Blonde Bassman channel differences?

Discussion in 'Amp Tech Center' started by schmee, May 19, 2020.

  1. schmee

    schmee Doctor of Teleocity Silver Supporter

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    Have you built a 6G6B? or do you have one?
    My build is sounding luscious, but the Bass channel has a bit of hum and it's like twice as loud as the other channel..
    I find zilch wrong with it except the voltage going to the red circle is very high... If you play through it you wont notice the hum, but when you stop you will. Volume at 0 will stop the hum.
    I don't really care that much as I don't intend to use the bass channel, but just curious mostly if the design has that in general or...? Not even sure why I built this amp except for giggles. Especially now with no summer gigs!

    Note: the Volume and Tone pots are all different values comparing the Normal vs Bass channel. That seems weird for Fender. Is that the reason for the huge volume difference between channels?
    [​IMG]
     
    Last edited: May 19, 2020
  2. radiocaster

    radiocaster Poster Extraordinaire

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    I have no idea if that's how it's supposed to be, but it has two triodes for the normal channel preamp and four for the bass channel, so it doesn't surprise me that it's louder.
     
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  3. Junior Little

    Junior Little Tele-Meister

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    That wire comes from the filter caps, right? I'd suggest the hum has something to do with the way the preamp filter caps are wired. For the higher voltage maybe check that the dropping resistor is not out of spec?
     
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  4. Intubator

    Intubator Tele-Meister

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    Have you tried swapping the 7025 in v1 with the 7025 in v3 by any chance? If the noise goes away on the bass input side but is then newly present in the normal channel, probably is the tube..
     
  5. schmee

    schmee Doctor of Teleocity Silver Supporter

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    I'll do that. I think I did it a while back but cant remember at this point. Would upping that resistor value reduce the voltage substantially I wonder? I also wonder if anyone with one of these has checked that voltage, maybe it's a glitsch in the schem....?
    I have done that, thanks!

    ----------------------------------------
    It's just hard to figure with both channels having such different value tone and volume pots, if that's it or the high voltage is it.
     
  6. Junior Little

    Junior Little Tele-Meister

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    I've built two, one used the PT from a Bassman RI and the other used the PT called for from ClassicTone. The Bassman RI voltages came out a bit higher everywhere in the circuit (~40V higher at the point you reference) and the ClassicTone PT delivered spot on voltages across the board.
     
  7. schmee

    schmee Doctor of Teleocity Silver Supporter

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    I built this one with a tube rectifier and used a Super Reverb style power transformer. Other voltages are very close. Go figure. At first I thought maybe I had that V1 P6 wire to the wrong Filter cap node, but AFAI can tell it's right.
    [​IMG]
     
  8. Junior Little

    Junior Little Tele-Meister

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    Is the voltage before the V2 plate load resistors the same as the voltage you're getting at V1 pin6?
     
  9. schmee

    schmee Doctor of Teleocity Silver Supporter

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    I'll check.
     
  10. radiocaster

    radiocaster Poster Extraordinaire

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    Some hum in this video, he cranks it to hear the hum, but it kind of sucks he doesn't do a proper demo with the bass and just hits a string.
     
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