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marinbnm 2nd November 2004 12:02 AM

Power Amplifier With EL 34
I got old power amp that is using a two EL 34 on output and one ECC 83 (i think ecc83 is used like preamp and phase turner, and as driver for output pair), it's got 25W output.
This amp i designed by Iskra Kranj, from ex. Yugoslavia, and is been used for cinemas around 1955- 1960'.
Power amp i mono, but i have two block.
Sound isn't good,because is old and maybe electrolic cap. are bad........, who knows(':(')
But i think building my own Audio Tube Power Amp, i want to use some parts from that amp, including power transformer, output transformer, tube holder, ..... (':smash:')
But i need a schematic for amp like that.
This is what i have:

-power transformer around 120W, and it's got about 2X 210V (AC POWER!), on secundar and of course voltage for filnament heating.

-Output transformer designed for EL 34 and 8ohm output speaker.

-EL 34, ECC 83 tubes.........

Resistors and capacitors aren't problem, but can somebody give me some good schematic based on stuff i got??
All this stuff i got double so isn't problem for stereo system to me!


:( :( :( :smash: :smash: :dodgy: :whazzat: :smash: ;)

SY 2nd November 2004 01:16 AM

One big determinant of a circuit to use is the output transformer. It is essential to know the primary impedance, whether there are UL taps and at what percentage, that sort of thing. There are other OPT specs that would be nice to know (primary inductance, leakage inductance, interwinding capacitance...), but let's start with turns ratio and taps.

yagoolar 3rd November 2004 08:34 AM


Here is a link to a howto "Determining output transformer impedance"
Determining output impedance ...

Anyway, I think it is better to look for the schematic of the PA you have and then replace old parts with NOS (caps at least). Using old parts to a new project is not a good idea, unless you know you can depend on those parts. If you are not sure, you may spend a lot of time on troubleshooting and the results might not be satisfactory.

If you still want to use them and build a new amp, there is a lot of those based on EL34 PP.

Is this a Hi(Fi) amp or for audio broadcasting system ? If it is the latter, then you probably need to replace output transformer. AFAIK such systems can drive 110 ohm line. Anyone correct me if I am wrong.

Best regards

marinbnm 3rd November 2004 01:31 PM

No i'm want use amp for audio systems.
I don't think that reparing old amp is not good idea, because i don't have schematic and amp is very old, but i don't want to use old electrolitic condenser anp resistor.....
From old amp i want to use only tube holder, power and outputtransformers, chasis.......
Hm... I'm know about determining output transformer impedance, but i think that this transformers are good because they allredy work as output for EL 34 amp, but i also will calculate that!
I got a pile of old schematic but can somebody give me a some schematic of amp like this, it's not have to be complicated.

Mark25 3rd November 2004 02:39 PM

I am doing a similar project myself. Rebuilding an AMC CVT3030 valve/hybrid amp, it too has EL34 PP o/p, but all the drivers are SS. I am only retaining the EL34's and O/P Tr's, a friend has given me these links as a start, maybe they are interesting for you too.

Power supply

Distortion specs

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