• 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.

Valve amp questions for someone new to them.

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I am not experienced in valve amps to say, all I can say is it sounds good so far and here are the pictures of the internals. Would like to learn more about this amp :)

Hope the pictures say more than I can
 

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Mark,

Kevin mentioned crosses to western types. I can provide a definite, a highly probable, and a potential, for the 3 tube types used.

I know the Chinese 5Z3P is equivalent to the U.S. 5U4G. The best current current production 5U4 is the ElectroHarmonix (EH) 5U4GB.

Comparing the data sheets for the Chinese 6J8P and the U.S. 6SJ7 reveals considerable similarity. Allow for the VERY conservative design center ratings on G.E.'s publication and few doubts remain.

My 1st reaction to a ST bottle power O/P type, with a top cap, was to think 807. The photo of the underside shows 5 pin sockets, which confirms the 807 idea. The 8 WPC produced is further evidence of 807 "finals".

Yes, the amp in question is single ended (SE), but it's 100% pentode. :yes: If an accurate schematic comes to light, I believe we will see Schade and/or global NFB. Pentode damping factor is quite poor, without help from NFB.
 
Please don't mention valve rolling, I have just spent 5 hours today reading about it all and am already sucked in.

Could someone please tell me what each valve does from left to right on my pictures? This is how new I am to it. I don't even know what each valve does :confused:

I am still enjoying the sound, and trying to find new and old music to listen to.

It does look like a sun audio 300b copy I don't know how the original sounds, but from what I hear, it sounds good to me
 
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I see the resemblance to the SUN amps, clearly borrows something from the layout approach.

Here is the Sun site: Sun Audio

High quality parts, very old school circuit designs. Well regarded here and in Japan. Not my cup of tea frankly. The kits are extremely expensive here.

On your Bowei the two tubes on the left are the driver tubes, the two with plate caps are the output tubes, and the fifth tube on the right is the rectifier.

For now just enjoy..
 
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URGENT: 807 IS NOT FD 422 Equivalent!

The FD 422 is a bona-fide direct heated pentode, [AKA DHP] you cannot replace this with an 807!

Looking at the PCB I noted that the filaments of the output tubes are heated with DC which made me suspect a DHP - when I looked it up that was indeed the case.

http://www.mif.pg.gda.pl/homepages/frank/sheets/095/f/FD422.pdf

This amplifier is a bit more exotic than I expected.. :D
 

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The fact that the output tube is a direct heated pentode makes it at least somewhat exotic.. :D Others may not agree.. :p

Anyway enjoy! I would get some more FD 422 as spares and more than likely there is a Russian cross to this type as well.

I'd recommend getting a complete set of spares against future need.
 
Thanks for the help guys, for now I will just enjoy the sound.

Then when I understand more then maybe look at rolling, or maybe using higher quality internals.

Am I right in thinking that all the sound is produced from the valves? So if I changed for higher quality internals it would have no effect?

I have always been used to SS amps, so this is new to me although I have a few Morgan Jones books on valve amp building. Always been interested.

A few questions you maybe able to help me with.

From what you have seen, do I have a good valve amp, eg, good design and in the future be able to upgrade this?

And the next, is how would a pentode differ to something like ECC34 mullards?
 
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