Noisy/buzzing reverb tank
Posted: Fri Mar 19, 2010 1:17 am
Hi diy-ers, This is my first post here and thanks in advance for your time.
I have a 1970 Dual Showan that I recently had blackfaced by a local tech. Everything was working fine until I removed the chassis to look at the mod. When I put the chassis back into the head I started having a problem with the reverb tank.
With the amp ON and standby Off and all dials set to 0, when I sweep up the reverb pot a loud hum occurs and gets louder as I turn up the reverb dial.
Troubleshooting:
I disconnected the rca plugs and unscrewed the reverb tank and completely removed it from the head (i placed the disconnected tank and cables 3 feet away from the head).
Result = problem still occurs when sweeping the reverb dial. (all other pots are still on "0")
Next > With the reverb tank sitting outside of the head (2 feet from the head), I plugged the rca connecters back into the reverb in/outs.
Result = the noise is reduced (by 80% or so) when i sweep the reverb pot. pretty much back to normal.
Next > I then simply set the reverb tank (in the leather case), back into the head without screwing the tank to the head.
Result = The noise is bad again when I turn up the reverb pot.
Next > I then tried a different reverb tank from my 1978 twin reverb, tried all three scenarios above and the results were identical. (so its not the tank).
Next > I swapped out all preamp and power tubes and the problem still persists as specified above. (so its not the tubes)
Notes:
This amp has a three prong cord installed; however, every time I switch the toggle all the way to the left, I get shocked when I touch the toggle switch to flip it back over to the right.. (is this normal? this might be a separate issue entirely)
With the reverb set to 0 and all other dials set to normal settings (between 3-5 for vol/treble/mid/bass pots) there are no noise issues. Its only with the reverb pot.
Any thoughts about why this is occurring?
Thanks again, i have been searching a bunch of threads and could not find anything that was a good match for this issue.
Peter
I have a 1970 Dual Showan that I recently had blackfaced by a local tech. Everything was working fine until I removed the chassis to look at the mod. When I put the chassis back into the head I started having a problem with the reverb tank.
With the amp ON and standby Off and all dials set to 0, when I sweep up the reverb pot a loud hum occurs and gets louder as I turn up the reverb dial.
Troubleshooting:
I disconnected the rca plugs and unscrewed the reverb tank and completely removed it from the head (i placed the disconnected tank and cables 3 feet away from the head).
Result = problem still occurs when sweeping the reverb dial. (all other pots are still on "0")
Next > With the reverb tank sitting outside of the head (2 feet from the head), I plugged the rca connecters back into the reverb in/outs.
Result = the noise is reduced (by 80% or so) when i sweep the reverb pot. pretty much back to normal.
Next > I then simply set the reverb tank (in the leather case), back into the head without screwing the tank to the head.
Result = The noise is bad again when I turn up the reverb pot.
Next > I then tried a different reverb tank from my 1978 twin reverb, tried all three scenarios above and the results were identical. (so its not the tank).
Next > I swapped out all preamp and power tubes and the problem still persists as specified above. (so its not the tubes)
Notes:
This amp has a three prong cord installed; however, every time I switch the toggle all the way to the left, I get shocked when I touch the toggle switch to flip it back over to the right.. (is this normal? this might be a separate issue entirely)
With the reverb set to 0 and all other dials set to normal settings (between 3-5 for vol/treble/mid/bass pots) there are no noise issues. Its only with the reverb pot.
Any thoughts about why this is occurring?
Thanks again, i have been searching a bunch of threads and could not find anything that was a good match for this issue.
Peter