The Tetrode Boards
 1998-2011 IFWtech Limited