Are the channels on a 6G6 Bassman out of phase?

steven70steven70 Frets: 1262
edited October 2021 in Amps
Hello,
Anyone know whether the channels on a 6G6 ('blonde' bassman) circuit are out of phase?
Thinking of going into both channels. Could just use my ears I guess, but...
Advice appreciated.
Thanks
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Comments

  • Apparently it has 4 gain stages in the bass channel, two in the normal channel, so yes in phase. Jumper away, or use both channels.
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  • steven70steven70 Frets: 1262
    Nice! Thank you.
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  • ICBMICBM Frets: 71957
    telehack said:
    Apparently it has 4 gain stages in the bass channel, two in the normal channel, so yes in phase. Jumper away, or use both channels.
    Not quite as simple as that - the second stage on the bass channel is a cathode follower, which doesn't reverse phase. So there are three phase reversals on the bass channel and two on the normal, thus they're out of phase.

    It usually doesn't matter unless you have the channels set very close to the same volume though - you'll hear when is too close if you listen for the drop in volume.

    (Incidentally this also means you need to be careful with valve choice for V1 - Russian-made 12AX7s don't like being used as cathode-followers.)

    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • ICBM said:
    telehack said:
    Apparently it has 4 gain stages in the bass channel, two in the normal channel, so yes in phase. Jumper away, or use both channels.
    Not quite as simple as that - the second stage on the bass channel is a cathode follower, which doesn't reverse phase. So there are three phase reversals on the bass channel and two on the normal, thus they're out of phase.

    It usually doesn't matter unless you have the channels set very close to the same volume though - you'll hear when is too close if you listen for the drop in volume.

    (Incidentally this also means you need to be careful with valve choice for V1 - Russian-made 12AX7s don't like being used as cathode-followers.)
    Interesting. Sorry for the false info. I thought it was a matter of counting stages, each one doing a 180...
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  • ICBMICBM Frets: 71957
    edited October 2021
    telehack said:

    Sorry for the false info. I thought it was a matter of counting stages, each one doing a 180...
    It is if the output signal is taken from the plate - the normal configuration. With a cathode follower, it's taken from the cathode and is not phase-reversed. It's also technically not a 'gain' stage as the gain is slightly less than unity, but that's a different bit of pedantry . The purpose of this apparently useless no-gain stage is to produce a much lower source impedance from the valve compared to taking the output from the plate, which makes it much better at feeding a tone stack - hence why they're usually used for that. (Or driving FX loops.)


    "Take these three items, some WD-40, a vise grip, and a roll of duct tape. Any man worth his salt can fix almost any problem with this stuff alone." - Walt Kowalski

    "Just because I don't care, doesn't mean I don't understand." - Homer Simpson

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  • steven70steven70 Frets: 1262
    ICBM said:
    telehack said:
    Apparently it has 4 gain stages in the bass channel, two in the normal channel, so yes in phase. Jumper away, or use both channels.
    Not quite as simple as that - the second stage on the bass channel is a cathode follower, which doesn't reverse phase. So there are three phase reversals on the bass channel and two on the normal, thus they're out of phase.

    It usually doesn't matter unless you have the channels set very close to the same volume though - you'll hear when is too close if you listen for the drop in volume.

    (Incidentally this also means you need to be careful with valve choice for V1 - Russian-made 12AX7s don't like being used as cathode-followers.)
    I tried it earlier and noticed just that with the volumes, thought it was odd.

    Quite an interesting effect, jumping the channels...not sure if I'll use it for anything, but good to experiment.

    Thanks for the advice!

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