Kustom Lead iii sc ombo - reverb issue - need schematic

[fredcapo]

I am working on a Kustom Lead iii sc combo w master vol, and ran into a reverb problem. I cannot locate a schematic and would appreciate it if someone can post it.

Anyway, the reverb was not working. The tank output jack was feeding into a working input, but there was a trashy signal feeding into the reverb tank input. Turned out to be a "bad" ground on the line coming from the circuit board into the tank. When i lifted the ground on the board side and connected it to the chassis the reverb worked. However there seems to be excessive hum - increasing proportional to cranking up the reverb pot- on the reverb channel when there is no guitar signal. Its a nice sweet reverb but I think there is too much hum.

Question is: should the braid of the input to the reverb tank be tied to ground or is the shield at another reference level?

thanks

[soundguruman]

I am working on a Kustom Lead iii sc combo w master vol, and ran into a reverb problem. I cannot locate a schematic and would appreciate it if someone can post it.

Anyway, the reverb was not working. The tank output jack was feeding into a working input, but there was a trashy signal feeding into the reverb tank input. Turned out to be a "bad" ground on the line coming from the circuit board into the tank. When i lifted the ground on the board side and connected it to the chassis the reverb worked. However there seems to be excessive hum - increasing proportional to cranking up the reverb pot- on the reverb channel when there is no guitar signal. Its a nice sweet reverb but I think there is too much hum.

Question is: should the braid of the input to the reverb tank be tied to ground or is the shield at another reference level?

thanks

That's a pretty common complaint.
It's pretty normal for hum in reverb to increase as you turn the reverb knob up. Especially in cheaply designed amplifiers...
The reverb tends to pick up 60 cycle AC field from the power transformer and other sources.
If you use RCA cables to move the tank further away from the power supply, you will hear it decrease.
Also, inside the tank, check for broken wires on the input output jacks, or on the coils.
Many times there will be a ground loop, according to the design of the tank and the amp...

[fredcapo]

Thanks. Great information. I appreciate it.

My shop - newly established - is in an emi-dirty environment and while I usually can account for noise coming in on the input was not sure how succeptable the tank was.

[soundguruman]

Thanks. Great information. I appreciate it.

My shop - newly established - is in an emi-dirty environment and while I usually can account for noise coming in on the input was not sure how succeptable the tank was.

Unplug the reverb and check w/ ohm meter to see if there is coil resistance on the tank input output jacks.
If the internal wire is broken or the coil is open you will see that as an open circuit on the in out jacks.
There can also occasionally be a bad driver, which will show ripple on the input jack, you will see a lot of 60 cycle on the input sine wave, etc...
but that's constant.
The reverb return is like a single coil guitar pickup. There is nothing to cancel external sources of hum.
So you can either move the reverb away from the power transformer, or make the power supply external...which is what has been done on lower noise equipment.
The minute you move that tank away from the power transformer, the hum is gone almost completely.