The reverb on my Princeton Reverb Reissue was overpowering when I got it. Never played it above 3. The amp had a 12AT7 in V2 and 12AX7's in the V1, V3, and V4. When it came back from the tech after some hum-reduction improvements, I put a 12AU7 in V2 (I think my reasoning was to tame the reverb a bit). Also replaced the JJ 12AX7's with modern Tung-Sols. Played with it like that for a year. Then I noticed how weak the reverb was getting. In fact, full out at 10 it was downright puny. So I put the original 12AT7 back in V2, but there was hardly any change -- still a really weak reverb, so I'm thinking the tubes aren't the problem. The other 12AX7's in the amp are all near-new. I checked the reverb tank and cables and all looks good there. As an experiment, I put a 12AX7 into V2, and now the reverb is back to about 80% of the original depth, so I am happy. But will that 12AX7 in V2 cause any problems inside the amp? Thanks for any help.