Winter project: Pilot AA-920 conversion to power amp

[s-petersen]

I think I'm done with the FB adjustments, I may still try to do something about the start up surge in the HV.
Here is the current configuration. The cathode resistors are 300 Ohm, but they will be 360 because the Russian tubes get a little hot.
with 1K BASE The amp is down .9db at 20k if I figured it correctly 5v sine at 1k 4.5v at 20K
26 watts before clipping starts

10K


1K

 

[battradio]

Well are you happy the way it sounds ,

 

[s-petersen]

It's a little early(late) to make noise, Likely when I get up for work I'll give it a try,(2pm)

 

[s-petersen]

Sounds Awesome!

 

[DrRick1955]

Regarding the gain, you can increase it by adding a bypass cap across the cathode resistor on the input tube. I'd start with 100MF.

QUOTE=s-petersen;8304707]Here is the stripped down schematic,as it sits.
The amp could use a little more gain.
One amp has a 240 ohm cathode resistor,the other 330

[/QUOTE]

Edit:my comment above now seems redundant. I didn't realize that my wonderful high speed optima online connection dropped after downloading about half of the first page.

 

[s-petersen]

That's ok, if i tried that in the begining,I might have stayed with the original 6C4 base, and used 3 12AU7's in the final built.Thanks for the input,something for next time,if I need more gain.

 

[s-petersen]

The P6KE300A diodes work great for startup voltage limiting the preamp tubes. with all tubes pulled = 530v unloaded, the preamp sockets see 305 v the diode doesn't get hot or anything.I will add it to the schematic.
There is no current flowing in the diode below 300v.