Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com

Super Bassman troubleshooting help

Discussion in 'Glowing Bottle Tube Amp Forum' started by PMELIUS, Aug 7, 2017.

  1. PMELIUS

    PMELIUS Tele-Meister

    120
    Nov 23, 2015
    Philadelphia
    Hey folks,

    I have an Earth B-1000 Super Bass - which is a near identical clone of a Fender Super Bassman.

    I'm cutting my teeth on the repair job for this amp, and I've done quite a bit of work (some necessary, some not). I'm at a point where I'm so close to being finished, but there's just this one weird little problem in my way.

    There seems to be some arcing in the power tubes. It's consistent across all 4 (6l6gc - JJ) and is responsive to playing. It's does not seem to be "blue tube glow" which I'm familiar with.

    I have it biased super cold right now (30 mA plate current), because if its biased any higher I also get this kind of flubbing out, almost oscillation on the decay of a note at higher volumes.

    My output tube voltages are all pretty much in line with what they should be. What am I missing?!
    Any help appreciated - see videos of symptoms below - thanks!

    <iframe width="560" height="315" src="" frameborder="0" allowfullscreen></iframe>

    <iframe width="560" height="315" src="" frameborder="0" allowfullscreen></iframe>
     

  2. PMELIUS

    PMELIUS Tele-Meister

    120
    Nov 23, 2015
    Philadelphia
    I uploaded another video with a hotter bias and it intensifies the condition

     

  3. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    IME, 30ma for 6L6 is not cold bias...it might not be hot but it isn't really cold. I am going to think that IF the plate voltages are correct, the tubes are dissipating somewhere between 40 and 50% of max plate dissipation.
    You don't say what you have done. IMe, if the electrolytics are original, I don't wonder about what is wrong. I change them. What are your voltages?
     

  4. PMELIUS

    PMELIUS Tele-Meister

    120
    Nov 23, 2015
    Philadelphia
    New electrolytics, as well as new matched power tubes. New/good preamp tubes. I've undone all modifications to the amp and replaced various components in the preamp and power amp. I've double and triple checked my work to make sure I have good solder joints and didn't make a mistake in my wiring. That's why I'm so lost because there is nothing that "stands out" as being wrong or a likely culprit.

    I should have specified that this first post is 30mA and 430v on the plate (under 50% diss.) In the 3rd video (2nd post) it's 43 mA and 459v on the plate.
     

  5. dan40

    dan40 Tele-Holic

    606
    Aug 19, 2015
    Richmond Va
    Are you absolutely sure that you have the amp set at the proper impedance for the speaker or speakers be used?
     

  6. PMELIUS

    PMELIUS Tele-Meister

    120
    Nov 23, 2015
    Philadelphia
    This amp is not switchable, it has a 4ohm OT and I am using the speakers in a Twin Reverb combo (4ohms) in these clips. How would that cause my issue?
     

  7. dan40

    dan40 Tele-Holic

    606
    Aug 19, 2015
    Richmond Va
    Impedance mismatching will cause arcing in the power tubes because of flyback voltage. Fender's seem to be a bit more tolerant of this condition but many a Marshall OT has been burned up from mismatching. It would be wise to double check with your meter. Just unplug your speaker lead from the back of the amp and place your meter leads across the tip and sleeve of the cable's tip. You should be seeing somewhere between 3 and 4 ohms if the speakers are wired properly. Any chance someone may have wired them wrong in the past?
     

  8. PMELIUS

    PMELIUS Tele-Meister

    120
    Nov 23, 2015
    Philadelphia
    Gotcha. I wired the combo myself and have tested it multiple times since. Definitely positive it's wired correctly at 4 ohms. The only thing worth noting based on what you're telling me is that these OT's have an 8 ohm tap which is unused, and just sits in the chassis. Not sure if they would add to my problem somehow?

    Edit: I should add that the 8 ohm tap is completely sealed and has no contact with any other conductive point in the chassis. It's just loose in there.
     

  9. dan40

    dan40 Tele-Holic

    606
    Aug 19, 2015
    Richmond Va
    As long as it is insulated well, the 8ohm will be fine laying inside the amp. During the repair of the amp, did you move or change any of the wiring inside the amp. From your description, you may have some oscillation going on. Sometimes just moving a particular wire a small bit will induce oscillation.
     

  10. PMELIUS

    PMELIUS Tele-Meister

    120
    Nov 23, 2015
    Philadelphia
    I had to replace a damaged output tube socket which required some rearranging of wires to get to, but I put them back to the best of my ability. This is definitely a possibility. I'm aware that coupling can happen pretty easily in the output section, but how can I go about troubleshooting that? Especially since the oscillation (if that's what it is) only happens on the decay of a note?
     

  11. PMELIUS

    PMELIUS Tele-Meister

    120
    Nov 23, 2015
    Philadelphia
    IMG_1057.JPG

    This thing is a mess in the way of lead dress
     

  12. dan40

    dan40 Tele-Holic

    606
    Aug 19, 2015
    Richmond Va
    I'm having trouble telling exactly what is connected to what at the power tube sockets. Does this amp have grid stopper resistors soldered right up close to pin 5 of every socket. Normal Fender value was 1.5k but it's ok to go higher.
     

  13. PMELIUS

    PMELIUS Tele-Meister

    120
    Nov 23, 2015
    Philadelphia
    Here's a little snippet of the schem. Each tube does have a grid stopper - 1.5k. If these were haywire, that could contribute to my problem?

    IMG_1061.PNG
     

  14. dan40

    dan40 Tele-Holic

    606
    Aug 19, 2015
    Richmond Va
    Just wanted to make sure that they were installed. They act to squelch oscillation and must be soldered right up close to pin 5 to work properly. I would try a fresh set of power tubes to rule them out but this issue may take a little probing with a scope to determine what is causing it. Does it happen with the volume set high or does it happen at all volume settings?
     

  15. PMELIUS

    PMELIUS Tele-Meister

    120
    Nov 23, 2015
    Philadelphia
    Unfortunately I don't have a scope - it's high on my want list.

    The blue flashing/arcing in the tube happens at all volumes, it's not until the volume/EQ is increased that it starts to flub out/oscillate on the decay of the note. The amp even sounds ALMOST good, but I still feel like the sound is being affected negatively by the symptoms.
     
    Bill Hubbard likes this.

  16. PMELIUS

    PMELIUS Tele-Meister

    120
    Nov 23, 2015
    Philadelphia
    Does this seem sufficient for the grid stopper installation? These are installed exactly as I received the amp.

    IMG_1062.JPG IMG_1063.JPG IMG_1064.JPG IMG_1065.JPG
     

  17. PMELIUS

    PMELIUS Tele-Meister

    120
    Nov 23, 2015
    Philadelphia
    Grid stoppers on my PI are 220k, schem calls for 1m. Voltage on grid of is 29, schem calls for 61. Would that contribute?
     

  18. Commodore 64

    Commodore 64 Friend of Leo's Ad Free Member

    Age:
    41
    Mar 1, 2010
    Kent, OH
    I think you mean grid leak, not grid stopper. And no, I don't think that would contribute.

    The fact that it's affecting all 4 power tubes would seem to me to eliminate individual components and values (like screen resistors or grid stoppers on the power tubes).

    Are your power tube plate voltages ~ 450 as shown on the schematic?

    I'm also not sure the "arcing" is arcing. Is there static, scratches and pops when the "arcing" is happening? Could just be gassy tubes.

    Are you measuring 30mA across each power tube cathode resistor? Or across what appears to be a 1-ohm resistor to ground off the bias pot?
     
    Last edited: Aug 9, 2017

  19. PMELIUS

    PMELIUS Tele-Meister

    120
    Nov 23, 2015
    Philadelphia
    Yeah last time I measured To bias the plates were at 459. The "arcing" I'm referring to can be seen best in the third video. Definitely could not be the best term, but I'm also familiar with gassy tubes and this is quite different, accompanied by unfavorable distortion and the oscillation mentioned. No scratchiness, static, or pop.
     

  20. Commodore 64

    Commodore 64 Friend of Leo's Ad Free Member

    Age:
    41
    Mar 1, 2010
    Kent, OH
    Are you measuring 30mA across each power tube cathode resistor? Or across what appears to be a 1-ohm resistor to ground off the bias pot?
     

IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.