Tweet
A friend just gave me a Marshall jmc 800 (2205). he said It worked but there was a loud buzzing noise. I checked it out and sure enough there was a loud buzzing noise. I touched up any suspect solder joints and replaced the power supply caps and put in a complete set of tubes. I Cleaned and tightened up all of the tube pins. I turned it on again and still have the buzzing. Here is a description of when it will start buzzing. With all of the knobs turned to zero there is no buzzing until you turn up the volume next to the gain then turn up the gain. I also noticed when I turned up the treble, middle, and bass it also effected the tone of the buzz. I changed the 3300uf filter cap in the preamp circuit and still I have buzzing.I also went around tapping all of the components with a piece of wood to see if i could locate any kind of a cold solder joint but nothing.
-
A friend just gave me a Marshall jmc 800 (2205). he said It worked but there was a loud buzzing noise. I checked it out and sure enough there was a loud buzzing noise. I touched up any suspect solder joints and replaced the power supply caps and put in a complete set of tubes. I Cleaned and tightened up all of the tube pins. I turned it on again and still have the buzzing. Here is a description of when it will start buzzing. With all of the knobs turned to zero there is no buzzing until you turn up the volume next to the gain then turn up the gain. I also noticed when I turned up the treble, middle, and bass it also effected the tone of the buzz. I changed the 3300uf filter cap in the preamp circuit and still I have buzzing.I also went around tapping all of the components with a piece of wood to see if i could locate any kind of a cold solder joint but nothing.
-
I'd start out by pulling the #1 preamp tube just to see if it makes the buzzing stop. If it does, that eliminates everything but the first two stages. (V1) If that's the case, after putting the tube back in, then I'd short the hot lug (right lug looking at the back of the control) of the preamp control to ground with a jumper. That won't short the grid to ground unless you turn the control all the way up. If you don't get any buzz, then the problem is between the input and the preamp pot. In that case, I'd clean the input jack and check the positioning of the 470k/500pf cap combo after the first stage coupling cap. Other than replacing parts after that, that's all I got
Comment