Download Layout and cabinet

DIY M-60 with 14 output tubes ( MA-I )
Layout and cabinet:
I’d like to stick, as much as possible, to the M-60 layout, because I thought that was the easiest way to avoid
hum and buzz problems. The cabinet it is made of MDF boards, and painted with metallic car-lack. All the tubes
are mounted on 6 mm solid copper plates, front and back panel, 8 mm copper plates. Output power supply
capacitors are mounted on 6 mm copper plates, then they are both mechanic and electric fastened. Size of the
cabinet 500x600x100 mm. Box to the transformers 450x170x170 mm.
Power supplies:
Driver stage power supply:
- Toroidal transformer: Designed to deliver 380-0-380V at 0.12A on each sec. winding. The transformer is rated
for 250VA. (or has a 250VA core, as we say)
- Tube rectifiers: Svetlana 6D22S
- Double choke input filter: 10H -100mF -10H - 100mF
- 10K bleeder resistors, mounted on the copper plates to the output supply capacitors.
Measured voltage at the driver stage 330Volt.
Output power supply:
- Two pcs. toroidal transformer: U=2x50V (1x100) The transformers are rated for 650VA.
- HEXFRED`s, IR HFA25TB60
- 12 pcs. of RIFA PEH 169 capacitors 4700mF 200V. A total of 56400mF.
Measured voltage on the capacitor rails 140 volts.
Output filament transformers:
- Two pcs. toroidal transformers. Designed to deliver 6.3V at 17.5A. The transformers are rated for 400VA.
Driver stage filament transformer, and driver stage rectifier filament transformer:
- toroidal transformer designed to deliver 2 x 6.3V at 1.25A on each sec. winding. And 2 x 6.3V at 4A on each
sec. winding. The transformer is rated for 250VA.
All transformers are custom made from ULVECO. Special features: Glued cores and transformer metal sheets
with random magnetic structure.
Driver stage:
- As mention above, tube rectifiers, and double choke input filter
- RCA 12SX7 tubes
- MIT MultiCap RTX 0.1mF coupling capacitors
Output stage:
- 14 output tubes
- metal film grid stop resistors
- metal oxide plate resistors
Others to mention:
- All 99.99% pure silver internal wiring
- Ceramic tube sockets
- Ten turns precision potentiometers
- No feedback circuit
- No meter
- No DC to driver tubes filament ( no hum or buzz at all)
- No 0.05 mF coupling capacitor from pin 7 of V1 and V2 to ground (still no hum or buzz)
- One push button at the back, to shut down one phase of the output power supply when adjusting bias.
- Something some people might not like, but to avoid the amplifiers look like a birds nest. I have mounted
HEXFRED`s, some coupling capacitors, and capacitors to the double choke input filter, on a PCB. There are
silver wire at the back.
- Total weight: 52Kg.
Start up:
The only thing that happened, was that I could not get enough bias. Then I reduced the value of the resistor in
series with the bias pot. to the half, and there it was.
Comments:
The power supplies are heavily dimensioned. The transformers are designed not to exceed 35 degrees Celsius.
That is why the VA rating is so high. I have also added quite a bit more, (higher VA) at the output power supply
transformers. The output supply filtering is also high 56400 microfarad. The RIFA PEH169 is some of the best
there is.
From my side there are some uncertainty:
1.Tubes rectifiers in the driver stage power supply, and double choke input filter. Frode, a friend of mine put me
on the idea, but I found the Svetlana 6D22S to be more suitable than the 6AX4GTB.
2. MIT MultiCap RTX coupling capacitors
3. Metal oxide plate resistors
Rune Brændaas