coupling cap question

[Bub]

Hi Gent's


I built a KOC Ampeg B15/ YBA-3 Custom Special. The original Ampeg uses a see saw splitter, I used a LTPI as on the schematic.
I took the Ampeg pre-amp and joined it to the YBA-3 power amp. The pre-amp has a 22n cap going to the volume, the YBA has a 22n at pin 7 of the phase inverter. I have looked for examples of these values on other schematics and cant find any. Voltages are good, sound is great but I dont know if it can sound better. Amp is very clean which is what I'm looking for. I see on a few Fender versions they use a 500pf cap at the phase inverter.
Tubes, 6SL7, 12ax7, 4 x 6550s
At full volume I have 9vac on the wiper of the volume control. 28 vac at the speaker jack. Clipping just starts to occur on my scope at 24 vac at the speaker jack.
Should I try a different value coupling cap at the phase inverter?
The schematic is just a cut and paste of both amps

Thanks for any help

Rob

[shooter]

sound is great

There's a song that says something about 1 step forward, 2 steps back
Is this a tinkering project or a gigging working machine?  That would be my determining factor

[Bub]

Tinkering project all the way.
I just don't know if I have the correct values to join the pre-amp to the phase inverter.


Thanks


Rob
 


 

[sluckey]

The LTP PI has a very high input impedance due to the bootstrap biasing circuit. That's why some amps use a 500pF input cap. But I also see .047s and .02s used quite a bit. There's no harm changing coupling cap values there, but a big-un ain't needed. Give 'em a try. Let your ears tell you which is correct.

You may even want to experiment with reducing those .1µF caps feeding the output tubes. Fender used that value on most of their amps but others use .047 or .02. The claim is to reduce some boom boom.

[Bub]

Thanks sluckey.


Rob