Tube Amps / Music Electronics
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|10/3/2000 11:44 PM|
||weird reverb problem!|
Hope you can help me with this one.The amp is a 74 or 75 silverface twin reverb with master volume. the problem is a loud hum in the reverb,it is not feed back or oscillation it sounds almost like 60hz hum and it gets louder as I turn up the reverb control.Same hum with or without a guitar plugged into the amp.I've checked the obvious,tubes,reverb transformer, reverb pan everything seems ok.If I unplug the pan or switch off the reverb with the footswitch the hum all but disapears.The amp itself seems to hum a little louder than it should but with no change when I turn up the volume,it stays constant not like the reverb hum which increases as the reverb level is turned up.No the filter caps have not been changed butI can't see why they would only affect the reverb circuit.
|10/4/2000 12:43 AM|
You neglected to mention the Reverb/Tremolo footswitch/leads. Have you checked those? The fact that the hum increases with control setting increase sort of points to everything in the Reverb circuit path, so doesn't really help, but is nice to know. Remove the Reverb 'Send' and 'Return' leads and then turn up the Reverb volume control. Same problem? Then I'm stumped.
|10/4/2000 2:19 AM|
When I unplug the reverb send and return leads the hum disapears.IF I plug the input lead there is no hum but if I plug the output lead the hum returns.
|10/4/2000 4:12 AM|
I have found bad leads....shorted that did that same thing. Get out the VOM and check the leads.
|10/4/2000 10:30 PM|
OK! Now you've narrowed it down to the pan or the output cable. The hum to ME says the cable has a bad ground connection, but I can be and often am wrong, so try your meter first. I had a Twin that had a bad 'Send' cable that would cut in and out with the vibration of the amplifier intermittently! Drove the customer nuts.
|10/6/2000 2:52 AM|
have you checked the gounding of the grid resistor/cap at the return/output?
I just put a new tank in a 73 twin and it sounds like new. It was the tank in my case that was causing similar problems....
|10/4/2000 10:05 PM|
Do you have actual reverb signal with your hum? If not, I'd go after the wires or the tank.
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