PCC85 in PRR Vari-Mu

Would it be possible (and difficult) to modify the PRR Vari-Mu to use these tubes? Besides changing the heater voltage, of course. Does it even make sense? I know PRR85 are used in Vari-Mu type compressors (Chiswick Reach, I think).

is the pin-out same?

Yes, the pinout is identical. I remember I put it in there once, but it distorted. So the circuit would at least need some adaptions to accomodate a different tube. But I don't understand enough about that to do it myself.  :-\

good time to learn some things.
is filament getting hot enough?
somebody here (bluebird?) posted his changes to the circuit:
higher plate voltage, different loading...

Can't find the schematic for the PRR Vari-mu. Do you have a handy link?

http://headfonz.rutgers.edu/comp5/Comp5.html

> I put it in there once, but it distorted.

Maybe it was carefully designed to suit 12AU7. Just as Chiswick carefully designed their unit for PCC85. You could design a fine limiter around a pair of 6L6. But not by bottle-plopping. Untold hours of plotting and figuring.

PRR said:

> I put it in there once, but it distorted.

Maybe it was carefully designed to suit 12AU7. Just as Chiswick carefully designed their unit for PCC85. You could design a fine limiter around a pair of 6L6. But not by bottle-plopping. Untold hours of plotting and figuring.

Click to expand...

Hahaha...couldn't help it man  ;D.

All right, thanks!  It's just that I like the PRR Vari Mu a lot, a second one would be build quickly and I've got some PCC85 lying around. Also, the compressor is pretty noisy (my build at least), so my hope would be to lower the noise with a different tube. No hum, just noise.
BTW, somehow noise above the audio band (of which my converters put out quite a lot at higher sample rates) ends up raising the noisefloor in the audio band significantly in the compressor. Could this be due to IMD?