65 Fender Twin Reissue - No Reverb

[MikeH]

I have a handful of rca connectors on my bench that are simply a plug with the tip soldered to ground. That way, if I'm trying to figure out why the reverb isn't working on a fender (or If I just want it always on and don't want to worry about the switch) I can just plug it into the footswitch and the reverb will be always on. Just to take the footswitch out of the equation.

[52 Bill]

Grounding the reverb pedal jack on this amp will kill the reverb return signal. The reverb is normally always on.

The fastest tank test that I use, is to turn down the reverb control and shake the tank. If you hear the crashing of the springs, you know that the recovery circuit works as well as the reverb output transducer. Then swap the cables and again shake the tank. If the input transducer is working you will still hear the springs rattling, but at a lower level due to the impedance mismatch.

[MikeH]

Grounding the reverb pedal jack on this amp will kill the reverb return signal. The reverb is normally always on.

The fastest tank test that I use, is to turn down the reverb control and shake the tank. If you hear the crashing of the springs, you know that the recovery circuit works as well as the reverb output transducer. Then swap the cables and again shake the tank. If the input transducer is working you will still hear the springs rattling, but at a lower level due to the impedance mismatch.

Oh right. I was thinking of the vibe switch. I never remember that until I try it out.

[Enzo]

It's OK, we forgive you, you are from Ann Arbor, after all.

[MikeH]

It's OK, we forgive you, you are from Ann Arbor, after all.

Hahaha... I'm actually probably the only non-UM fan in this town.

And I assume your are THE Enzo from Lansing that I've heard good things about? I have a lot of friends in Lansing, and they all take their amps to you. Small world!

[Enzo]

No, I am the other Enzo in Lansing. I am the one no one likes. But the good Enzo is pretty sharp...

[week end warrior]

fender twin reverb issue

Hello caught your information on the twin reverb not working. I have a grandson with an issue like this one. when the foot switch is on and you move the amp it rumbles but when playing the insturment through the amp nothing.
I was thinking of replacing the one 12AT7 tube before taking it to a tech 100 miles away and maybe take a look at the unit. Any suggestions for a novice Thanks

Did the service center say they fixed it? or did they just tell you what they thought was wrong inside? If you paid them money to have it fixed and it is not fixed, then take it back and ask that they set it right or refund your money. I run a commercial repair shop, and when I put my name on something, it works. But if by the time the customer gets it back home, if it is not working for some reason, I want to see it back here so I can determine why.

When you say black and green, that says to me the little wires inside the reverb pan. They break. When someone here asks about their reverb I will specifically refer them to the "black and green wires" inside the pan. Look inside your reverb pan, there is a jack near each end, and from those jacks will be little black and green wires running to the ends of the spring assemblies. A gentle tug on each will tell you if it is broken off or not.

The reverb has two parts - the drive and the return. Since you can bump the amp and hear springs crash we know the return side works. So the drive side or the pan itself is the problem. The 12AT7 and the transformer are only on the drive side. The return side uses part of one of the 12AX7s.

One imprtant factor is that the drive signal has to get from the amp chassis down to the pan. So take a pair of patch cords from your stereo system and connect in place of the existing cable.

The drive side is really a small power amp. The cable that plugs into the INPUT jack on the reverb pan will drive a small speaker. SO pull the cable from that jack on th pan and connect it to a luttle speaker for a listen. ANything there?

When you replaced the pan, did you get the proper type? 4AB2C1B? Well, xABxxxx anyway?

[Enzo]

Unless I am having another senior moment, there are two 12AT7s in that amp, the other being the phase inverter next to the power tubes. If so, then you can swap the two tubes. Whatever was wrong with it as a reverb tube would then be wrong at the powr amp, but any change tells you the tube was at fault.

But if you read enough reverb threads, you will find the most common problem is a bad reverb pan. The thing down in the bottom with springs in it. The reverb pan should be in a black vinyl bag screwed to the bottom. Extract the pan and flip it over. there are two jacks on one side of the thing. from each of those cables go back up to the amp chassis. But inside the pan, from the back of each jacck, should be tiny black and green wires. They break off. Either at the jack, or right at the thing on the spring ends. See if any are broken off.


Also, unplug the cable from the jack marked INPUT, and measure resistance at the jack. There should be a very low resistance. If it measures open, the pan is bad.


IF you need a pan, order one of the same type. Look on the pan for a number like 4AB2C1B. That is the type.

[Prairie Dawg]

This is a problem that any shop should have troubleshot in a few minutes. You have reverb return but no drive. Here's a little troubleshooting trick: plug a small 8 ohm speaker into the send jack going to the input of the reverb pan. I have one already set up with the RCA connector and cable. The drive circuit is a small Class A amp with an 8 ohm output, and doesn't care if it drives a reverb pan or a speaker. Do you hear signal? If so, then it's the pan. If NOT, then the possibilities are: drive tube, drive transformer, reverb cables (yes, it's agood possibility) and in a few cases I've seen, the 500pF coupling cap just before the drive tube (C13). I've seen them open, and also with broken leads.

The reverb circuit is one of the simplest things you'll find in any Fender amp-don't know why they had it a week and didn't get it straightened out. Customers hate s**t that doesn't work when they get it back.