Fender amp reverb problem

[Rob Flinn]

Hi folks

I have a Fender Champion 30 amp on the bench. The reverb has stopped working. I`ve check that the signal gets to the tank & if I inject a signal into the return it is audible. Both coils of the tank show continuity.

Is there any problem that can phsically happen in the reverb tank ?? The springs don`t appear detached ??

 

[Guest]

Rob
NYD gave some good info on Reverb tanks in this Marshall thread
http://www.groupdiy.com/index.php?topic=3943&highlight=reverb

 

[Rob Flinn]

Ta Simon

 

[Gus]

this link is very good

http://www.accutronicsreverb.com/



Are there fet switches for the reverb on or off? If so I would check the power supply used for the switch circuit.

 

[Test Point]

Hi Rob,
I have found in the past, that even though a tank reads good continuity wise, it isn't always good. I can't explain it....maybe the little magnets in the pickup are "soft" or there is a short in one of the windings on the pickup coil (which would let you see continuity but....). Only when I replace the everb does it work again. Also, not to so great a degree in solid state amps, but if there is a DC level going into the tank, it will cause the tank to be weak or totally nonworking. I see that quite often in tube amps where the coupling cap gets leaky and applies a DC voltage to the input of the reverb tank, sometimes frying the input coil. Check to make sure there isn't a dc level coming out of pin 1 of U5....you'll still see the reverb signal but if it's riding on a DC voltage, the tank won't work right (or at all)...also check to make sure that the reverb control pot isn't broken...they use cheesy pots and the phenolic is prone to cracking.
Just some thoughts
Good Luck
TP

 

[CJ]

Slam the tank on the bench (well, not exactly a slam) . If you don't go deaf, your output from the tank is for sure too low,

 

[PRR]

> that the signal gets to the tank & if I inject a signal into the return it is audible. Both coils of the tank show continuity.

Be sure you didn't flip the input and output. Both ends work the same, but the impedances may be different enough that it does not work well enough to hear.

"Continuity" could be a dead short. Which does not work well for audio. Get numbers. Input coil could be 5Ω to 1K, pickup could be 1K to 10K.

Jiggle the tank. Does the amp "boing"? If not, yet the amp buzzes when you put a finger on the tank pickup pin, then the tank pickup coil is sick. If it has few-K resistance, then it may be demagnetized or something strange.

Likewise, power chords into the tank should cause visible jiggle. As mentioned, DC leaking into the coil can throw it so far offset that it hardly works.

 

[Rob Flinn]

Thanks for the suggestions.

Be sure you didn't flip the input and output.

I only removed the connections one at a time before replacing them, so I don`t think this is a possibility.

Continuity" could be a dead short. Which does not work well for audio. Get numbers. Input coil could be 5Ω to 1K, pickup could be 1K to 10K.

Was getting a few ohms from both coils. I seem to remember about 200 ohms.

)...also check to make sure that the reverb control pot isn't broken...they use cheesy pots and the phenolic is prone to cracking.

This is a possibility & I`ll try it tommorow. I don`t know if this is usual but the circuit shows that there is always a signal sent to thge tank & the reverb knob controls how much is returned. I suppose this makes sense because it would be less noisy !

 

[Test Point]

Rob,
How did you make out with this amp??? Just curious.
TP

 

[Rob Flinn]

Made a bit of progress but still not sure whether its100% right. Been busy with gigs & an install.