1. Win a Broadcaster or one of 3 Teles! The annual Supporting Member Giveaway is on. To enter Click Here. To see all the prizes and full details Click Here. To view the thread about the giveaway Click Here.

Questions on variations of the blackvibe circuit

Discussion in 'Shock Brother's DIY Amps' started by zorgzorg2, Sep 19, 2020.

  1. zorgzorg2

    zorgzorg2 Tele-Meister

    Age:
    41
    Posts:
    310
    Joined:
    Feb 27, 2008
    Location:
    Norrköping, Sweden
    OK, so putting contact cleaner on the tube did help in that the crackling isn't as loud anymore. But it's still there when warming up. It's a Frondelli master volume I have, see the schematic above. I will check the soldering joints, I was getting the impression that my ground bus was a bit oxidised, so maybe the AC shunt caps or some bias caps could be having a bad joint indeed.
     
  2. zorgzorg2

    zorgzorg2 Tele-Meister

    Age:
    41
    Posts:
    310
    Joined:
    Feb 27, 2008
    Location:
    Norrköping, Sweden
    Tried again tonight, and the crackle seems to last much less now, maybe 2 minutes. So I think I can live with it. I checked all the solder joints connected to the master, can't see or measure anything wrong...

    Another question I have now: how do I dial the balance pot? I played with it a bit, but I can't hear much difference. The power tubes I have should be matched, so I should in principle dial it midway, right?
     
    sds1 likes this.
  3. zorgzorg2

    zorgzorg2 Tele-Meister

    Age:
    41
    Posts:
    310
    Joined:
    Feb 27, 2008
    Location:
    Norrköping, Sweden
    OK I read somewhere that it's about minimising the hum, but I can't hear anything...

    Another question about biasing. Robrob recommends measuring the ot voltages indirectly by subtracting each primary voltage to the ct voltage, but why not set the voltmeter directly between the ct and the primary lead?
     
    sds1 likes this.
  4. sds1

    sds1 Tele-Afflicted

    Age:
    44
    Posts:
    1,621
    Joined:
    May 4, 2017
    Location:
    Orlando, FL, USA
    Safety is why he recommends the other way.

    But measure the voltage across the OT directly as you say for better precision. Just be careful.

    50% is a good starting point, but you should be going by the numbers. It looks like you are working thru the bias procedure now. :)
     
    zorgzorg2 likes this.
  5. zorgzorg2

    zorgzorg2 Tele-Meister

    Age:
    41
    Posts:
    310
    Joined:
    Feb 27, 2008
    Location:
    Norrköping, Sweden
    Thanks @sds1! OK, I'll adjust the balance pot using a meter then.

    OK, back to the crackling problem. Tonight it didnt disappear after warmup. The crackle is sometimes mixed with white noise, in a fashion that reminds me of distorted amateur radio signals... Could it be possible that the amp would be catching these?
    How about adding an rfi suppressor cap, in case the noise comes from the mains lines? (they do have Internet signals on the mains nowadays)
    Setting the master volume to full doesn't actually remove the crackle, it just makes it very faint.
    Could a faulty ac cap I added on the bias circuits cause that kind of noise otherwise?

    Still investigating... o_O
     
    sds1 likes this.
  6. zorgzorg2

    zorgzorg2 Tele-Meister

    Age:
    41
    Posts:
    310
    Joined:
    Feb 27, 2008
    Location:
    Norrköping, Sweden
    One thing I noticed is that switching off the amp kills the crackle immediately, even if the guitar is still ringing. Would it indicate a mains issue?
     
  7. sds1

    sds1 Tele-Afflicted

    Age:
    44
    Posts:
    1,621
    Joined:
    May 4, 2017
    Location:
    Orlando, FL, USA
    Tube and bad solder joint still stand out to me as most likely culprits here.

    That's for both symptoms: the crackling and the sort of radio interference you are possibly hearing.

    This seems like a gremlin type issue, no doubt you'll solve it eventually (there is a solution to every problem inside the amp) but you could chase it for weeks. Let's avoid that if possible.

    If it were me, I would reflow every single joint in the amp and swap out all the tubes, either one by one or all together it doesn't matter. I realize those are both annoying next steps for their own reasons but, to me they are high on the list right now, to avoid leaving something obvious behind.

    I could be right, or I could be wrong! :)
     
    Last edited: Oct 31, 2020
    zorgzorg2 and D'tar like this.
  8. D'tar

    D'tar Friend of Leo's

    Posts:
    3,181
    Joined:
    Jan 11, 2013
    Location:
    WNY
    Use non conductive chopstick and push prod and poke every connection to try and manually duplicate the issue. Sometimes crackling can show as a light spark in a dimly lit room. Worth a look.
     
    zorgzorg2 and sds1 like this.
  9. robrob

    robrob Poster Extraordinaire Ad Free Member

    Posts:
    8,168
    Joined:
    Dec 29, 2012
    Location:
    United States
    The crackling is most likely a bad solder joint. Re-flow all the power tube and master volume solder joints.

    The bias balance is used during biasing to match the two power tubes bias current. Alternatively, you can dial in some intentional mismatch to generate some extra power tube distortion to fatten up the clean tone a little. Placing the balance pot mid-way is a good starting place.
     
    zorgzorg2 and sds1 like this.
  10. zorgzorg2

    zorgzorg2 Tele-Meister

    Age:
    41
    Posts:
    310
    Joined:
    Feb 27, 2008
    Location:
    Norrköping, Sweden
    Thanks guys for the good advice! I'll start reflowing some solder joints then. I poked around with a chopstick already but couldn't find anything suspicious. I'll dim the lights tonight to check for some arking. Regarding tubes, I don't have an extra set, I'll start hunting for those now.
     
  11. tweedy_woodpecker

    tweedy_woodpecker Tele-Meister

    Age:
    49
    Posts:
    143
    Joined:
    Jun 25, 2019
    Location:
    Austria
    Another vote for a bad solder joint. if you can pull the PI tube and still hear the crackle it must be somewhere in the power amp.

    I had the same issue a while ago and it turned out to be a bad solder connection of one of the filter caps to ground.

    As mentioned pulling tubes starting from V1 is often a first step to finding the origin of the issue.
     
    robrob, D'tar, sds1 and 1 other person like this.
  12. zorgzorg2

    zorgzorg2 Tele-Meister

    Age:
    41
    Posts:
    310
    Joined:
    Feb 27, 2008
    Location:
    Norrköping, Sweden
    OK, so I removed the tubes one by one, and the crackle seemed to stop when I removed v4. Then I went to put the tubes back, exchanging the power tubes placés, and when I went to put v2 back, I noticed pin 5 has stayed in the socket... I thought I was careful :(
    Anyway, now I need to order a new PI tube...
     
  13. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

    Posts:
    2,653
    Joined:
    Dec 30, 2019
    Location:
    california
    You may have found your crackle. lol.
     
    sds1 and zorgzorg2 like this.
  14. zorgzorg2

    zorgzorg2 Tele-Meister

    Age:
    41
    Posts:
    310
    Joined:
    Feb 27, 2008
    Location:
    Norrköping, Sweden
    Yeah, maybe indeed, if that pin was shaky from the start?

    Here the bad tube and broken pin
    20201101_181727.jpg
     
    sds1 likes this.
  15. sds1

    sds1 Tele-Afflicted

    Age:
    44
    Posts:
    1,621
    Joined:
    May 4, 2017
    Location:
    Orlando, FL, USA
    That has literally never happened to me.

    Should never happen!
     
    zorgzorg2 likes this.
  16. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

    Posts:
    2,653
    Joined:
    Dec 30, 2019
    Location:
    california
    It was just a TAD weak.

    :lol::lol::lol:
     
  17. sds1

    sds1 Tele-Afflicted

    Age:
    44
    Posts:
    1,621
    Joined:
    May 4, 2017
    Location:
    Orlando, FL, USA
    bwaa

    I bet the microphonics were super low before the pin fell off.
     
  18. zorgzorg2

    zorgzorg2 Tele-Meister

    Age:
    41
    Posts:
    310
    Joined:
    Feb 27, 2008
    Location:
    Norrköping, Sweden
    Haha, that will teach me to buy cheap tubes. Just ordered some jj instead for both preamp, pi, and power.
     
  19. zorgzorg2

    zorgzorg2 Tele-Meister

    Age:
    41
    Posts:
    310
    Joined:
    Feb 27, 2008
    Location:
    Norrköping, Sweden
    Alright, so while I'm waiting for a new set of tubes, I tried to go further on the crackle problem.

    Leaving the rectifier tube in, removing the preamp tube and just leaving the power tubes, the crackle can still be heard (v5 (rectifier) in, v3 and v4 in (power), v1 (preamp) removed and v2 (pi) removed)

    Removing v4: still crackle
    Removing v3: no crackle
    Putting back v3: crackle
    Swapping v3 with the other 6l6 tube: no crackle
    A bad tube?
    Removing v3, putting the "bad" tube in v4: crackle
    Swapping v4 with the "good" tube: no crackle

    Well well... Either I'm a tube breaker, or TAD tubes have a 40% failure rate in my case...
     
    D'tar and sds1 like this.
  20. BigDaddy23

    BigDaddy23 Tele-Holic

    Age:
    47
    Posts:
    674
    Joined:
    Jan 4, 2019
    Location:
    Australia
    Jeepers.....that’s no good if it’s the latter. Did you rule out bad/dodgy cathode or screen connections on the power tube sockets?
     
    zorgzorg2 likes this.
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.