Reverb Problem on Reissue Fender Deluxe Reverb Amp

[Plato5v]

My reverb is only about a 10th of what it should. Even when turned to 10 there is only a small amount of reverb. I have checked the springs and the connections and these seem okay. When you shake the amp you do hear the reverb boom but when you plug in the guitar you only get a small amount of reverb. You can tell the difference when you turn it off or on with the footswitch but nowhere near what it should be. The tremolo works fine and the amp otherwise seems to have no problems.

 

I would appreciate any suggestions on what to do next or is this something only a professional technician can address.

[WRGKMC]

Looking at the schematic http://deluxereverb.waynereno.com/resources/AB763_Deluxe_Reverb_Schematic_Large.JPG you have a few options as a user you can try. One might be to change the one 12AT7 tube for a 12AX7 which might increase the output gain.

 

Second might be to try a different reverb tank. You'd want to be sure its got the proper impedance however. Tanks come with all kinds of coils for their inputs and outputs, so getting a match is important.

 

Beyond that you can modify the feed and mix, but that's better left to a pro. Fender reverbs are noted for their lush deep tones. I'm not sure what they did to the reissue but it sounds like its either being fed a weaker signal or the mix between dry and wet isn't strong enough.

 

 

You do need to know if its the input to the reverb that's low or the return mix is weak. If its the input to the tank that's weak changing the tube will make the gain stronger and may be enough to do the job. There is a 500 Pico farad cap that's in series with the signal that can be increased to allow more low frequencies to get to the tank, but springs don't like too much bass because they start sounding too pingy, so they are fed mostly mids and highs.

 

There is an impedance matching transformer after the reverb preamp tube which may be the cause of a low signal. Maybe they cheapened up on that part in the reissue build,

 

The best opportunity for increasing the signal may be on the output of the tank after the second preamp.

 

Between the preamp and tank you have a .003 cap. Increasing that caps value to .005 would feed more low frequency to the next stage giving you more lows. Then after the reverb level pot you have a 470 ohm resistor in series with the pot and a 220K ohm resistor in parallel to the pot. If you increase the 220K to the upper 200's or even low 300's it should let more reverb signal pass to the next amp stage.

 

What I'd do on a bench is just use a resistor and cap decade box that lets you choose the resistor values with switch combination and you can monitor the signal with a scope to make sure you get the best sound quality with the least amount of distortion. Again, this is how you'd do it on a bench. The cost of parts may only cost $1 and with the right tech (who may already know the circuit and knows what may improve it) can do this job in minutes.

[onelife]

A good test is to plug your guitar into the reverb return (marked as Reverb Output on the old Fender amps - I'm not sure about the DRRI). On a properly functioning Fender tube amp, your guitar will drive the reverb return circuit hard enough to get a normal (loud) output from the speaker. This will test the reverb return circuit but since you are getting the sound of the springs crashing then it seems that part of the circuit is okay.

 

You can test the rest of the circuit by plugging the output of the reverb tank (the lead that normally plugs into the reverb return) into the Normal Channel on the front of the amp. This is kind of a cool thing to try anyway because it gives you much more control of the sound of the reverb.

 

By performing these two tests you can narrow down the cause of your problem. Based on experience, my first guess is that one of the small wires that connects the transducers to the springs in the reverb tank has become disconnected or otherwise compromised. Before you haul the tank out of your amp it would be good if you could connect the springs in another Fender to your amp and/or your tank to another amp to help further isolate the fault.

 

[Plato5v]

Thanks for the comments.

 

My amp does not have a separate input plug for the reverb.

[onelife]

^^^ That's unfortunate - it's a good troubleshooting tool - the old amps were built to be repaired.

 

The re-issues may look and sound like the old Fender amps but they are a completely different different beast from a technician's point of view.

 

I really liked the old Traynor amps that had the chassis bolted into the cabinet on the sides. They used a separate piece for the top of the cabinet that could be removed with four bolts. The underside of the top piece had the schematic printed on it.

 

 

 

[WRGKMC]

^^^ They use the same schematic and component layout. I cant see it being that much different then an original other then some newer components here and there.

[Plato5v]

Again thanks for all the comments.

 

I took it to a friend's and he changed the tubes of the Reverb and it now is working.

[onelife]

Again thanks for all the comments.

 

I took it to a friend's and he changed the tubes of the Reverb and it now is working.

 

 

That's good news - the very thing that makes tuba amps great is also their weakness. It's always good to think in terms of tube problems first.

[Tube_Tonez]

Thanks for the comments.

 

My amp does not have a separate input plug for the reverb.

 

 

Glad you got it fixed. The reverb jack(s) is on the back panel. If it has the single 1/4" plug to reverb then this is a TRS, which carries both send and return. The vintage units had separate RCA jacks for each. You can test with an "insert" cable, which looks like a "Y" cable with one stereo TRS to two TS plugs.