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    Building, troubleshooting and testing of these amplifiers should only be
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GE 5670 at +/- 54v supply voltage

Hi all!
I have GE 5670 tubes, +/- 54v supply voltage and these scheme:


How to make it work together? :)
Be careful.
If you forget that the amplifier input 'ground' is -54 volts with respect to Earth, and connect another earthed unit to it (input or output) you will short out the lower half of the power supply.
Can you post the Power Supply schematic as rayma requested?
It might be possible to re-configure it as a voltage doubler - that gets you near 200 volts.
It might be possible to re-configure it as a voltage doubler - that gets you near 200 volts.

Not very likely as the voltage doubler ground will be at -54 to the amplifier center tap ground. This will work only with galvanically isolated grounds.

Certainly doable, but if one has to ask how to do it best thing is not to do it. High chances of sparks flying.

Edit: only now noticed this is an smps. Without messing with it the only safe and easy option is to build a valve circuit powered by the +54v rail.
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Need something like this:
but i don't know which cathode resistors should be and right my scheme or not. Help make corrections pls

You can use it basically as drawn with the following corrections:

1) decouple the -54V rail, at least copying what was done on the+54V one (2k resistor + 150uF cap; I´d use at least 1000 or 2200uF) because this is now the audio ground, as far as the tube is concerned.

2) add a series cap at the input, say 1Uf x 100V electrolytic, "-" side towards R1
Wonder why a mere 10k resistor was chosen for R1, would expect something like 220k instead.
Where did you pull this schematic from?

3) remember that audio signal will be applied to capacitor input and regular ground, do not use -54V as preamp ground.

4) output is already DC isolated by C3 BUT RV1 pot must be referenced to real ground also, not -54V

5) only to measure DC working point, you use -54V as tube ground and bias tube sections so plate voltage at idle sits roughly halfway between +54V and -54V

That this point is also near real ground is irrelevant.

6) to achive that, first power circuitb as-is, it might work properly; if not, vary cathode resistor values until you find the proper one.

7) you don´t want to add a power supply but you will still need to feed tube filaments.
How do you think you´ll achieve that?

8) what is the purpose of adding this anyway?


Paid Member
2011-10-31 1:00 am
I have a few. All they're really good for is testing, they need very good filtering to remove the hash. I do have one I may throw on a flea amp build.

Very good filtering? I had a noise coming from my preamp that I couldn't quite trace. It was even present without the tubes installed. I was using one of those adjustable ones for 250V for a pair of 6E2 meters. Guess where the noise was from? LOL Switched it for one of the fixed voltages ones I linked (making it the third of those in the same PS) and no more noise!

Even with a 4.5H choke and a 47u caps, there's still ~30kHz hash and garbage on the scope... The only thing I'd use the adjustable one for is my prototyping setup or a tube tester :p