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Old 13th April 2003, 07:26 AM   #1
diyAudio Member
Join Date: Apr 2003
Location: Israel
Default Small pentodes push pull tube amps

Hello everyone

I am new to this forum though not new to DIY audio stuff, I have been building audio stuff for the last 25 years (mostly ss for the first 15 years and mostly tube stuff in the last 10).

I was very pleased to find this forum and seen some very interesting info. here.

Now to the point, I was playing around with some small power pentodes like 12eh5, 6an5, 50c5 etc. they can be found for next to nothing, run on relativly low voltage and when coupled to a good iron in PP configuration give fantastic sound both for headphone listening and close range listening.

However, In all my surches on the web I came across very few designes with these families of tubes (Steve bentch, Adam Von, and some jepanies designes).

Does anybody have any access to more designes with these tubes? I will post my schematics here shortly.

Thank you very much.

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Old 13th April 2003, 10:35 AM   #2
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Join Date: Feb 2003
Location: Birmingham, UK
A guitar amp using 35C5s can be found at:

It could be easily adapted for 50C5s or any other type of small output pentode.

I think that since the types of tubes you mention were really designed for AC/DC operation, now that many countries have electrical safety regulations which forbid using AC/DC technique in commercial equipment, there has not been any interest in producing new designs with these tubes.

One option would be to use the schematics of old tube sets with decent audio stages using these tubes, and update them using modern components.
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Old 13th April 2003, 10:52 AM   #3
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Join Date: Apr 2003
Location: Israel

First , thanks for the link. I think that one of these days I will build an amp of this kind.

You are right about AC\DC operation and safety regulations but the same tubes can be used for building safer topologies with isolation transformers and still be utiliesed for building good sounding amps.

Try building one I think you will love it.

I will appriciate any more info.


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Old 13th April 2003, 02:29 PM   #4
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Join Date: Feb 2003
Location: Birmingham, UK
I occasionally repair old tube radios, and have come across many AC/DC types, so I am aware of the capability of these tubes when used properly in decent audio stages, although often the stages are far from decent!

I once did make an AC/DC amp using 6Q7s in driver and phase splitter stages and PL38s in the output, with an enormous dropper resistor for the heater chain! No idea of the output, but it was loud! - mind you, that was about 25 years ago and I would not now use the AC/DC approach without an isolating transformer.

There are other circuits on the dogstar site, for example:

Good luck with your amp
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Old 13th April 2003, 03:03 PM   #5
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Location: Macedon NY
The 50C5 is the miniature version of the 50L6/25L6, and there are many circuits for those.

Several 25L6 Amps:

Westinghouse H-157 radio:

A Kodak projector amp:
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Old 13th April 2003, 11:13 PM   #6
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My 5-buck amp is an SE 50EH5.

I have a pr of SE chassis with much nicer 50eh5 OPTs and am noodling about doing a PP amp with twin SE OPTs (similar to what Steve Deckert is doing with his Torii).

community sites,, ........ commercial site planet10-HiFi
p10-hifi forum here at diyA
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Old 14th April 2003, 08:58 AM   #7
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Hello all and thanks for the good info.

Most of the sites I am bumping into on the net are in US, western Europe and very few in Japan. does anyone know how can I get info. from east Europe and\or the far east? they have many designs (Russian radios Japanies radios etc.) that I am sure will be very interesting to look at.

Thanks again.

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