Got a 50 watt OTS head through 2X12 G12-65 closed back cab.  Love the tone, but I am really now refining my live application - which right now is chasing volume through the large jam build ups (classic rock based funky jam band).

I find that the PAB boost in the overdrive channel does not boost enough (a lot less than the clean channel) to dominate when I need it to.  I have a Kleinulator, and have tried a LBP1 (Electro Harmonix Linear Boost) in the buffered loop, but it reacts differently based on what else is on (3X volume boost when the delay pedal is on, and 2X boost when delay is off???).  Lately I have been manually twisting the send on the Kleinulator with my toe for solo boost (volume boost) and twisting it back post solo which is not a very elegant situation.  I have been considering a volume pedal in the loop as well - active I suppose.

But before I go buy more stuff, I thought I would ask you guys so that I don't miss something...

I am not sure if my trim gain is too high so the PAB boost is already nearly maxed, or if there is a circuit problem with my boost (it works in clean tones and does get richer in overdrive), or if I should turn my EQ down so the PAB is more differentiated, or try a volume pedal in the loop, or stomps out front?

I LOVE MY TONE, just can't dial my volume very easy on the fly.

As I understand it, the PAB simply bypasses the tone stack, which results in more signal getting through.  So its not really a true boost, you're just removing attenuation caused by the tone stack.
The difference in volume is less apparent in the OD channel than the clean channel because the OD signal is compressed.

The solution for you might be a clean boost pedal.  You could use it to boost the signal when engaged, or you can use it as an 'underdrive' - setting its gain low so when you disengage it, you get a 'boost'.   I don't use pedals anymore but I used to have an Xotic RC Booster and would give it a high recommendation.

. As jeffhamula stated, On the majority of the OTS amps, the PAB lifts the tonestack and removes it from the signal chain to a varying degree, depending on the model. In studying the layouts, each model seems to employ this lift a little differently, depending on the design of the stack and if the circuit has a mid boost or deep boost, etc and these little differences seem to allow for either more mids or high mids to get thru, depending on how it is employed. It seems only the BM does a full across the board lift, and, in the originals, employed a higher value resistor (22M vs 68k) resulting in even more boost. I have my PAB wired on a switch with 22M and 68k, and there is a huge difference.
In your case, I'd try a clean boost pedal IN FRONT OF the amp, not in the loop. I was using a Boosta Grande for a long time, and switched to the BYOC Tri boost. They both work very well, just different flavors

Sorry for the long winded explanation, and I hope this helps!

Gregg

I have all the parts and advice from Nik to do the slope mod, just have to find the time to do it.

As for tubes, I generally run late 50's/early 60's Long Plate GE tubes in V1 and V2, and a telefunken ribbed plate in V3 and in the c-lator. The Telefunkens are known for their toughness and long life, so I think they are perfect for the PI and the small space in the c-lator.Sometimes i run a JAN GE 5751 in V2 for a different flavor.

For output tubes I run either the Tung Sol "reissue" 6L6GC which offers a nice 5881 sound without worrying about redplating, or JAN Phillips 6L6WGB. The 6L6WGB is a small bottle tube, which is rated at a lower wattage (23-25) compared to a typical 6L6. It is a sweet sounding tube, I think mainly because it is on the razors edge as far as plate voltage and current is concerned. In the BM it really brings out it's raw tweedy side. the OTS the B+ voltage is just outside the range of the tube, so use with caution. I have redplated one once, but was able to shut her down before it went into full melt down.

Sorry for the long post again, but I hope this helps!

Gregg

I have tried different slope values on my OTS 50.
The original was 150K.
I was looking for a spongier, more compressed sound.

Had 68K in there for a whlie.
At first I really liked the change but after a while I wasn't so sure.
It was more spongy and compressed but was also a bit dull and made the tone controls much less responsive.
Currently using 100K which seems to be a good compromise for now.

Changing the slope resistor makes quite a big difference in the feel and response, so worth playing with.