SF Princeton Reverb Issue

[jaz761]

I recently purchased a 73 Princeton Reverb from the forum. It sounds very good to me but seems to have a reverb problem. The reverb sounds sort of "gated" and not lush or full. There is very little variation in the amount of reverb as I twist the knob. I had a 78 Princeton, I think, that had very nice reverb and currently have a 76 Super Reverb which has great reverb as well. There is also a high whistle, almost microphonic sound when the reverb is cranked on my new 73.

The original tank in my Super has been replaced due to corrosion in the original. I tried plugging the reverb from the Super into the Princeton and got no reverb at all.

I'd appreciate any clues as to what to look for.

 

[smolder]

Have you tried swapping out the middle two preamp tubes with known working tubes?

 

[jaz761]

I haven't..but I will try that tmrw morning.

That is exactly the kind of troubleshooting tips I am looking for. I've been playing through these things for too long without really understanding what's going on in there...trying to change that!

 

[jaz761]

I swapped out the two JJ 12AX7s with some different old 12AX7s I had sitting around and there was no improvement. I then swapped out the 12AT7 with an old tube I had around from a repair on my Super and that seems to have improved things. I still had the bit of whistle on high reverb settings. Swapping a 7025 seems to have cleared up the whistle too though just changing the 12AT7 made the most difference.

Would it would be worth buying some new replacements for the 12AT7 and the 7025 just to get off on the right foot with this Princeton?

The 6V6s are old tubes that sound good to me. One is a Crosley and the other is a Sylvania.

Any suggestions on good replacements for the 12AT7 and 7025?

 

[smolder]

I think it's always good to have spares for trouble shooting or failure. When I buy an amp, typically the tubes are not old stock... so those become the backup set for that amp and I try to re-tube with older, but good tubes (in some cases NOS). I also keep brand new (tested by the tube dealer) newer tubes just as a benchmark (6V6, 6L6, El84, and EL36)... but that may be overkill for many folks.

 

[TweeDLX]

Any suggestions on good replacements for the 12AT7 and 7025?

I really like the (NOS) Mullard 4024 for reverb and PI duty. Not really expensive, either. My only experience with 7025's is with the NOS stuff as well, so I can't recommend a current production tube.

 

[Dawg76]

I really like the (NOS) Mullard 4024 for reverb and PI duty. Not really expensive, either. My only experience with 7025's is with the NOS stuff as well, so I can't recommend a current production tube.

Bingo. I have a bought-new '76 SFPR (with tranny dates from '73, go figure) and replaced all its RCA tubes with the exception of the rectifier. On the recommendation from Mike at KCA, i replaced the reverb driver (V3 position) with the Mullard CV4024.
https://www.kcanostubes.com/content/nos-mullard-cv4024-12at7

I replaced the 7025 with a Tung Sol 12AX7 Reissue.

 

[WaltC]

https://www.thegearpage.net/board/search.php?searchid=33679985

lots of good info there...

 

[jaz761]

That link doesn't work...

 

[WaltC]

Sorry, it was a forum search for "reverb tank". Just select Forum search at the top right of the general "Amp Technical Info" forum and type in "reverb tank" or "reverb problems" or "reverb tank problems" or all of the above one at a time and you'll see lots of links to past discussions that include troubleshooting info, fix info and more.

 

[RedRock]

Occasionally. one of the two reverb tank springs will break off inside the
reverb tank. I suggest you pull the reverb tank out, remove it from the bag,
and check it to see if this has happened.