My recent build is a little stiff...

50 watt or less OT would be where I would start. You could drop the B+ even more after that.

 

The problem is that the notes seem to decay pretty quickly. I know this is a function of the huge OT, the filtering and the huge power supply.

this has nothing to do with filtering or beefy power supplies.

 

Without being there to play it, I'm guessing you mean the stiffness associated with a big clean transformer, all other things being right. Less compression means quicker notes which I relate to transformers, filtering, voltages, etc.

 

stiffness and a note dying out aren't related.

An amp can be stiff and still have plenty of sustain.

 

Fast decay - at least at loud volume - can be owing to a signal polarity inversion (the sound vibration the instrument causes - feedback instead of +). (I once made a speaker-level polarity-reverse box just to see if it would make any difference - the change in sustain was big.)

 

It's usually a sign that there's some signal blockage somewhere. Signal is getting clamped down before it naturally fades.

 

Oh, you mean real stiff.

 

well you need to determine if the notes are being choked out or not.

stiffness will relate to the initial attack of the amp. As the filtering gets lower the relationship between pick attack and amp response will start to level off to the point where if you hit the note harder the amp will just sag and compress a little.

if your notes are choked that means that the amp is no longer amplifying the strings even when they are still ringing. That's a simple of something wrong in the amplification stages.

 

What's the plate voltage at all the tubes? Cathode voltages?

 

You might want to try for a lower plate voltage in the pre-amp by using a larger value dropping resistor in the power supply at that node. What component values are in your PI? Plate resistors, tail resistor, cathode resistor, etc. I've found I really like the Brown era values of 6K8 (tail), and 680 ohm (cathode) for adding some juice to the tone.

 

Lift the negative feedback wire off the output jack and see what happens.You may have too much negative feedback.

 

If the amp doesn't actually sound like something is wrong with it, I still think it could be the OT. It's huge, if it's the one I'm thinking of. No saturation there. It just sounds to me like it might be a big clean amp, like a Twin, only more so (OT). Did you reverse the speaker yet?