Leach amp problem

[Ed LaFontaine]

After several years of good service as a sub amp, my Leach amp began to produce a low-level hum in one channel. This hum continued to develop and increase to unbearable levels. I've replaced the diode bridges (dual mono) with no improvement. I know I have a problem...with no input signal, the affected channel drives the woofer cones to full extension (outward) along with a hum. Looks like a DC signal to me. What should I check, the ouput transistors? And how?
Thanks

[Ed LaFontaine]

I will solicit some help from Prof. Leach

[jackinnj]

Mongo check for bum filter capacitor???

(also, check for dirt and grease on the board)

[Ed LaFontaine]

jackinnj was correct about the bum filter caps. I changed them to a set of 50V. I consider this temporary and will upgrade to at least 63V.

Thanks Jack!

I then discovered a ground loop. Prof. Leach's rec's were to use a CATV isolation transformer and remove all but one of the 3-prong grounding plugs in the system.

Works fine! This was the first time I had encountered a ground loop-so I didn't know anything from experience. A web search provides a bounty of info.