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Marshal Valvestate Model 8100 Trouble

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  • Marshal Valvestate Model 8100 Trouble

    I bought this Valvestate Model 8100 head new around 1992 (or so)

    I used it often then put it in storage about 10 years ago and recently had a need for it but when I powered it up, the output level seemed low and there was a loud hum.

    Thinking the hum was poor ripple from a Bad filter cap leaking through to the signal path, I changed C41, C40, C52 and C59. This didn't help, and actually the ripple was worse and the hum was still there, so I changed C40, and C41 back to the original Caps.

    Looking at the output signal, it seems that the Hum I am hearing is almost exactly a 250 hertz Sinewave... in poking around, I think I found a shorted cap (C42) and changed it but the Hum is still there.

    In an effort to fix this amp, I am going to change ALL the Electrolytic Caps and continue from there figuring that the age of the amp has something to do with old failing caps and I will get lucky.

    Am I chasing my tail with this amp or am I headed in the right direction to get this thing rockin' again?


    I'm attaching the Schematics for reference

    Thanks to anyone for some input.

    Attached Files

  • #2
    Valvestate Loud Hum

    Before you change anything, resolder the connections to the two main filter capacitors in the power supply. (C61 and C62, 2200uf/50V)

    Heat and suck out the old solder, make sure the caps are properly seated in place and then resolder them.



    • #3
      I forgot to mention, that C61 and C62 were the first caps I changed when all this first started. I changed those caps, and when it didn't fix it, I set the amp aside for a couple months until recently diving back into it.

      So the short of it is, they were recently replaced and are soldered in there well.

      Thanks for the reply


      • #4
        I know. This is a very very old thread.
        Someone might have the same issue though.

        My Valvestate 8100 head was just hum and nothing else.

        I changed all the big capacitors.
        In the end it was the two 1000uF 16V that fixed it. I was losing all hope because those where the last ones to replace and I thought it wouldn't make it. But it did

        Last time I heard working was something like 9 years ago!

        Back from hell.