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Thread: Question on 77 Fender Twin Reverb

  1. #1
    Forum Member psalt's Avatar
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    Question on 77 Fender Twin Reverb

    Well I just purchased one, but I have some questions pertaining to all the stuff on the back of it. So here I go, any answers would be helpful as I have no clue about it..

    What is the outlet on the left for? (Not the cord, I'm not that stupid the thing next to it.)

    The a-off-b ground switch, what does it do and which position should I keep it in (I have it off now, that seemed safe to me.)

    What type of foot switch should I look into for it?

    The spot that says output tubes matching what is that for?

    How and what does the Hum balance thing work/do?

    When I get new tubes for it what kind should I get?
    How do you know when tube needs to be replaced?

  2. #2
    Forum Member Guildx700~'s Avatar
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    The outlet is an extra for pluging in stuff that needs wall voltage.

    The a/b switch is for hum, to change the ground on the wall power input.

    you need a Fender dual rca 2 switch unit, for reverb and vibrato.

    output tube matching is for biasing the tubes.

    If all is fine leave the tubes alone.

  3. #3
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    The ground switch may be set at any position safely. It is used to reverse the polarity of the wall plug for the least amount of noise.

    The outlet on the back may be used to power other small devices such as a plug in tuner, etc. Do not connect other amps to this socket though as they draw too much current. That is known as daisy chaining.

    The hum balance is used in place of two 100 ohm resistors to ground off the filament supply. It allows you to adjust the filament supply for the least amount of hum. Set the amps volume controls off and rotate the adjustment for the least amount of hum and you are done.

    The tube balance control allows you to "match" unmatched sets of tubes for better performance from the amp. At least that was the Fender engineers idea at the time. This system does not allow you to adjust the amount of current draw from each tube which is more important.

    You need a double footswitch with RCA connectors on each end. These are available from Antique Electronic Supply or many other sources on the net.

    If the output tubes sound fine then you won't need to change them. If you do want to change them out the new production 6L6EH from Electro Harmonix is okay. My favorites are the Ruby 6L6GCSTR.

    Good Luck,
    Tim C. :)
    Last edited by Tim C.; 07-27-2002 at 09:34 AM.

  4. #4
    Forum Member psalt's Avatar
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    thanks guys I posted on quite a few forums and no one answered
    Last edited by psalt; 07-27-2002 at 11:36 AM.

  5. #5
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    You're welcome!

    Enjoy this site. There are a lot of people here ready to help you when they can.

    Tim C. :)

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