• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Bitsa Amp project

Avo111

Member
2015-09-28 7:26 pm
Please bare with an electronics numpty! I have been bitten by the valve electronics bug and am probably being over ambitious. So far I have built a Chinese SE EL34 kit that I got working with not a little help here. Along the way I discovered how tolerant valve electronics are to some quite stupid mistakes.

So I was going to learn more by messing about with amp 1 however it is so much better than I expected I want to leave it working as it is now plumbed into my Hi Fi. Plan B is to build another amp from bits I have found and have as left overs. The idea is as simple an amp as possible again using EL34 as the power valve in single ended operation. I have a power transformer with two 6.3V 1.5A windings and a 250V 340ma winding without a centre tap. I also have a couple of output transformers that were recovered from an old Blaupunkt radiogram. These are fairly small physically so I am not wanting to put too much through them. I also have a couple of EZ81 rectifiers. So I have cobbled up a schematic based on a couple of different ones I have found and would appreciate an intelligent and knowledgeable eye to be cast over the result for suggestions as to whether it is likely to work or whether I have done something really dumb!

I think I have created a triode strapped output with no feedback. Driver is half of a 6N1P, I also have Russian 6H9C that could work in this position, not sure which would be better. I am aiming for about 4W or 5W as that is what I am guessing the output transformers are good for. Any comments, criticisms or help much appreciated with this project.

Thanks
 

Attachments

  • Bitsa Valve Amp.pdf
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Avo111

Member
2015-09-28 7:26 pm
Ian,
Sadly I was given the Blaupunkt transformers already out of the original machine so I don't know what they were originally driven with. The Chinese EL34 amp is driving in pentode mode at 340V B+ which does look high according to the data, but seems to work OK. The screen is held at 225V by a 10K 2W resistor from B+.

Thanks