I'll start by saying that I'm a relative self-taught newbie in the electronics world. I recently bought a tube amp kit off of eBay. There were no assembly instructions included, but a very self-explanatory screen on the PCB made it easy to put together.

enter image description here

Power supplies are a gap in my knowledge; I usually just trust the product specs. But this fails my reasonability check, so I was hoping someone else could share their knowledge with me. According to the auction listing, "Power requirement is 60VAC ~ 70VAC 0.2A & 0 - 9VAC 1 ~ 2A."

First, I'd expect it to be an OR, not an AND for the two voltages. Second, when I try to google the power supply specs, I get overrun with results that match 60Hz...not VAC...and sifting through the results for something relevant is challenging at best.

If this isn't a type, I suspect that I may need to create SOMETHING that takes 120VAC in and uses two transformers to output 9VAC and 60VAC. If that's the case, I'd like some references to sites that have examples of "splitting" the power like that so I can research the circuit. I understand how to use a transformer to change 120VAC to X-VAC, but not sure if there are other considerations to get X-VAC and Y-VAC from a single 120VAC source.

If nothing else, it's a great time for me to start learning about power supplies. :)

  • \$\begingroup\$ Do you have a schematic of the circuit? \$\endgroup\$ – alexan_e Dec 22 '13 at 15:29
  • \$\begingroup\$ No schematics, unfortunately. I've emailed the company to request one; that'll make it easier I hope. The circuit is based on the Matisse Fantasy Line Stage...I may search for that and see what I come up with. \$\endgroup\$ – dwwilson66 Dec 22 '13 at 19:07
  • \$\begingroup\$ I see two TO220 devices near the capacitors, they seem to be related to the power supply, what are the codes? \$\endgroup\$ – alexan_e Dec 22 '13 at 19:10
  • \$\begingroup\$ Upper left corner is LT317, center between the two blue caps is C5171 \$\endgroup\$ – dwwilson66 Dec 22 '13 at 20:35

There are two solutions for this problem -

1)Use two transformers - one for 60VAC and other for 9VAC

2)Make a custom transformer having two secondary coils - one for 60VAC and other for 9VAC. This is a single transformer with 2 wires on primary side and 4 wires on secondary side(two for 60VAC and two for 9VAC)

There are solutions for splitting AC. But are costly. Best solution is to use transformers.

I have also faced a similar situation in building audio amplifiers where the power amplifier needs 22V and the filter circuit needs 12 volts and the solution was to build a custom transformer (since 22V was not a standard transformer rating).


This is a bit of a guess but I'd say you need two supplies like you suspected. One will be the main power source for the amplifiers and the lower voltage source will be for the filaments in the valves. I'd put a few pound sterling on a bet that both valve filaments are wired in series too because 9v is normally a little high for a single valve filament.

If it makes life easier use two transformers rather than trying to find one that has both secondaries.

  • \$\begingroup\$ I could see them running the tubes with DC filaments, and 9VAC rectified with a decent load probably gives you ~12V RMS DC. \$\endgroup\$ – Connor Wolf Dec 22 '13 at 19:34
  • \$\begingroup\$ @ConnorWolf that's how I thought too \$\endgroup\$ – Andy aka Dec 22 '13 at 20:30

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.