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5G9 Tremolux Trouble Shooting

Discussion in 'Shock Brother's DIY Amps' started by jmp81sc, Dec 4, 2017.

  1. corliss1

    corliss1 Tele-Afflicted Gold Supporter

    Sep 13, 2008
    Lansing, MI
    I thought we'd established the problem was early on in the preamp since you8 can kill the noise by shorting the bright cap?

    Pull one tube at a time, starting from the preamp, until the noise goes away. Once it does the problem is either at or before that stage of the amp.

    Yes, if lead dress were an issue I would expect chopsticking to reveal something.
     
    jsnwhite619 likes this.

  2. Nickfl

    Nickfl Tele-Holic

    711
    May 24, 2016
    Florida
    Your lead dress actually looks pretty decent to me, the heaters have some room for improvement, but the signal leads look ok, so I doubt that's the problem especially if chopsticking isn't changing anything.

    Some of your solder joints look a bit rough and I'm wondering if that isn't the issue. I'm betting on a poor solder joint or a component that got cooked, did you heat sink the components (especially caps) when you were soldering? I'd go though it with needle nose pliers and gently but firmly test your solder joints. Don't try to rip components out or anything, but you should be able to firmly pull without anything coming looose and a poor joint will break free with little force. I'm thinking it sounds like it might be a loose solder joint somewhere in the preamp grounding.
     
    clintj likes this.

  3. jsnwhite619

    jsnwhite619 Tele-Afflicted Ad Free Member

    Sep 10, 2013
    Georgia
    Yep, in probably 99% of my buzzing issues (I'll leave that 1% in case I'm forgetting something) it was always due to a bad solder joint. As stated above, if you have found the cutoff point in the preamp that kills the buzz, start working backward and check you joints & reflow anything that is suspicious.

    The last buzzing like that I had that sounds like similar circumstances was where I had apparently bumped a connection loose on a tab off the volume pot while messing with the chassis out of the cabinet. It was my 5e3. I was playing with the negative feedback or something, but when I put it back in it sounded like a beehive. Of course, the problem was nothing to do with the NFB and the area I had been working -- it was on the opposite side of the board which took a WHILE to find.
     

  4. clintj

    clintj Friend of Leo's

    Apr 4, 2015
    Idaho
    It may well be early on, but the original grounding scheme was forcing all the current from the preamp, PI, and screens to flow the whole length of the chassis, through the chassis, to get back to its source. That's a good way to make the amp both a magnet for noise and a great broadcaster of noise for the preamp to pick up.

    So, the two caps feeding the output transformer are grounded to the PT bolt and the other two are to the bus? Good deal there then.

    I've looked through a few times now, and I don't see a heater center tap anywhere, either. I don't see a green/yellow lead, or a balancing pair of resistors led to ground. Is there one there that I'm missing?

    Just trying to snag any low hanging noisy fruit here. There's not a lot of spots, relatively speaking, for noise to sneak into V1. The grid, the cathode, and the plates + wiring to the controls is about it.
     
    D'tar likes this.

  5. jmp81sc

    jmp81sc Tele-Meister

    172
    Feb 6, 2015
    Orange County
    Hello all and thanks for your feedback.

    Pulling V2, the phase inverter tube, makes the amp go silent.

    I am pretty sure it is a bad solder joint or I fried a component during install, but I can not find it. I have reflowed the joints and pulled on them and changed the caps.

    Any suggestions for testing the caps and resistors? I tried using alligator clips to temporarily attach new caps in place with no change to the buzz.

    Thanks
    John
     

  6. jmp81sc

    jmp81sc Tele-Meister

    172
    Feb 6, 2015
    Orange County
    Hey Clint,
    I thought I had a heater center tap, but looking at the classictone specs for the PT I used there is not one.

    I will create an artificial center tap and see if that helps. I did not really understand the center tap thing until now.

    Thanks
    John
     

  7. jmp81sc

    jmp81sc Tele-Meister

    172
    Feb 6, 2015
    Orange County
    Hey Everyone and especially Clint,

    Thanks for all of your help, the lack of center tap on the heater filaments was the issue. Installed a center tap off of the pilot light and the amp is nearly silent.

    There is still a little hum, but I will spend some time chop sticking and redoing some of my lead dress, but overall I am really happy with the amp now.

    What is the mechanism for the lack of a center tap causing the loud buzz? Is it AC from the heater filaments getting on the grid of the preamp tubes?

    Thanks Again all for your help
    John
     
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  8. clintj

    clintj Friend of Leo's

    Apr 4, 2015
    Idaho
    Without a quiet reference point, a lot of transformer noise gets picked up in the heater winding and carried to the tubes.

    Glad that fixed it for you, and as always, glad to help.
     

  9. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    Great you got it fixed. Good job.

    Now remind me — have we seen this amp in a build or NAD thread? A 5G9 is a rare and beautiful thing.
     

  10. jmp81sc

    jmp81sc Tele-Meister

    172
    Feb 6, 2015
    Orange County
    No, I tend to be more of an active lurker. I still need to tidy up my wiring, drop the voltage down with some zener diodes and bias the tubes.

    I will post some pics when I get my cabinet done. I am going to try a more decorative cherry wood cabinet for this as a head unit, and also do a small combo cab out of cherry for my 5F2A at the same time.
     

  11. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    OK, but remember what's engraved over the Greek columns at TDPRI HQ: "Pics or it didn't happen."

    BTW, lots of us at Shock Bros. would love to see the chassis, board, etc. -- we don't do well with deferred gratification. Just post those here once you tidy up to your satisfaction. Then, sure, sound clips after the B+ and bias. Then, later, post an NAD in Amp Central when you have the cab done too. :)
     

  12. jmp81sc

    jmp81sc Tele-Meister

    172
    Feb 6, 2015
    Orange County
    Hey King Fan,
    I'll post up some more pics when I get it cleaned up, page one of this thread has some photos.

    The amp is still noisier than I would like, so I want to spend some time to refine it. Probably wont get much done until after New Years however.

    thanks for your input
    John
     

  13. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    Thanks, jmp. I'd missed those wider shots of the board -- that filter array looks smart. We'll stand by on your progress around clean-up and cab. :)
     

  14. Stratandtele

    Stratandtele Tele-Meister

    Age:
    45
    137
    Mar 31, 2016
    New Jersey
    IMG_0004.JPG
    You may be able to further reduce amp noise by running your filament wires "flying" style like the picture above. Run your leads off the board along the chassis to the pins of the tube sockets. Try to make wires cross one another at right angles. A lot of people have had successful noiseless operation this way. It keeps the noisy 6.3 volt a/c further away from sensitive signal wires. I also noticed pins 8 and 1 on your 6v6 are tied together and grounded with those long black wires. You might consider putting a grounding lug on your 6v6 tube socket bolts and grounding 8 & 1 there. Those long grounding wires can definitely pick up unwanted noise. Good luck with your build I hope you get it squared away.
     
    Last edited: Dec 14, 2017 at 2:37 PM
    King Fan likes this.

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