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Vintage threads from the first ten years

previous: rooster Easy to design with less longevity.... -- 11/9/2003 1:57 AM

Re: MARSHALL 30th ANNIVERSARY - HELP!!!

11/18/2003 3:23 PM
Brad	Re: MARSHALL 30th ANNIVERSARY - HELP!!! Hi there chaps, Just sold my 6100LM to make way for a Bogner 101b. Luckily my 30th ann never had this problem, however I did see a friend of mine's amp do the same thing. It's most likely the bias voltage varying!! The way Marshall derive the Bias voltage for this amp is not in the conventional way (ie seperate tap of mains transformer). I can't confirm that it will be these bits but i have it on good authority that the coupling caps feeding the AC volts into the Bias circuits rectifier are responsible for the fault. Measure your bias volts to confirm this - note that sticking a 1 ohm resistor into the cathode circuits is a better way to set your bias aswell for this amp. good luck, Brad

11/18/2003 3:23 PM

Brad

Re: MARSHALL 30th ANNIVERSARY - HELP!!!

Hi there chaps, Just sold my 6100LM to make way for a Bogner 101b. Luckily my 30th ann never had this problem, however I did see a friend of mine's amp do the same thing.

It's most likely the bias voltage varying!!

The way Marshall derive the Bias voltage for this amp is not in the conventional way (ie seperate tap of mains transformer). I can't confirm that it will be these bits but i have it on good authority that the coupling caps feeding the AC volts into the Bias circuits rectifier are responsible for the fault.

Measure your bias volts to confirm this - note that sticking a 1 ohm resistor into the cathode circuits is a better way to set your bias aswell for this amp.

good luck,
Brad