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  1. Jesco

    Zobel Filter

    My early 60’s Alamo Challenger (essentially a grid-leak biased 5F2a) has a conjunctive filter in the circuit.
  2. Jesco

    12" speaker recommendation for 5F2-A build?

    My 5F2A has a 4ohm 12A125A in a 5e3 sized cab. It sounds fantastic. I haven’t tried any other speakers with that build, but it really feels like a great fit for that amp.
  3. Jesco

    Ground bus detail

    This is how I do it on a PR. I also run a wire from the power supply ground to the pre-amp bus ground to create a single point grounding scheme attached to the chassis at the input.
  4. Jesco

    Completed Build: Torevibe with complex bypass switching system

    As a proud owner of a quiet torevibe, all I can say is “hell yes”! Well done.
  5. Jesco

    Continuous dropping voltage. 5f2a

    That’s exactly what I was thinking. I had the dropping plate voltage scenario happen on a fixed bias amp where the grid leak resistors had not been grounded. Something worth investigating.
  6. Jesco

    Revibe - Elevated Heater Center Tap?

    Learning opportunity for me! I don’t understand the above statement. They way I’m looking at it, if you connect the heater line center tap to the cathode of a cathode follower triode stage, you would be shunting 3.15 VAC into the signal path. What am I missing?
  7. Jesco

    Revibe - Elevated Heater Center Tap?

    I believe that wouldn’t work because the cathode of the cathode follower is the audio signal path. You would be putting AC heater noise into the signal path.
  8. Jesco

    Revibe - Elevated Heater Center Tap?

    This is what I did in my Revibe build. The grounding scheme as suggested by tubeswell will work great. It looks like he’s following Jeff Gehring’s example of running individual ground wires back to a buss bar. In my revibe build, I connected grounds together by filter cap (ala Blencowe’s...
  9. Jesco

    Revibe - Elevated Heater Center Tap?

    In a cathode biased amp, yes. In a fixed biased amp, no.
  10. Jesco

    Turning an old zenith tube record player into guitar amp

    it looks like the cathodes of two power tubes (I assume 6V6) are tied together to an unbypasssed resistor. There appear to be two preamp tubes, two power tubes and a tube rectifier.
  11. Jesco

    Princeton Reverb clone - reverb hum

    No build thread. This was a custom order amp I built for someone recently. After I built it, there was intermittent hum, specifically when turning up the reverb. Initially, I was worried about the reverb tank, and was able to change the level of hum by moving it around. However, in the end, it...
  12. Jesco

    Princeton Reverb clone - reverb hum

    I just finished a 22 watt Princeton Reverb in a head. The head is not particularly high. It is as quiet as you could want. I’ll add a pic so you can see the size. I think it is maybe 9”s high? So I wouldn’t automatically assume a problem with reverb tank being too close to the chassis. I had...
  13. Jesco

    Help with a ground wire 5F1 with a single ground bus

    It sounds like you’re narrowing it down to the input circuit. If you’re getting noise when you chopstick pin seven and eight of the one, don’t ignore that. That could indicate a bad tube, or cold solder joints at those connections. The first thing I would check is to make sure that the...
  14. Jesco

    Help with a ground wire 5F1 with a single ground bus

    Not particularly. Some manufacturers user 18 gauge for heaters, but others use thinner wire. Coaxial wire is shielded, so it shields the signal from noise. Usually folks put the 68k resistors right on the Jacks and then run the coaxial wire to V1A grid. You’ll find pics of this online. It’s...
  15. Jesco

    Build Amp Clone from Old Organ Parts

    The preamp tubes in the 6G2 are 12AX7s. You can just substitute 6SL7’s without making any changes.
  16. Jesco

    Help with a ground wire 5F1 with a single ground bus

    Hope any of this helps. You’ll get there Jerry!
  17. Jesco

    Help with a ground wire 5F1 with a single ground bus

    Nope. I mean “run one of the resistors from pin 2 and the other from pin 7 of the 6v6 and ground them at pin 8 (cathode).” As shown in the image below. It doesn’t matter where in the heater line you put the artificial center tap. So this method attaches the artificial center tap resistors to the...
  18. Jesco

    Help with a ground wire 5F1 with a single ground bus

    I would resolder the artificial center tap coming off the lamp. I don’t like the idea of a ground point hanging of a lose wire. The most convenient way to create an artificial center tap in a champ is to run one of the resistors from pin 2 and the other from pin 7 of the 6v6 and ground them at...
  19. Jesco

    Partially bypassed single ended power tube stage as a treble booster. Is it true?

    I thought cathode bias introduces local negative feedback, which should reduce treble. The bypass capacitor shunts high frequency to ground thus reducing feedback at high frequencies. This seems to go against your statement that the cathode bias would “cut the low end and boost the treble.” Am I...
  20. Jesco

    New Guy here - building BlackVibe 6V6

    I don’t know if I saw anybody mention this yet, but I would pull out the output tubes until you verify that there is sufficient negative DC voltage on the grid of the power tubes. Otherwise you may burn up some 6V6s.
  21. Jesco

    Build Amp Clone from Old Organ Parts

    I think this is great advice. BTW, the output transformer was built for 6L6 tubes so it should work just fine. Lastly, because of higher wall voltages, with solid state rectifier you will get quite a bit higher B+. You might want to just test that power transformer with a solid-state...
  22. Jesco

    confused about 220k mixing resistors ab763

    I know Rob Rob has addressed this question in his AB 763 single channel Blackvibe schematic. I would reference his schematic. https://robrobinette.com/RR763_BLACKVIBE.htm Also, straight from the horses mouth, “The 220k resistors function as mixing resistors to prevent interaction between the...
  23. Jesco

    Two different preamps (one octal and one regular) in a Tweed Delux "clone"

    I would also add here that I don’t necessarily think we should direct people to seek the help of Rob. He has given an extraordinary amount of his time to the amp building community, and I think we should let Rob decide when and where he wants to jump in on a project. There are a lot of brilliant...
  24. Jesco

    Zappa

    Peaches in Regalia.
  25. Jesco

    Two different preamps (one octal and one regular) in a Tweed Delux "clone"

    This is exactly what I was thinking! If you leave the PI as is, the switching would be a piece of cake. And though I am no expert on tube distancing, I would reckon you could fit another socket in the preamp section, no problem (the 12ax7s in my ao-35 ghia clone are awfully tight). That way, you...




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