Dual Professional Reverb Problems

[locust]

I have a Fender Dual Professional amp that has a lot of noise in the reverb.The reverb works fine but when you turn the mix knob up it gets a loud whooshing noise and when the intesity knob is turned up it gets a loud warbbling noise.Neither has to be turned on paste 2 for the problems to appear.Can anyone help me trouble shoot this problem?I have some experience troubleshooting tube amp but please keep it simple.
TIA

[Chuck H]

The first thing I would do is try a "known good" tube in that socket. There are some other things it could be.Try the tube first.

Chuck

[Bruce / Mission Amps]

Not that this is your problem, but if you look at the schematic for this amp you'll notice that the poor 6V6 reverb driver is operating in class A at a ridiculously high voltage level.
The supply is right off the choke and the highest point in the B+ rail.
I usually mod these amps by breaking the B+ supply to the 6V6 driver OT with a 10watt 1k5 to 2K7 power resistor and new, 10uF/450v filter node in order to get the B+ at the 6V6 down to an acceptable level.
There is a good chance your 6V6 is already trashed from this high B+ abuse.
That noise could be the 6V6 screaming in pain.

[locust]

Thanks Bruce.Could you be a bit more specific as to where you put the resistor and cap.
Thanks

[Bruce / Mission Amps]

Thanks Bruce.Could you be a bit more specific as to where you put the resistor and cap.
Thanks

Yes... send me a .JPG or .GIF picture of the inside of the chassis and I'll mark it up for you.

[locust]

Thanks Bruce.Email sent with jpg.
Marc

[locust]

Could anyone help me out with the location of the dropponi resistor and cap.Have not heard back from Bruce yet.I'm sure he's very busy but I'd like to use the amp this weekend for a gig.
Thanks

[Alex R]

Well can't do a picture but maybe a bit of elucidation might help... what he means is the resistor and the + end of the cap both go to the side of the reverb transformer that currently gets the B+, which is the opposite end of the winding to the 6V6 plate. The - end of the cap goes to earth. Dunno if this helps but hey I tried.

[Alex R]

erm - and the B+ wire currently connected to the transformer, obviously take it off and that goes to the other end of the resistor, thus feeding in the B+ through the 10 watt resistor and dropping the voltage.

[locust]

So I added resistor and cap and got the plate voltage on the 6V6 down to around 336VDC.Thanks Bruce and Alex.Still have this whoooshing, lopeing
noise which is mainly affected by the mix knob.Any more ideas?
Thanks

[Jag]

Did you try Chuck's suggestion?

[locust]

I have tried a few new tubes

[Alex R]

Check the cable screens are connected to chassis ground, and that they connect the metal reverb pan case to ground.

Is there any reverb sound at all?

Do you still get the noise when you disconnect the reverb cables at the amp end?