1968 Princeton Reverb, reverb not working

[Light Roast]

I just got a 1968 Princeton Reverb. Sounds awesome! Only problem being, the reverb isn't working.

I don't know anything about the guts of tube amps, and I'm far away enough from a real technician, that I'll either be troubleshooting this at home, or mailing it out for repair, which I really don't want to do.

It did not come with a foot switch. The tremolo works perfectly. When I turn up the reverb I just get increasing amounts of hum. The wiring is attached and not visibly damaged. When I tap the reverb tank I do get some quiet crackling, but not dramatic like I've gotten on the reissues I've owned in the past. The first tube is fairly loose in it's socket, but the others are tight.

Any suggestions on what I can do from here to troubleshoot the problem?

 

[corliss1]

A vintage 68? Does it have any type of service history?

You should get a nice splash from the tank by rocking the cabinet. If you have a multimeter you could measure the resistance of the input and output of the tank by simply measuring across the tip to sleeve of each RCA cable after removing it from the back of the amp. That will likely tell us if the tank is okay, and is a good first place to start.

But really, if you don't know the service history of the amp, it should see a tech.

 

[Light Roast]

Yes, it's a vintage 68.

When I rock the cabinet, there is a lot of loud cracking and static popping, with only a very small and quiet reverb splash.

The seller claims it was recently serviced, but I don't really know what that means. He also claims it was working when he shipped it. I'm trying not to point fingers, as I know these things can be fragile, which is one of the major reasons I don't want to ship it out to a tech. Nonetheless, I'm feeling like that's what I should do.

Anyone have any suggestions for vintage Fender amp techs in Arizona?

 

[corliss1]

Reverb tanks can go bad just by looking at them wrong, so that wouldn't surprise me at all if one got damaged in shipping.

 

[Blue Bill]

Check inside the reverb tank. Sometimes in shipping, a spring or transducer can get out of position. I got a new amp with a non-working reverb, it turned out to be a block of styrofoam in the tank, put there to protect things during shipping. Also test or swap out the RCA cables going to and from the tank, they can get stressed and fail.

Without a reverb pedal, I think the reverb footswitch jack on the back of the amp needs a shorting plug installed for it to operate. The missing switch acts like a reverb-off switch setting. Wiggle the tubes, there may be a loose pin connection. Good luck!

 

[corliss1]

Reverb doesn't need the pedal - trem does.

 

[iggyks]

And check the tiny wires inside the tank that connect the little transformers to the RCA jacks. They can easily break during the jouncing of shipping. I sold a few vintage reverb amps on Ebay and always stipulated that I either would put foam rubber inside the tank to keep the innards from bouncing and instruct buyer on how to remove it, or not be responsible for tank damage.

 

[BobbyZ]

Have tried another reverb driver tube? It's the 12AT7 that's always worth a shot. Another possibility is the cables from the reverb pan being mixed up, that makes um sound horrible.
If you have another Fender amp with reverb the tanks were all the same, plug it in and see if that helps.
Next up is the seller's claim it was serviced. I bought a lot of "serviced" amps that weren't. Oh they migh've had a few things done by someone somewhere. Outside of one I got from my brother, I never had one that was what I'd call serviced. There's no magic in old electrolytic capacitors, only odd noises and weird problems.
Never had a bad reverb pan on an old Fender, just got lucky I guess.
Oh the cables, if the shielding on them comes unsoldered it ain't good. Had a BFDR that picked up the local AM station once. Shield was loose right where the rca plug is on the amp side, easy fix. Lol

 

[Ten Over]

Reverb doesn't need the pedal - trem does.

Huh?

 

[corliss1]

Reverb is on by default - the pedal just shuts it off. You don't need the pedal to access the effect. You do need a pedal or a shorted RCA plug to engage the trem.

 

[abcdefghijklmnop]

Check the RCA cable that plugs in to the Reverb Input on the back of the amp. It could be bad. Also check the one from the Reverb Output.

I am having that problem on my Deluxe Reverb right now and I need to resolder the ground wires on it. The sleeve came loose on the cable, and the ground wires are exposed. As a result the reverb is working intermittently because the signal is getting sent to it intermittently due to the cable needing repair. Those old RCA connectors go bad all the time. Also clean the ends of them and clean the RCA sockets too.

 

[Michael Smith]

Are you able to remove the chassis from the cabinet and take some pictures of the circuit? We should be able to tell if it's been serviced. Also remove the "doghouse" cover and take a picture of the reservoir and filter capacitors. Don't stick your fingers inside the doghouse or the amp's circuit, because it can contain high voltage even if unplugged. If you are not comfortable working around amp circuits, then don't try any troubleshooting yourself inside the chassis.

Below is a picture of the capacitors inside the doghouse, showing old caps, from 1968 in this case. There is a date code on the caps that will read something like 235-6837. 235=Mallory, 37th week of 1968.

The doghouse is on the outside of the chassis, where the tubes are, a silver colored rectangular box, held in place by 4 screws. Once you remove the screws, if the caps are original, the cover may not come off easily, because there is a foam strip that may be stuck to the caps, but you can usually wiggle it off.

 

[AlbertaGriff]

There's no doghouse in a Princeton Reverb, there is a filter cap can.

OP, I definitely suggest carefully removing the reverb pan, and looking inside. I bought a 68 Princeton Reverb years ago that had the same problem. The teeny tiny wires inside the pan broke loose. Luckily I was able to fix mine with some solder, but that's not always the case.

Also, Corliss, I think Princeton Reverbs are different from other Fenders. Both the reverb AND trem work without a footswitch or RCA short.

 

[Michael Smith]

There's no doghouse in a Princeton Reverb, there is a filter cap can.

OP, I definitely suggest carefully removing the reverb pan, and looking inside. I bought a 68 Princeton Reverb years ago that had the same problem. The teeny tiny wires inside the pan broke loose. Luckily I was able to fix mine with some solder, but that's not always the case.

Also, Corliss, I think Princeton Reverbs are different from other Fenders. Both the reverb AND trem work without a footswitch or RCA short.

You are correct! Still early morning for me and my brain must be on standby still.

There may be a similar date code on the cap can.

 

[hepular]

You are correct! Still early morning for me and my brain must be on standby still.

There may be a similar date code on the cap can.

do the reissues have cap cans? or is everything internal on a board?

 

[Light Roast]

Thanks everyone for the suggestions. Tonight when I get home from work I'll pull out the reverb and take a look.

 

[zook]

Try swapping the reverb cables from input to output, they may be reversed.

 

[AlbertaGriff]

do the reissues have cap cans? or is everything internal on a board?

The filter caps are internal on reissues.

 

[Ten Over]

You do need a pedal or a shorted RCA plug to engage the trem.

You need a pedal or a shorted RCA plug to turn the tremolo off.

 

[schmee]

Thanks everyone for the suggestions. Tonight when I get home from work I'll pull out the reverb and take a look.

FIRST: Remove and clean the RCA jacks to the tank, especially the outside of the jacks on the amp itself!
As @zook said, could the cables be reversed? You just got the amp right? No harm in swapping them to see.