Fender Princeton Reverb '65 RI

[keith_h]

I tried Jimmy J's suggestion, and sure enough by tapping on the power tubes with a small screwdriver (with the amp turned up just enough) I can indeed hear the sound coming through the speaker. It is more of a 'thump' on one, and more of a 'tink' on the other. Not really hearing much on the rectifier tube... very faint maybe.


So. There's that.

Just saw this. The tink or ringing generally indicates microphonic, the thump that it's ok.

[gtrguy]

Chopsticks are a great tool for amp work

[edwardofhuncote]

I tried Jimmy J's suggestion, and sure enough by tapping on the power tubes with a small screwdriver (with the amp turned up just enough) I can indeed hear the sound coming through the speaker. It is more of a 'thump' on one, and more of a 'tink' on the other. Not really hearing much on the rectifier tube... very faint maybe.


So. There's that.

Just saw this. The tink or ringing generally indicates microphonic, the thump that it's ok.

Fascinating. Thanks Keith. I would have assumed the opposite was true. Don't know if this matters, but when viewed from the back, the power tube on the right went 'thunk-thunk', the one one the left went 'tink-tink' when tapped. I wiped out and went to bed before I could disassemble the back and switch them around.

[edwardofhuncote]

Just to update and close out the thread;


The new tubes arrived in the mailbox today, and cured my Princeton. So now I know what to listen for in microphonic power tubes. Since they came as part of a matched set, I replaced all 7 tubes. Been playing for the past hour, putting the amp through paces. Good golly that thing sounds great. Hopefully that's the end of it.


As an added bonus, Thanks to Moderater Dave, I met some really nice folks right here in town who work on amps, if I need service in the future. They have some pretty cool stuff at http://www.uptownaudio.com


Thanks everyone for the helpful advice. 

[edwardofhuncote]

Part of the educational experience gained here... I picked up a really good deal on a fairly new '68 Princeton Reverb RI that had exactly the same issue, plus a cabinet rattle. It's similar to my '65, but a totally different voiced combo-amp. The '65 is a15w and 12" speaker, while the '68 is a 12w, 10" speaker, but same general configuration. This one had the same weird harmonic distortion on certain notes. I seriously think Fender might've got a wonky batch of GrooveTubes 6V6's.

Longer story shortened; guy was tired of fiddling with it, and even more frustrated than I had been with mine. (less patience, which is hard to imagine...  ) Anyway, Jimmy J's screwdriver tap-test confirmed one of the power tubes was suspect, and new matched pair of J/J's cured that weird harmonic warbl-ey racket. It also had a rattle in the cab itself on the lowest A notes. I snugged all the screws, put some small loops of gaffers tape behind the backboard, and that seems to have cured it. I have read where the front baffle boards in these (particularly the '68 RI's) are prone to rattle. Mine seems to be fixed though.

I like things about each of these Fender Reissues but I really don't need both the '65  & '68... two nearly identical combo amps... I may eventually have to decide which one to keep. I have this fuzzy feeling there is an F-2B in my not-too-distant future. I can envision a trade happening.

[rv_bass]

Nice job…I’d keep the 12” speaker