# Princeton Reverb - reverb quit working



## Lincoln (Jun 2, 2008)

What do you look for when a reverb that was working well, suddenly becomes almost nothing? Cables are good, you can hear the springs in the tank loudly when you move the amp around, but the reverb is barely there. Replaced by a hum that gets louder as the reverb is turned up.

Anything sound familiar? common?


----------



## silvertonebetty (Jan 4, 2015)

First try a new tube . If it’s a new amp return it


----------



## keto (May 23, 2006)

silvertonebetty said:


> First try a new tube . If it’s a new amp return it


That's what I'd usually say too, at least the (12AT7, right?) tube. I forget what else is inside the spring box, could it have a cold solder joint or something?


----------



## jb welder (Sep 14, 2010)

keto said:


> I forget what else is inside the spring box, could it have a cold solder joint or something?


The wires coming off the jacks inside the tank get sheared off fairly often. You can do a visual inspection or check the resistance at the tank input jack. Should measure very low, a couple ohms.


----------



## tonewoody (Mar 29, 2017)

Revisit the RCA jacks to and from the amp chassis and tank.

I know you said you did this already.
The oxidization can be surprisingly stubborn on these connections.
Seriously, get the De-Oxit, clean / re-tork the plugs. You might need to do this several times.

Fader lube the Reverb pot while you are at it. 
*at this point, you might as well spray all pots, jacks and connections.... retention tube sockets.... buy a 6 pack, make an evening of it...


----------



## Griff (Sep 7, 2016)

Is this an older Princeton? 

As said, there are tiny wires inside the tank that come from the tiny transformers attached to the springs to the input/output. The spring area vibrates, the input/ouput does not and the wire is such a thin gauge that it breaks off. 

If that's the problem, it's a pretty easy fix if you have a soldering iron. The hardest part is stripping back the thin wire.

I'd be surprised if this was not the issue.

Here's a couple of pics of an old Deluxe tank I fixed.


----------



## Hammerhands (Dec 19, 2016)

Make sure the input and output are plugged into the correct sockets!


----------



## StevieMac (Mar 4, 2006)

Had you been using a footswitch previously to turn the verb on & off? If so, the sudden disappearance of that effect would make me wonder about the amp's switching jack. Otherwise, does anything change soundwise when you turn the Reverb pot up i.e. more noise, hum, hiss, etc? Depending on what you hear, that might make me wonder about the pot.


----------



## tonewoody (Mar 29, 2017)

Lincoln said:


> You can hear the springs in the tank loudly when you move the amp around, but the reverb is barely there.


If you hear the springs "boinging", the output of the tank is not the problem. 
Signal is either a) not getting to the tank input, or b) shorting out in the tank. 

If you have another amp with spring reverb you could do a quick hillbilly test. Unplug the PR reverb in/out, hook up the other. (be sure to unplug the AC on the "donor" amp. Technically, you don't need to but nothing wrong with being "extra safe")


----------



## Paul Running (Apr 12, 2020)

From Rob Robinette's website:
*Troubleshooting Spring Reverb*
The reverb driver tube is pushed very hard with high voltage in many amps so the tube tends to burn out sooner than all the other small tubes. A bad tube can also cause excessive hum in the reverb. *Swap out both reverb tubes* with known good tubes and test the amp.

*The reverb tank cable connectors (all 4 of them) can corrode* and cause hum, pops, crackling, weak or no reverb. Clean the connectors (male and female) with contact cleaner. Spray the male connectors and insert them into the female connectors several times. If the connectors are heavily corroded a toothbrush, small brass brush or steel wool may be needed to get them clean.

*Try another set of tank cables*. They can cause intermittent signal drop out.

Mixing up the reverb input and output cables will result in *very weak reverb*. Swap the cables at the tank and try again. If it doesn't help or lowers reverb volume then swap the cables back.

*The fine wires in the reverb tank are a common failure point* and they are difficult to repair. Replace the tank if any of the wires are broken. I'm a fan of the MOD tanks for around $20.

If you *bang on the side of the cab* with the power on and reverb turned up and hear the reverb spring crash you know the reverb tank's springs, output transducer and reverb recovery amplifier are functioning (the second half of the reverb circuit).

You can *switch the tank's input and output cables* and bang on the amp again. If you hear the spring crash (it will be quieter this time) you know the input transducer is working. After this test you will know the problem is upstream of the tank, which is the reverb driver circuit including the reverb transformer. Swap the tank cables back to normal.

*Loose transducers can cause funky problems*. If they are loose put some glue on them to hold them solid or just replace the tank. MOD replacement tanks are my favorites.

*Isolating the reverb pan with a pan bag, rubber grommets and foam padding between the cab and pan *can help cure reverb problems, especially those that occur at high volume and high reverb settings.

*Adding a noise cap to the reverb circuit* can sometimes quiet a noisy reverb. See this for more info.

*A weak or bad V4A (Reverb Recovery) cathode bypass cap can cause a reverb oscillation (squeal)* due to positive feedback between V4A and V4B (Vibrato channel third gain stage).

A bad pan ground can cause the *reverb intensity knob to add volume and gain* (add dirt). Check cables and cable plugs and sockets.

*Reverb Hum*
Try turning the reverb pan 180 degrees to reduce interaction between the power transformer and the pan's output transducer.

There are many reverb pan grounding schemes and an incorrect set of cables can lift the pan's ground or cause a ground loop. Look at your amp's schematic to verify what part of the tank and cables should be grounded and what shouldn't.

Temporarily clip a ground connection to the tank and see if that helps with the hum.


----------



## Lincoln (Jun 2, 2008)

tonewoody said:


> If you hear the springs "boinging", the output of the tank is not the problem.
> Signal is either a) not getting to the tank input, or b) shorting out in the tank.
> 
> If you have another amp with spring reverb you could do a quick hillbilly test. Unplug the PR reverb in/out, hook up the other. (be sure to unplug the AC on the "donor" amp. Technically, you don't need to but nothing wrong with being "extra safe")


that's what I was thinking too. If it makes noise when you jar it, the recovery system is working. Gotta be on the input side of the tank


----------



## jb welder (Sep 14, 2010)

One thing to add to the troubleshooting of the reverb drive side. Classic Fender circuits that run a reverb drive transformer have a tank with 8 ohm input (4AB type tank). 
So you can take the cable that plugs into the tank input and connect it to a speaker to test the reverb drive.


----------



## Lincoln (Jun 2, 2008)

jb welder said:


> One thing to add to the troubleshooting of the reverb drive side. Classic Fender circuits that run a reverb drive transformer have a tank with 8 ohm input (4AB type tank).
> So you can take the cable that plugs into the tank input and connect it to a speaker to test the reverb drive.


I did not know that. Thank you, great tip. I've often looked at those little reverb transformers and wondered if they would make a SE, 3 watt amp.

The rest of the story on this amp.
It's a PR I built, and mailed to Ontario. It always had really good reverb, tons of reverb, but very little reverb when it got to Ontario. Something got jarred. He said the packaging was undamaged, and I thought I packaged it really well. Anyway, I'm trying to diagnose it long distance style. Good times.

And yes, I am cured of any desire to ship amps.


----------



## jb welder (Sep 14, 2010)

Well, shipping makes it even more likely the wire in the tank is broken. I think some of the manufacturers even put foam in the tanks for shipping now for this reason.


----------



## Lincoln (Jun 2, 2008)

jb welder said:


> Well, shipping makes it even more likely the wire in the tank is broken. I think some of the manufacturers even put foam in the tanks for shipping now for this reason.


Makes sense
I measured a tank here, and asked him to check his tank. I got 1 ohm on the intake and approx. 275 ohms on the exhaust.  
Waiting to hear back from him.

I thought about the tank when I shipped it too. When you buy a tank, they come with foam. I remember the old Fender stand-alone units had a lever thing to hold the springs before getting mobile.
Frig.


----------



## Paul Running (Apr 12, 2020)

jb welder said:


> Well, shipping makes it even more likely the wire in the tank is broken. I think some of the manufacturers even put foam in the tanks for shipping now for this reason.


Yes and as you probably know a good reason why the Ampeg's had the locking system, it locks the pan to help prevent such issues...thanks for helping me with that issue that I had with my V2.


----------



## loudtubeamps (Feb 2, 2012)

Once you get the problem sorted, I would suggest a small dab of silicone on each end of the transducer wires at their solder/ entry points.....


----------



## Lincoln (Jun 2, 2008)

The tank measures good. 1.4 ohms on the input, 237 ohms on the output.
I asked him to try another RCA cable.

And he tried a 12AX7 in place of the 12AT7 reverb tube, didn't make any difference.


----------



## jb welder (Sep 14, 2010)

You know how the reverb driver tube and PI tube usually run very hot in classic Fender circuits?
Like, much hotter to touch than the other preamp tubes. If the reverb driver 12AT7 is not hot like that, it's probably not running. Could be it's plate resistor, cathode resistor, or the reverb drive transformer.


----------



## Lincoln (Jun 2, 2008)

jb welder said:


> You know how the reverb driver tube and PI tube usually run very hot in classic Fender circuits?
> Like, much hotter to touch than the other preamp tubes. If the reverb driver 12AT7 is not hot like that, it's probably not running. Could be it's plate resistor, cathode resistor, or the reverb drive transformer.


or a broken wire to one of the above things. Thanks for the tip on "heat". I never thought of that. 
I do know the reverb tube gets more volts than the pre-amp tubes do, but my mind didn't translate that into hotter.


----------



## jb welder (Sep 14, 2010)

I figured the guy you are remotely troubleshooting with is probably not a tech, so trying to think of simple things he can check. 
Aside from the cables you mentioned, probably running out of non-shop options.
This is an older unit, not re-issue? BF, SF ?


----------



## Lincoln (Jun 2, 2008)

jb welder said:


> I figured the guy you are remotely troubleshooting with is probably not a tech, so trying to think of simple things he can check.
> Aside from the cables you mentioned, probably running out of non-shop options.
> This is an older unit, not re-issue? BF, SF ?


Yeah, you got it.
It's a BF AA1164 that I built. Not recently built either. I've lent it out several times, played it lots myself, it always worked really well. I was confident in it. One of those builds that worked right from the start and never had an issue.

And of course I sold it for not even enough to cover the cost of the speaker, chassis, plates, transformers, and reverb tank., so I can't really say "take it somewhere and get it fixed, I'll pay for it"
which is what I'd like to do. The guy has been great about it too. He loves the amp, but he did expect the reverb to be working. I'm thinking of asking him to pull the chassis and ship it back to me. 
I gotta do something, I'm not going to leave him hanging.


----------



## Jerome (Dec 4, 2015)

Has the owner looked at the springs to make sure they haven't come loose ? Springs just seem to be the most likely fault , with cables second . Where in Ontario is the amp now ?


----------



## Paul Running (Apr 12, 2020)

Jerome said:


> Has the owner looked at the springs to make sure they haven't come loose ? Springs just seem to be the most likely fault , with cables second . Where in Ontario is the amp now ?


I agree and he could try a similar tank from another amp to verify it's not the tank...that's if he has an amp with a similar tank.


----------



## Lincoln (Jun 2, 2008)

Jerome said:


> Has the owner looked at the springs to make sure they haven't come loose ? Springs just seem to be the most likely fault , with cables second . Where in Ontario is the amp now ?


yes, he's had the tank out a couple times. Everything looks to be in place, and I got him to ohm the terminals, everything is good there too. I'm pretty sure it's not the tank.
As a final test, he's going to hook a speaker to the reverb input terminal and see if it makes music. He's in Pembroke.


----------



## Jerome (Dec 4, 2015)

Very good then . Best of luck sorting it out . Connecting a speaker to the reverb output jack on the chassis sounds like a good plan .


----------



## Paul Running (Apr 12, 2020)

Lincoln said:


> He's in Pembroke.


He's 50 miles from me...I live 4 miles from the town of Arnprior...if he ventures to Ottawa, I could take a look at it.


----------



## Lincoln (Jun 2, 2008)

Paul Running said:


> He's 50 miles from me...I live 4 miles from the town of Arnprior...if he ventures to Ottawa, I could take a look at it.


Thank you very much for the offer. We'll see if it comes to that point.


----------



## Lincoln (Jun 2, 2008)

Paul Running said:


> He's 50 miles from me...I live 4 miles from the town of Arnprior...if he ventures to Ottawa, I could take a look at it.


He's going to contact you Paul. Thank you


----------

