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Marshall 2031 100 watt tube power amp maintenance?

Discussion in 'Amps and Cabs [BG]' started by Engle, Apr 11, 2017.

  1. Grumry


    Jul 6, 2016
    If it's free, why not give it a shot?
    bobyoung53 likes this.
  2. 100w worth.
  3. GreaserMatt


    Sep 4, 2004
    Seattle, WA

    ha ha just kidding
    higain617, Miles_ONeal and bobyoung53 like this.
  4. GreaserMatt


    Sep 4, 2004
    Seattle, WA
    I'd rock it... : )
    Miles_ONeal likes this.
  5. For me it would be useless.
    bobyoung53 likes this.
  6. primusfan1989


    Jan 17, 2005
    new jersey
    I guess it depends on what kind of tone you're going for. For me 100 tube watts won't have enough headroom for me
    bobyoung53 likes this.
  7. lfmn16


    Sep 21, 2011
    charles town, wv
    For free, I would definitely take it and try it. For 'cheap' it would depend on what cheap means. If it's in good repair and good condition I'd probably risk a couple of hundred dollars on it figuring I could get my money back if I didn't like it.
  8. I think I'll pay $50 if it works. It may have been sitting unused for a long time so I would expect to have to replace the filter caps at least.
    lfmn16 likes this.
  9. I gig with a PF-50T and I'm ok with some dirt.
  10. Well I got it for free. I set it up in my garage with the door open in case of smoke. The numbers for 8 and 16 ohms on the impedance selector were rubbed off, but google helped me with that.

    I connected a cab with an 8 ohm JBL D130F, held my breath and fired it up. (I think the mains switch has been replaced and is upside down. The other switch is labelled HT, which I think should be the tube heater circuit.)

    There was a some 60Hz hum, and the smell of dust burning, but no fireworks!

    So I plugged in my Frankenjazz (with flats) to using the 1/4 inch input. I got some sound, but not very loud. That made sense as it is a power amp. I thought of using my line 6 bass pod pro, but it's mounted in a rack and I didn't feel like pulling it. Then I remembered my PF350 is designed to run without a speaker. I grabbed a XLR cable, but the line out on the PF350 and the input on the Marshall are both male connectors. I found an XLR to 1/4" cable and tried that.

    That worked - Holy tube tone! I started low and then cranked the gain on the PF350 (Master doesn't affect the line out, but I see from the picture I better turn that down before my daughter uses the PF350)
    Taking Marshall volume to 6 was as far as I wanted to go in my garage!

    So I'm thinking I could gig with this beast. My question for those who work on tube amps is:
    What maintenance would be recommended on this - given it's about 47 years old?

    Marshall 2031 with PF350.jpg
    GreaserMatt and e-flat like this.
  11. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    Nice power amp. You can also try slaving it, with a cab connected, to the PF-350 connected to another cab.

    Start with a good cleaning of any dust inside the chassis. Perform a basic maintenance which includes testing the tubes, clean the tube sockets, jacks, and pots with deoxit.

    Then go deeper. This is a rare amp, try to find a schematic. Hopefully it will have voltage references. Go through the amp with a fine toothed comb and identify what circuits are not performing up to spec.
    Last edited: Apr 15, 2017
    GreaserMatt and bobyoung53 like this.
  12. primusfan1989


    Jan 17, 2005
    new jersey
    The electrolytic capacitors are probably dried out and or leaking (possible cause of the noise), swap them out (however if youre not versed in tube amps you might want to bring it to a tech, those caps are the ones that hold the lethal voltages) and Id update it to a 3 prong cable if it wasnt already done yet
  13. e-flat

    e-flat Supporting Member

    Jun 15, 2009
    Washington State
    Oh, man... I'd be all over an old Marshall tube power amp! I'm looking for something like this to run with some preamp pedals (VT Bass, etc). Have fun, that's an awesome score!
    Miles_ONeal likes this.
  14. Thanks - I trained as an electronics tech and I have worked on tube amps, so I'm aware of the dangers. The original cord is a 3 prong, but the ground is snapped off so that's an easy fix.
    Finding a schematic might prove difficult, but I think it would be similar to the power amp section of a 100 watt Marshall guitar or bass amp of that era.
  15. I've got a lot of projects on the go, so if it ends up just sitting there after a while I might put it up for sale.
    And I'm just north of the border from you!
    e-flat likes this.
  16. e-flat

    e-flat Supporting Member

    Jun 15, 2009
    Washington State
    Awesome, and I'll keep my eyes peeled for a schematic for ya! :thumbsup:
  17. Martin Beer

    Martin Beer

    Dec 4, 2004
    It's an interesting looking amp. If it's going to get regular use, it would be worth checking whether it has screen grid resistors on the power tubes. A lot of older Marshalls didn't use them and they can be hard on the power tubes, particularly with new production tubes.
  18. Well I finally found some time to open it up for a look:

    The V4 socket has been replaced and there’s some white residue on the board as well as evidence of heat/smoke.
    The 12AU7s are RCA made in Canada. The EL34s are CGE made in Japan. V6 looks like it might have an issue?
  19. coreyfyfe

    coreyfyfe Supporting Member

    Nov 19, 2007
    boston, ma
    Addressing the switch question/comment from above - if it behaves like a standard Marshall then HT is high tension or high voltage. The mains switch powers up the tube heaters, the HT is your high voltage. In case you hadn’t already figured that out.

    Looks like the screen resistor on that tube socket near the heat damage/white powder area is a bit damaged, could just be exterior but I’d check it out while I was in there.

    Looks like the blue electrolytic caps in that area are potentially your bias supply caps? What is the black piece, is it a sliding potentiometer? Looks interesting.

    The outside of the tube glass looks a bit scratched. If you pull the cap up is the getter still silver?

    Really neat find for the price.
    Wasnex likes this.

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