Fender Acoustasonic Junior (pre DSP) - reverb hum

[afm_380]

I have a second hand older Fender Acoustasonic Junior (pre DSP) that looks to be mint condition in which the reverb wasn't working. It sounded good, just no reverb.
When I dug into it I found the the reverb tank was plugged in backwards. When I plugged it in correctly it had a REALLY loud HUM and still no reverb, but at least in this configuration I could get sound thru the reverb circuit by brushing the springs of the tank. I purchased a new reverb pan and now the amp's reverb works. But's if the reverb is turned up to higher levels there is a noticeable to annoying hum. Not to bad if you play loud, but if you play with any dynamics the hum becomes annoying in the quiet sections. I don't have any experience with these amps ... Is the reverb section 'just' noisey on these, or is there possibly something else wrong in the circuit?

[52 Bill]

Is the pan mounted with the output side of the tank away from the power transformer? Ground the return plug's tip and then turn up the reverb control. Is there a lot of hum now?

[g1]

And how high settings on the reverb do you mean? Reverb springs will to a certain extent act as an antenna/pickup.

[Enzo]

And do you mean hum as in hum - the sound of touching your guitar cord? Or do you mean hum as in a low note WOOOOO sound that builds on its own when reverb is up?

[afm_380]

The pan is mounted in it's original position, which is fairly low in the combo cabinet away from the electronics. I'll play with positioning the tank in the cabinet, and check grounding the return tip, (it might take me a few days to get back ... thanks for the quick response, and suggestions).

[52 Bill]

The pan is mounted in it's original position, which is fairly low in the combo cabinet away from the electronics.

Yes, that's the right spot for it, but you would be surprised at how much difference there is in hum pickup if the tank has its' output side transducer mounted on the side closest to the power transformer.

[afm_380]

Thanks Again Guys for the suggestions and ultra quick responses (although my response here is unacceptably delayed .... ;op).

It's amazing how critical the pan placement can be with some circuits. I was able to find 'ONE' location within the confines of this combo cabinet that yielded 'acceptable' hum with the reverb turned to '12'. At normal playing levels the hum is only noticeable if you 'listen' for it.

Thanks Again for all of your assistance ...

[TimmyP1955]

It could be that it was plugged in wrongly because someone was 'messing about' trying to get an incorrect replacement tank to work (wrong grounding scheme and/or impedance(s). So make sure that the tank is the right one, not just the same as the one that was in it.