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Old 13th October 2012, 04:00 AM   #1
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Default Reverb hum

Hey all I'm trying to get rid of this excessive reverb hum on my blackface Fender Deluxe Reverb that goes up with the reverb control. I looked at other forums addressing this sort of issue and I've tried to figure it out myself. So far, by pulling out the driver tube I see that the hum is still there so its not the tube. I pull out the recovery and I thought it took care of it but unfortunately it diminished the volume of the whole amp (meaning couldn't tell if it got rid of the hum or not). I tried maneuvering the tank but that doesn't seem to help. I'm at a loss here. Anybody have a clue what's going on?
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Old 13th October 2012, 06:17 AM   #2
rmyauck is offline rmyauck  Canada
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Only put one hand inside to measure high voltages so you don't make a path to the heart. May be safer to check voltages at tube sockets.

Has it been recapped? PS caps and coupling caps can cause hum and when they get worse take out a transformer. It happens in HI Fi amps so I imagine the same with guitar amps. Old caps leak a bit of voltage voltage causing the hum and of course when they really start shorting it's bad for the nearest components mentioned including tubes.

Lifespan is maybe 20 yrs max, but can be closer to 10. High temps lower life span. Ceramic (flat disk shaped) caps can last many years however.

If the caps are new and okay (you can get new caps that are faulty or been on the shelf too long)., maybe the control pot is faulty.

Check resistors also when recapping and clean tube sockets and tube pins. Voltages shown on schem. should be close though todays line voltages can bring them too high sometimes.

Check that grounding connections are good.

If everything above is kosher than swapping tubes is in order.

What's the "recovery" and what is "maneuvering the tank" ?

Hope that helps!


Last edited by rmyauck; 13th October 2012 at 06:31 AM.
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Old 14th October 2012, 12:24 AM   #3
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How will I check the voltages? Just attach one prong to ground and the other to the tube socket? I've checked voltages before but not on an amplifier.
Where should I check?

Yes the electrolytic caps have been replaced and the filter caps have as well.

The recovery is the 4th tube from the right, after the reverb driver tube.
Maneuvering the tank means that I moved the reverb tank around a bit to see if the location caused the hum. Tried moving it around, flipping it, rotating, taking it out of the cavity, but that all did not do anything to get rid of the hum.
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Old 14th October 2012, 08:57 AM   #4
M Gregg is offline M Gregg  England
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You need to find out if its on the input /output or Gnd.

ie what happens if you unplug the spring reverb? do you still have the hum?
If you do then its on the output section of the reverb circuit. By unplugging the reverb you have isolated the input driver<<I don't think it would be this.

If the hum is still there and only with the reverb turned up then its in the amplifying stage from the reverb.

Another good test is does the hum stop if you use the reverb pedal this grounds the input to the tube after the reverb ie shorts the tank to Gnd.
If using the pedal stops the hum then its probably a grounding issue.

M. Gregg
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Old 14th October 2012, 04:50 PM   #5
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It seems that when I unplug the footswitch the hum goes away for the unshielded lead, but is fine for the shielded lead. I don't know how I missed this. Should I just find a way to shield that lead or find a two conductor shielded cable somewhere and replace this with that? or do they make a reverb/vibrato footswitch that have both leads shielded so I could just buy it?
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Old 14th October 2012, 07:25 PM   #6
M Gregg is offline M Gregg  England
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Normally the foot switch is grounding the input to the tube after the tank.
So what you have is a cable coming straight off the tube grid high gain input which will hum like ---- if it's not screened. I can't see what you have so the point is to make sure the cable on the input to the tube grid is screened the other should just be Gnd.(The pedal is connecting the input from the tank tube grid to Gnd via its internal switch). So you have one hot sensitive wire and one at gnd..if they are connected wrong you will have a non shielded signal carrying cable...

You could just use a two core screened cable and make sure you have the metal pedal box grounded to the shield!

Ie at the jack end of the footswitch are the connections wrong? you only need one cable shielded the other is or should be Gnd?
so you realy only need a single shield cable the shield at Gnd and the hot wire inside it pedal to Gnd...if not shield both cables..two in one.

Hope this helps!

M. Gregg

Last edited by M Gregg; 14th October 2012 at 07:34 PM.
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Old 27th February 2014, 11:18 PM   #7
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Default classic 30 reverb hum

I just got myClassic 30 amp used on ebay a few weeks ago...quite reverb...but not i tried a couple of reverb tanks i had kicking around and it made no difference...but i did notice loud hum as reverb was turned up that wasnt there before...stepping on floor pedal stopped it, turning it down stopped it...went online found this and several other sites about same problem....after putting the origional tank back in for the 5th time...guess what...hum matter where i had the reverb knob its gone....just thought I'd pass this along....possible bad connection on the rca plugs (even though they were extremely tight)
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Old 27th February 2014, 11:27 PM   #8
kevinkr is offline kevinkr  United States
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Old guitar amp thread moved to Instrument and Amps per forum policy..
"To argue with a person who has renounced the use of reason is like administering medicine to the dead." - Thomas Paine
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