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UL Bassman Mods

Discussion in 'Shock Brother's DIY Amps' started by Fred Mertz, Jun 17, 2016.

  1. Commodore 64

    Commodore 64 Friend of Leo's

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    Gigged it yesterday at a small musicfest in Kent, Oh. Weather made us go inside, but it was still a good time. 3 other folks played this amp throughout the day in their sets. So it was a real treat for me to hear others play, and not have it blow up or anything.

    I don't know if this is viewable by everyone or not but:

    I was using the Marshall Channel and my Dano.
     
  2. jonrpick

    jonrpick Friend of Leo's

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    Is there a direct link to the video? I got the page up. Didn't see a posted video.
     
  3. Commodore 64

    Commodore 64 Friend of Leo's

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    Try this one. I just snagged it from Facebook, someone else did the video.
     
  4. jonrpick

    jonrpick Friend of Leo's

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    Sounds great... Is that Dano a U2? I have one of the reissued U2s from 1998. It was a birthday gift from the ex-wife. I decided to rewire it for a parallel middle position instead of series. I'm thinking something grittier like a P90 would be good in there.

    Are yours soapbars or dog ears? I assume the latter.

    Either way, sounds great. Was that the EF86 or JCM800 channel? Sounds like with a slide and open E you could've gotten some really mean early George Thorogood tone.
     
  5. Commodore 64

    Commodore 64 Friend of Leo's

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    Yes, it's a U2 reissue. Not sure when it was made. It had a collapsed (ing) bridge when I got it, so I retrofitted it with aluminum stop tail, and added wilkenson brass compensated saddles that I had laying around. I also routed it out for P90s, and installed a simple vol/tone +3 way toggle. So it kinda behaves like a tele. But also like a dano with P90s, heh. It will handle the lowest action without rattling of any guitar I've ever owned.

    I imagine it would do a good Thorogood tone if the operator had any talent.

    So that was on the JCM800 Channel. I never stepped on a dirt pedal, I just used guitar volume knob.
     
    Last edited: Jul 24, 2017
  6. jonrpick

    jonrpick Friend of Leo's

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    I would love some details and pics of the P90 installation... even if you don't have any "in progress" pics from when you did it.

    I put an all-metal U3 bridge with adjustable intonation on mine.
     
  7. Commodore 64

    Commodore 64 Friend of Leo's

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    That's the only "in-progress" I have. I believe that pattern is from StewMac. I just used a flush cut bit to route it. That's double sided tape to mount it. I used a little Bosch hand trimmer to do it. A little easier to manage than my plunge router.
    [​IMG]

    Here's a shot of it on the wall.
    [​IMG]

    Found an "action" pic that someone took at a gig and posted to our facebook page.
    [​IMG]
     
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  8. jonrpick

    jonrpick Friend of Leo's

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    Looks great. Do you feel the body still has structural integrity after removing the wood? I've been inside a badly damaged U2 to see how it was put together. There's not much there, is why I ask...
     
  9. Commodore 64

    Commodore 64 Friend of Leo's

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    Yeah, I do. I made those mods in late 2014, and been gigging/practicing with it throughout that time. Like it enough that I recently traded my G&L ASAT Special for an acoustic guitar (since I didn't have one), so now it's my "number 1" inasmuch as I seem to prefer one guitar over the other. I'm more of an amp guy TBH.
     
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  10. jonrpick

    jonrpick Friend of Leo's

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    Good to know... I really think a pair of black P90s would look great in mine (it's also black).

    If I could find a Dano bridge in gold I'd upgrade the tuners and get gold screws for the pickups. Kind of a U2 Black Beauty look.

    Hijack off...
     
  11. Commodore 64

    Commodore 64 Friend of Leo's

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    OK, I got it on the bench.Something's up. Turned it on one day, and as it warmed up, I heard signal, then it dropped until very faint. Preamp propogates signal fine, I can clip the PI no problem. Bias voltage is steady, but cathode current is not. 2 different sets of power tubes slowly draw more and more current (still very faint volume in the speaker). I turned off the power when I was at 475 V on the plates and 118mA. Suprisingly the tubes hadn't red plated yet, but the temp of the glass was 450F!

    So..remember this is UL wired. Does it sound like the OT is the first place to look?
     
  12. Commodore 64

    Commodore 64 Friend of Leo's

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    With my DMM, signal generator, and 'scope, as near as I can tell, everything, including Lar Mar MV, power supply, and preamp circuit is operating normally. I think the next step is to take the OT out, subject it to the Neon Blink Test, and see what's what.

    Hopefully, it's as simple as a bad OT, though that will concern me...Why is it bad? This amp has been a tremendous pain in my ass since the moment I traded for it. But I really want it to work, I love the tone options of the JCM800/2204 and DZ. Rt 66 channels. I should note, that originally I tore into this amp in order to figure out why it had to be nearly dimed to play at small bar gigging levels. I wonder if the OT has been suspect the whole time?

    Is there anything other than the OT that could be causing my symptoms? BTW, the OT is cool as a cucumber under testing conditions.

    Similar symptoms, almost exactly, here (and it was the OT): https://www.thegearpage.net/board/index.php?threads/how-to-tell-if-my-ou...

    I ordered an Edcor CXPP50, 6.6k this morning: https://www.edcorusa.com/cxpp50-66k I would like to keep the UL Topology. CXPP are massive, and I have a CXPP30 I could swap in right now (it's as big as the existing OT in there). 8 week wait on the Edcor (who builds to order). Tempted to put in the CXPP30...
     
  13. Commodore 64

    Commodore 64 Friend of Leo's

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    I went through troubleshooting hell and a divorce since this post.

    Ultimately, the culprit was my cathode follower bootstrap circuit, sending 212V, and very low current (~2mA) to the original "Deep" slide switch on the front panel. That switch was leaking DC to the chassis. I bumped an input jack on the chassis, and I heard the guitar through the amp speaker, and I knew something was up. LOL. So it's all rewired, bootstrap is wired to a more substantial switch, and all is well.
     
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