Swapping tubes questions

Discussion in 'Amps and Cabs' started by Tom Fontaine, May 23, 2019.

  1. Tom Fontaine

    Tom Fontaine Member

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    I recently got a used 5e2 modified circuit amp. It is made to take a 6550 power tube, and has a beefier transformer to presumably achieve 20w. Don’t know if it does, but it is fairly loud. Swapped in a cannabis Rex for the stock Chinese speaker, and it sounds nice even before breaking in.

    I have been having crackling issues with it so I checked the tubes. The power tube is not a 6550 but a sovtek 6L6. The preamp tube is unlabeled and the socket is not well attached to the chassis, it’s loose. It has a 5AR4 “made in China” rectifier tube.

    I’m clearly going to have to sort out the tube socket. I figure I might as well swap out all the tubes as well. I have no reference to identify the preamp tube but it appears to be a 12a?7. I’ve asked the guy I got it from if he knows, as well as a dealer of the amp. I am contemplating leaving the 6L6, but the 6550 is the tube it’s made for. I’d like the added volume from the 6550, but the 6L6 is going to be closer to that “tweed” tone right? Last question, I understand what the rectifier tube does and am wondering which rev tubes are best? I’d like to get the amp running hot, and really pump some sound from it.

    Any opinions welcome fellas.

    Edit : since the ampnis based on a 5e2, and I don’t believe the preamp circuit has been modified, it would likely assume a preamp tube for a 5e2 would be correct?
     
    Last edited: May 23, 2019
  2. Laurence

    Laurence Silver Supporting Member

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    Wow, that would be a heavily modified 5E2 to safely run with that power and rectifier tube. I'm not sure what to say, do you do your own work and maintenance? You can be pretty sure the preamp tube is a 12AX7 or a 12AY7 or possible a 5751. Any of those will work.

    The rectifier in the stock set up is a 5Y3GT, which is not nearly as stiff and demanding as a 5AR4; made in China or not. I would be suspicious that a modified amp suitable for a 6550 had a 6L6GC in it. Class A, but all the same - maybe the mod/trans really couldn't handle the 6550 in real life.

    Sounds like an interesting amp (speaker size?) and worth working it out. I'm not a tech and no longer have adequate eyesight to do the work I used to do. Start checking specs or take it to a tech you trust to map it out.
     
  3. Tom Fontaine

    Tom Fontaine Member

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    It’s a Tone Bakery amp with a 12” speaker.

    Now I realize the brand is questionable. Not many reviews of their amps, and plenty of discussion on their stompboxes. It wasn’t expensive though, and I figured why not. The wiring appears pretty good, and aside from the garage repair on the preamp tube socket, it’s build fairly clean to my untrained eye.

    Just going off the JJR site, 6550 is what it comes with. Between this and an “oversized output transformer” this thing is supposed to get 20w. I don’t care if it is or isn’t 20w, it sounds nice.

    I assume the rectifier tube is original, but I don’t know for sure. It hasn’t blown up yet, so.....

    Link in case anyone is interested https://www.jrrshop.com/tone-bakery-1955-tweed-princeton-clone-20-watts

    I think I’ll order a 12ax7, a 5751, and a 6550 (the 6L6 is still good, just a little corrosion on the pond that can be cleaned). Only question mark is the rec tube. I may just take it to the tech to give it a once over, but I’m also trying to learn as much as possible through this experience.
     
  4. HotBluePlates

    HotBluePlates Member

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    If the preamp tube socket is/was loose, that's probably the source of your crackle. Or connected, strained wiring (or possibly poor solder joints). While I can't rule out tubes being a source of crackle, it seems much less likely.
     
    Tom Fontaine likes this.
  5. Tom Fontaine

    Tom Fontaine Member

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    I’ll be at the hardware store tomorrow looking for the proper size nuts and bolts to get it back firmly connected to the chassis.

    And not I don’t do my own amp work. But that’s kind of the point of this amp. It was cheap enough, and simple enough to learn on. I DO understand the electrocution risks associated with amp repair. I am fully prepared to work entirely one handed.
     
  6. HotBluePlates

    HotBluePlates Member

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    IIRC, it's typically #4 nuts & bolts used to fasten a preamp tube socket. They're quite small.
     
  7. Tom Fontaine

    Tom Fontaine Member

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    Well I had to buy 100 #4 bolts and 100 #4 nuts, but I got that socket in there nice and snug. I found the mount at the rear of the socket didn’t even have a bolt, but a small screw that was in at an angle and touching the socket. Now I don’t know if this was the cause, or looseness in general, but I put proper machine bolts in and the crackle is gone.

    I think I’ll still order some new tubes though, just to experiment with how it affects tone. I got ahold of JRR shop and they said the amp is shipped and rated to handle the 5AR4 and 6550. I’m excited to swap stuff around, learn how biasing works, and hear what tones this thing can make.

    Thanks guys!
     

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