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Vacuum Tube Amplifier Design Program
Instructor: Chris Wen, Ph.D.
Program Objectives:
This course is focused on the design of vacuum tube preamplifiers and power amplifiers.
Electronic components such as resistors, capacitors, transformers will be discussed to
help students (or designers) select the most appropriate components. After this course,
students will be able to design and DIY their own vacuum tube amplifiers.
Total Hours: 12 hours
Schedule: 10:00-12:00, 12:30-14:30, June 9, June 16, June 23
(The schedule can be changed after the first meeting if all students agree)
Major topics:
1. Basic electronics
Ohm’s law, Kirchhoff's Voltage and Current laws, Thevenin’s Theorem
2.
(1)
(2)
(3)
Understanding electronic components
Resistors: type, characters, standard resistance, color band
Capacitors: type, specifications, selection
Transformer: power transformer, audio output transformer, transformer materials
3. Understanding vacuum tubes
(1) vacuum tube theory
(2) direct heated vacuum tube and indirect heated vacuum tube
(3) vacuum tube types
4. power supply design
(1) using solid state diodes
(2) using vacuum tubes
5. basic building blocks
(1)
(2)
(3)
(4)
(5)
common cathode triode amplifier
miller capacitance
decoupling capacitor
cathode follower
shunt regulated push-pull (SRPP) amplifier
6. distortion
7. preamplifier
8. Power amplifier design
(1) single ended amplifier
(2) push-pull amplifier
9. demonstration
(1) preamplifier
(2) single-ended amplifier
Vancouver Business and Technology
#6615, 8181 Cambie Road, Richmond, BC V6X 3X9
Tel: 604-2782176, 778-8898132
High Voltage, Danger!
1. Vacuum Tube = High Voltage
(12AX7: 300V-350V, 300B: 400V-450V, EL34: 450V, KT88: 450V-500V)
(211, 805, 845 >1000V)
2. It is the current that flow through your body kills.
3. Body resistance
The resistance of our skin varies from person to person and fluctuates between different times
of day. In general, dry skin isn't a very good conductor having a resistance of around 10,000
Ω, while skin dampened by tap water has a resistance of around 1,000 Ω.
4. Physiological effect
Using Ohm's law, we may derive the voltages lethal to the human body. This is given in the
following table:
Electric Current Voltage for Voltage for
Physiological Effect
Amperes
10,000 Ohms 1,000 Ohms
1 mA
10 V
1V
Threshold of feeling an electric shock
5 mA
50 V
5V
Maximum current which would be
harmless
10-20 mA
100 - 200 V
10-20 V
Sustained muscular contraction. "Cannot
let go" current.
50 mA
500 V
50 V
Ventricular interference, pain,
respiratory difficulty
100-300 A
1000- 3000 V 100-300 V
Basic Electronics
Ventricular fibrillation. Can be fatal.
1.
Ohm’s law
V=IxR
Voltage (Volt) = I (Ampere) x R (ohm)
I = V/R, R=V/I
2. Kirchhoff's Current Law (KCL)
This law is also called Kirchhoff's first law, Kirchhoff's point rule, Kirchhoff's junction rule,
and Kirchhoff's first rule.
The principle of conservation of electric charge implies that:
At any point in an electrical circuit where charge density is not changing in time, the
sum of currents flowing towards that point is equal to the sum of currents flowing
away from that point.
3. Kirchhoff's Voltage Law (KVL)
This law is also called Kirchhoff's second law, Kirchhoff's loop rule, and Kirchhoff's second
rule. It is a consequence of the principle of conservation of energy.
The principle of conservation of energy implies that:
The directed sum of the electrical potential differences around a circuit must be zero.
4. Thévenin's theorem
The Thevenin theorem states that any real source may be represented as an ideal potential
source in series with a resistor. In many cases, one may use the Thevenin circuit to solve
electronics problems that might otherwise be tedious at best. The ideal potential source
is called the Thevenin Voltage, VTH; The resistance is called the Thevenin Resistance,
RTH.
Thevenin Voltage is the voltage appears across the load terminals when you disconnect
the load resistor.
Thevenin Resistance is the resistance looking back into the load terminals when all
sources have been reduced to zero.
Example: Find the current flow across R5. R1 = 5 kΩ, R2 = 6 kΩ, R3 = 5 kΩ, R4 = 3 kΩ
Solution:
(1) Find VTH
(2) Find RTH
Example:
5. Capacitor circuit
(1) Parallel
(2) Series
(3) reactance
The current through the capacitor is proportion to the rate of voltage change
across the capacitor.
Since capacitors conduct current is proportional to the rate of voltage change,
they will pass more current for faster-changing voltages, and less current for
slower-changing voltages. What this means is that reactance in ohms for any
capacitor is inversely proportional to the frequency of the alternating current:
The unit of the reactance is ohm.
6. inductor circuit
The relationship between the voltage dropped across the inductor and
rate of current change through the inductor is as such:
Since inductors drop voltage is in proportion to the rate of current
change, they will drop more voltage for faster-changing currents, and
less voltage for slower-changing currents. What this means is that
reactance in ohms for any inductor is directly proportional to the
frequency of the alternating current. The exact formula for determining
reactance is as follows:
The unit of the inductive reactance is ohm.
Understanding Electronics Components
Resistors
Type of resistors:
1. Carbon Film Resistor
Low price, most popular, large temperature coefficient, tolerance 5%
Power: 1/8 W - 3W
2. Metal Oxide Film Resistor
Can withstand temperature up to 200℃, higher power, temperature coefficient is about
350PPM/℃, tolerance 2%, 5%
Power: 1/4 W – 5W
3. Metal Film Resistor
High precision, low noise, temperature coefficient is less than 100PPM/
℃, tolerance less than 1%.
Power: 1/8W - 3W
4. Carbon Composition Resistor
The resistive element is made from a mixture of finely ground (powdered) carbon and an
insulating material (usually ceramic). The mixture is held together by a resin. The
resistance is determined by the ratio of the fill material (the powdered
ceramic) and the carbon. Tolerances with 10% and 5% are the most
common.
The main advantage of Carbon Comps is their pulse handling
capability. This is due to the fact that the entire rod conducts.
Typically the 1W CCR1 can handle 35J. This is in contrast to 4J for a
wirewound resistor of similar dimensions.
(http://www.welwyn-tt.com/pdf/application_notes/CCR_AN_A.pdf)
(http://www.welwyn-tt.com/pdf/application_notes/CCR_AN_A.pdf)
5. Wire Wound Resistor
(1) Wirewound resistor
(2) Cement resistor
Cement resistors are made by winding resistance wires around non-alkaline
ceramic core, which is added with a layer of heat and humidity-resistant and
non-corrosive protective material.
Power: 2W-50W
(3) Aluminum Housed Wirewound Resistor
Power: 5W-120W
Resistor Color Code (or Color Band)
Standard Resistor Value
The Electronic Industries Association (EIA), and other authorities, specify
standard values for resistors, sometimes referred to as the "preferred value"
system.
E12
E24
E48
10% tolerance
5% tolerance (and usually 2% tolerance)
2% tolerance (also for inventory cost control in place of E96)
E96
1% tolerance
common ratio rN :
rN 
N
10
Where N is the E series number.
Standard EIA Decade Values Table (10-1000)
E12
10
12
15
18
22
27
33
39
47
56
68
82
E24
10
12
15
18
22
27
33
39
47
56
68
82
11
13
16
20
24
30
36
43
51
62
75
91
100
121
147
178
215
261
316
383
464
562
681
825
102
124
150
182
221
267
324
392
475
576
698
845
105
127
154
187
226
274
332
402
487
590
715
866
107
130
158
191
232
280
340
412
499
604
732
887
110
133
162
196
237
289
348
422
511
619
750
909
113
137
165
200
243
294
357
432
523
634
768
931
115
140
169
205
249
301
365
442
536
649
787
953
118
143
174
210
255
309
374
453
549
665
806
976
E96
Capacitor
A capacitor is an electrical device that can store energy in the electric field between a pair of
closely-spaced conductors (called 'plates'). When voltage is applied to the capacitor, electric
charges of equal magnitude, but opposite polarity, build up on each plate.
The capacitance of a parallel-plate capacitor is given by:
 A
C  0.2249 r 
 d 
Where
C = capacitance in picofarads
A= area of one plate, in square inches
 r = dielectric constant of the insulating material
0.2249= conversion constant
The dielectric constant εr or sometimes κ or K or Dk is defined as
where εs is the static permittivity of the material, and ε0 is vacuum permittivity.
Dielectric material
Dielectric const.
vacuum
1.00000
air(sea level)
1.00059
Aluminum Oxide
7.0-12.0
Ceramics
5.0-6.0
Mica
Polyester(PET, Mylar)
3.0-6.0
Polycarbonate (PC)
2.9-3.0
2.8-4.5
Polyethylene (PE)
2.25
Polypropylene (PP)
1.5-2.2
Polystyrene (PS)
2.4-2.6
Teflon (PTFE)
2.0
Capacitor Equivalent Circuit
ESL ( Equivalent Series Inductance): mostly results from wounding plates.
ESR (Equivalent Series Resistance): intermetallic resistance between leads and
plates, and resistance from plates.
Dielectric Absorption: Dielectric absorption is the inability of a capacitor to discharge
completely to zero. This is sometimes called battery action or capacitor memory and
occurs because the dielectric of the capacitor retains a charge.
There appears to be a strong correlation between the subjective sound quality of
capacitors and their dielectric absorption.
Polar plastics:
Some plastics are polar. At a molecular level within the dielectric, there are
permanently charged electric dipoles. Under the influence of an external electric
field, these dipoles attempt to align themselves to that electric field. When we
apply an AC field, energy is absorbed as we successively align these dipoles first one
way, and then the other, so that we incur a loss that rises with frequency. This is
sometimes known as electrostatic hysteresis.
material
Dielectric
polar
absorption
PTFE, Teflon
0.0002
N
PS
0.0002-0.0005
N
PP
0.0005
N
PC
0.001-0.01
Y
PET, Mylar
0.002-0.015
Y
Dissipation Factor (tangent of loss angle δ)
DF = (ESR/Xc) × 100% = ESR/(1/ωC) × 100%
Where ωis the frequency angular, ω=2πf.
Type of capacitor
Dissipation factor
Electrolytic Capacitor
0.1-0.4
Plastic film capacitor
0.001-0.01
Direct Current Leakage, DCL
DCL is the current leakage inside a capacitor. Usually it is listed as a specification for a
electrolytic capacitor. This is due to that the electrolytic capacitor uses very thin
aluminum oxide film as the dielectric material and uses high-purity aluminum foils which
are etched with billions of microscopic tunnels to increase the surface area in contact with the
electrolyte.
Direct Current Leakage is proportional to the working voltage and the capacitance of the
capacitor.
DCL  kCV
Where k is a constant, between 0.01~0.03. The smaller the better, but will be more
expansive. The capacitance is inμF and DCL is in μA.
Type of Capacitor
1. Film capacitor
(1) Plastic film capacitor
a. plastic film and foil capacitor
b. metallized plastic film capacitor
(2) Paper capacitor
2. Multi-Layer Capacitor
(1) Ceramic Capacitor
(2) Mica Capacitor
3. Electrolytic Capacitor
(1) Aluminum Electrolytic Capacitor
(2) Tantalum Electrolytic Capacitor
Plastic film capacitor:
a. plastic film and foil capacitor
b. metallized plastic film capacitor
plastic film and foil capacitor
This is the most important class of capacitors for use in valve amplifier,
as we will use these for coupling stages and also for precise filters.
Film/foil capacitors consist of two metal foil electrodes made of aluminum foil separated
by a piece of plastic film. The plastic film can be polyester, polypropylene or
polycarbonate. The thickness of the plastic film typically ranges from 2 μm to 20 μm,
while the aluminum foil thicknesses range from 5 μm to 9 μm.
A film/foil capacitor is made by alternating two pieces of aluminum foil with two layers
of plastic film. These interleaved layers are wound around a spindle in a manner that
prevents the metal layers from touching.
Metallized plastic film capacitor
Metallized film capacitors differ from film/foil capacitors in the sense that the aluminum
foils are replaced by a layer of metal vacuum deposited onto the film itself. The metal
layer is typically aluminum or zinc that is extremely thin in the range of .02 μm to .05
μm.
The advantage of these capacitors is their reduced physical size and their self healing
property.
Type of plastic film:
Polypropylene (PP)
Polyester (Mylar)
Polycarbonate (PC)
Polystyrene (PS)
Teflon (PTFE)
Polypropylene and polyester film capacitors are most common. Mylar capacitor is good
for general non-critical application. It is cheaper than other plastic film capacitors.
Teflon capacitor is very good, but it is big and expansive.
Self-Healing
The self-healing property is exclusive to capacitors with metallized films and is their
single biggest advantage over film/foil capacitors.
Self-healing is a phenomenon where in the event the electrodes are exposed to each other
instead of the capacitor shorting, the capacitor repairs itself. This repairing of the
capacitor is due to the thinness of the foils used.
In a film/foil capacitor when the foils are exposed to each other, the foils would touch
and short together rendering the capacitor useless.
Paper capacitor
A paper capacitor is made of flat thin strips of metal foil conductors that are separated by
waxed paper (the dielectric material). Paper capacitors usually range in value from about
300 picofarads to about 4 microfarads. The working voltage of a paper capacitor rarely
exceeds 600 volts. Paper capacitors are sealed with wax to prevent the harmful effects of
moisture and to prevent corrosion and leakage.
OIL CAPACITORS are often used in high-power electronic equipment. An oil-filled
capacitor is nothing more than a paper capacitor that is immersed in oil. Since oil
impregnated paper has a high dielectric constant, it can be used in the production of
capacitors having a high capacitance value.
Ceramic Capacitor
A Ceramic Capacitor is so named because it contains a ceramic dielectric.
MICA CAPACITOR
A Mica Capacitor is made of metal foil plates that are separated by sheets of mica (the
dielectric).
Aluminum Electrolytic Capacitor
An aluminum electrolytic capacitor consists of a wound capacitor element, impregnated with
liquid electrolyte, connected to terminals and sealed in a can. The element is comprised of an
anode foil, paper separators saturated with electrolyte and a cathode foil. The foils are high-purity
aluminum and are etched with billions of microscopic tunnels to increase the surface area in
contact with the electrolyte.
While it may appear that the capacitance is between the two foils, actually the capacitance is
between the anode foil and the electrolyte. The positive plate is the anode foil; the dielectric is the
insulating aluminum oxide on the anode foil; the true negative plate is the conductive, liquid
electrolyte, and the cathode foil merely connects to the electrolyte.
Tantalum Electrolytic Capacitor
What is Tantalum?
Tantalum is a chemical element in the periodic table that has the symbol Ta and atomic
number 73. A rare, hard, blue-gray, lustrous, transition metal, tantalum is highly
corrosion-resistant.
The cathode electrode is formed of sintered tantalum grains, with the dielectric
electrochemically formed as a thin layer of oxide. The thin layer of oxide and high
surface area of the porous sintered material gives this type a very high capacitance per
unit volume. The anode electrode is formed of a chemically deposited semi-conductive
layer of manganese dioxide, which is then connected to an external wire lead. A
development of this type replaces the manganese dioxide with a conductive plastic
polymer (polypyrrole) that reduces internal resistance and eliminates a self-ignition
failure
Compared to aluminum electrolytics, tantalum capacitors have very stable capacitance
and little DC leakage, and very low impedance at low frequencies. However, unlike
aluminum electrolytics, they are intolerant of voltage spikes and are destroyed (often
exploding violently) if connected backwards or exposed to spikes above their voltage
rating. Tantalum capacitors are also polarized because of their dissimilar electrodes.
Working voltage is limited up to 50 V.
Transformer Materials
Cold Rolled Grain Oriented Steel
Conventional CRGO (Cold Rolled Grain Oriented Steel) materials (M4, M5, M6)
are used regularly for cores in Transformers.
Cold Rolled Grain Oriented Steel
Magnetic
Flux
Material
Core Loss
New
Old
Thickness,
number
number
mm
30Z120
Z8
30Z130
Z9
30Z140
W/KG
Density
Density
Stacking
Kg/dm²
T
Factor %
W 17/50
W 17/60
B8
<1.20
<1.58
>1.80
<1.30
<1.72
>1.80
Z10
<1.40
<1.85
>1.80
35ZH115
Z7H
<1.15
<1.52
>1.88
35ZH125
Z8H
<1.25
<1.65
>1.88
35ZH135
Z9H
<1.35
<1.78
>1.88
0.30
0.35
7.65
7.65
>95.5
>96.0
35Z135
Z9
<1.35
<1.78
>1.80
35Z145
Z10
<1.45
<1.91
>1.80
35Z155
Z11
<1.55
<2.04
>1.80
Oriented Hi-B
Nippon Steel Corporation has come out with low loss Hi-B materials, which
guarantee low Watt Losses at 1.5 Tesla flux density. Such materials are called
Hi-B materials.
Cold Rolled Non Oriented Steel:
H6 – H20, Thickness 0.35mm or 0.50 mm, used for power transformer.
EI cores
Dimension of EI cores: mm
A
B
C
D
E
F
G
57
47.5
19
9.5
9.5
28.5
38
60
50
20
10
10
30
40
66
55
22
11
11
33
44
76.2
63.5
25.4
12.7
12.7
38.1
50.8
85.8
71.5
28.6
14.3
14.3
42.9
57.2
96
80
32
16
16
48
64
105
87.5
35
17.5
17.5
52.5
70
114
95
38
19
19
57
76
Relation between A, B,…..,G
C=2D
E=D
2D+2E+C=A , that is C+C+C=A
so
C=A/3
D=A/6
E=A/6
F=A/2
G=F+D=A/2+A/6=4A/6=2A/3
B=G+D=5A/6
Toroidal Core
The cores are wound by automatic core winding machine with a continuous
silicon steel strip and are annealed in high vacuum furnace under protection
atmosphere or in continuous tunnel furnace.
C-Cores
The cores are wound from grain oriented silicon steel strip and are annealed in
high vacuum furnace under protection atmosphere. The impregnation is done in
vacuum impregnating equipment, and low-stress and high-viscosity resin are
being used. Fine polishing process of cutting surface ensures very good
performance of the cores with low core loss and high saturation.
Vacuum tube theory
Edison Effect
Thermionic emission
Thermionic emission is the emission of electrons from the surface of a heated cathode or
filament.
Type of Cathodes: direct heated, indirect heated
Cathode materials
Tungsten: 2200-2500 C
Thoriated tungsten: 1900 C
oxide coated:
800 – 1150 C
The most common coatings are of strontium and barium oxides.