Princeton Reverb Distortion

[coco]

I have read several posts on PR blocking distortion here and there that suggest a solution to nasty distortion at volumes above 6 or so, is grid stoppers from 10K to 1M on V2.
But how can this resolve the issue when you are not using Reverb? Or are these reverb specific issues?

[Willabe]

It can happen with the PI (phase inverter) on PR amps too.

Read this from our friend Merlin, it explains it and has a fix for it;
https://www.valvewizard.co.uk/cathodyne.html

[coco]

I have already included a 470K to the PI triode grid. I can try increasing it. Might have to break out the scope.

[coco]

when I unplugged the reverb tank, the OD seemed better. i had wired the plates of the reverb drive AT7 directly  not looping around the tube(which is a common thing to do). When I changed to a looped configuration, the OD with reverb tank plugged in, was pretty close to without, so, I will retest with a player.
Also  plan on putting in a 10K grid stopper on the AT7.

[stratomaster]

Nestled in Merlin's writeup is the silver bullet for this problem:

https://www.valvewizard.co.uk/reverbdriver.html

If you move the Reverb connection to the unused power supply node and reduce the 18k dropper to closer to 12k AND decrease the 2.2k resistor on the driver to 1.5k you will land near enough to the ideal conditions he outlines in this article. 

I've done this to a 68 Custom PR that I recently acquired and the results are terrific. Less hum from a better filtered node, more headroom in the reverb as the amp is overdriven, and a more usable reverb range from the slight reduction in drive. On the PCB amps you'll need to mind the grounding since you're moving to a new supply node, but on a clone everything is jumbled with the can cap so the fix is less practical.