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Class A tube integrated circuit request

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Hi Everybody,

Can anyone provide the circuit for my reference about the 300B / EL34 integrated circuit with 20-30W per channel Class A design, PP/SE type are also acceptable.

Does anyone know how to calculate the power of the output transformer require for above cases ?

Any brand of Output in a modest price can be chosen ?

Thanks for your kindly help.
Sorry to make you confusing.

I want to construct one all tube integrated AMP about 20-30W Class A output.

1) Front stage and middle stage can use any type of tube.

2) Speaker driving part either EL34 or 300B tube can be used.

3) Output can use push-pull or single-ended design.

4) Not sure which kind of design and matching at point 1-3 will turn out better responds.


diyAudio Member
Joined 2004
More detail, please...

Does the integrated you want to build need a phono stage? If not, you should be able to use a volume control and source selector at the input of the amp, and there are plenty of P-P 300B and EL34 amp schematics out there.

You should be able to get 20 watts class A operation out of two 300B's, although you'd be pushing them pretty hard. It's doubtful you'll be able to get the same out of a pair of EL34's in triode mode, assuming that's how you want to use them.

Good luck.
Hello BHD,

Nice to see your reply.

Sure that I only want to make a simple integrated AMP without phono , no selector (single RCA connection), no tone etc.

You mentioned single 300B must be boosted to get a higher output, can i use SE parallel mode (two 300B/channel) solve the less output power ?

You are right said that "many circuits can found out there" . However, most of it didn't draw a whole picture associated with PSU and a short description. For example, the internal wiring connection and the majority part in ground plane.

In practical, I am not sure anyone have ever made these successful so that such circuit may not been verified.

I would like to make it by hand-wired and some part will use PCB (prefer in PSU) , if in case the circuit values and drawing have any mistake, I must get a great trouble.

Which brand of output transformer suit for me ?



diyAudio Member
Joined 2004
I'm not really a fan of paralleling tubes for single ended operation, but you could use 2-3 300B tubes (or more EL-34's) and get 20 watts (or more) power output.

Many of the amp schematics out there have a potentiometer at the input, allowing you to run a source straight in (usually a CD player). This isn't a bad way to go if you only have one source.


Parallel single ended EL-34:


Parallel single ended 6C33C (in German, use babelfish to translate):


Another parallel SE amp using One Electron transformers:


A parallel SE amp using three 2A3 output tubes from the same site:


The last couple aren't 20 watts, but you get the idea.

Do some google searches under "parallel single ended" "triode push pull" and the like. There are also a lot of schematics on this site. I'd also suggest checking out the links listed in the "online tube learning for newbies" sticky thread at the beginning of the tube section of the site.

Hope I've been helpful.

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