PX25 SE without NFB

[jamesjung21]

Hi
I had a good look through Google and I also tried searching through this forum but all I found are 3 schematics for PX25 SE.

Two of them are from Japanese DIYers and they both used negative feedback...

Does anybody know or have a PX25 SE circuit without NFB...?

Thanks
James

 

[SHiFTY]

Hey James

All you need is a driver circuit grunty enough- how about this:

Per channel- 1/2 12AU7->6SN7(both halves paralleled)->PX25

I have some data for this somewhere... It should be able to drive any triode, just adjust the plate voltage/cathode resistor/PX25 grid resistor and you would be away... I have great respect for the designer (schematic description in the first post of this thread)

Just remove the loop feddback and you are good to go...

 

[jamesjung21]

Hi SHiFTY,
Good to see you again

Actually I've just found this design with switchable NFB, which gives me both options...

http://www2u.biglobe.ne.jp/~tossie/PX25SE-E.html

I also have a U18 as used in that design, but I'll probably go with a GZ37 cause it has soft start...

BTW do you prefer the sound of EF37A to a Z729...?