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  1. M

    Getting JMP 2204 bias in range

    I am using the Eurotubes tester and a Greenlee multimeter. Guy said they were new, only about two hours of play time.
  2. M

    Getting JMP 2204 bias in range

    Okay, another question. I just picked up a 2555 Silver Jubilee, it is marked USA on the tag inside. It has EL-34's in it, and guess what, biased very cold, 27mA I think. I was able to get the required number at the very end of the pot adjustment, 468v=37.3mA. With that being said, what is...
  3. M

    Marshall 1987T Tremolo '73 in the house!

    Sounded good. I don't see any type of master, how loud where you playing it in the clip? Had to be ear bleeding loud!!
  4. M

    Getting JMP 2204 bias in range

    Ok, thanks again for all the help!
  5. M

    Getting JMP 2204 bias in range

    Okay, thanks again for the info. Just did the piggyback of another 47k, and it seems to have worked. With bias pot all the way down, I was at 39mA, just a little turn got me up to the needed 42-43mA. Is there anything else I need to do or check, and will it hurt to run it like this without...
  6. M

    Getting JMP 2204 bias in range

    Okay, I think I get it now, Is that R30 in the circuit schematic? Is it the one next to the two 10uf caps? Funny, my Marshall book shows the 50w 2204 with the 56k resistor and the 100w 2203 with a 47k, but they are both EL34 diagrams, guess that is the difference? Mine has the 47k. I'll...
  7. M

    Getting JMP 2204 bias in range

    I meant to say parallel or piggyback the 47k on the existing, not series, for 23.5k resistance. What do you mean about swapping a 220k for 120k? Would it hurt anything to try the piggyback first?
  8. M

    Getting JMP 2204 bias in range

    Just found the resistor value calculator! Looks like his is in fact 23.5k, my scenario would be 19.4 as you point out above, way to little. i think I have a spare 47k that I will put in series and try 23.5k. If no good, then I guess remove 47k and start with 33k then 27k?
  9. M

    Getting JMP 2204 bias in range

    Yeah, I guess we will see. Another theory question, if his tech piggy backed on another 47k, does that in effect make it 23.5k?
  10. M

    Getting JMP 2204 bias in range

    Yes, I know how to work on them, solder, discharge, etc. MarshallDog, I figured this is all I would have to do. Just didn't know what value of resistor to piggyback. I have a 50w Metro Plexi clone that I was having the same issue with. I posted on the Metroamp forum same question and got the...
  11. M

    Getting JMP 2204 bias in range

    Yes, I bought it as you see it. It has the grid resistors, I think they are called, across the power tube pins, does that make it set up for EL-34's? What do I need to do to set up for EL-34's, change the bias resistor? Thanks
  12. M

    Getting JMP 2204 bias in range

    Sure here are a couple, let me know if you need more.
  13. M

    Getting JMP 2204 bias in range

    Also, any idea what is going on here with the added cable to V1?
  14. M

    Getting JMP 2204 bias in range

    I just gave that a try, no difference. Mine looks as it came with EL-34's, but who knows for sure, is there a way to ID that? Thanks
  15. M

    Getting JMP 2204 bias in range

    Hello, I am fighting the same issue on my '79 2204. I have plate voltage of 405 with EL-34's. I can only bias up to about 29ma. My calcs say about 43.2 (25 divided by 405= .0617 x .7= .0432). I have a 47k bias resistor that appears to be stock, I'm guessing I would have to lower that...
  16. M

    JCM 800 Died HELP!!!

    Turns out it was the 3 amp fuse, looked good but no continuity.
  17. M

    JCM 800 Died HELP!!!

    Yeah, I am going to get in there with a meter and see what's going on!
  18. M

    JCM 800 Died HELP!!!

    Was playing it yesterday and it sounded better than ever, today, no lights or anything. It is a channel switching amp, and nothing on the front works and no tube glowing in back. The fuses are good, and the wall outlet has power. Any idea where to start? TIA
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