MM 112 RD Fifty: Hum

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Author Message   Rainer Hackstaette Posted on Monday, January 06, 2003 - 11:02 am:    Hi, I`ve just acquired an MM 112 RD Fifty through Ebay. The amp works fine, except for a loud hum that is independent of the channel (clean/limiter) and of the setting of the volume and tone controls. The 2 6L6 are Groovetubes of uncertain age and glow normally. What is the cause of that loud hum? Should I replace the 6L6`s and the 12AX7? Could it be the caps or a transistor? Or even (please not!!) the transformer? The amp runs on 230 V at 50 Hz (I´m in Germany)and the frequency of the hum is close to the A note of a guitar (55 Hz). Please help - I´d greatly appreciate it! Rainer   TERRY Posted on Tuesday, January 07, 2003 - 10:51 pm:    A GOOD PLACE TO START IS TO REPLACE THE CAPACITORS. ALSO CHECK THE CERAMIC DISK CAPS ON TOP OF THE POWER TUBES. THE YELLOW CAPS ARE USUALLY OK. JUST DO THE MALLORY.   Rainer Hackstaette Posted on Thursday, January 09, 2003 - 04:15 pm:    Thanks, Terry! A friend suggested that the power tubes filter caps are probably the cause of the 50-cycle-hum. He´ll replace them for me. Thanks again for your help! Rainer