Fender Twin/pulling tubes

Discussion in 'Amps and Cabs' started by dlc1953, Apr 1, 2015.

  1. dlc1953

    dlc1953 Member

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    I got a Bf Twin with the 100/25 switch . Even with the 25 engaged its still about 2 on volume for playin in the house. Wanna pull the 2 inside tubes to turn it maybe to 4 or so. Do you really have to disconnect one of the speakers to be safe?
     
  2. cugel

    cugel Member

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    take a look at london power's website. i think in the FAQs. I would trust anything kevin o'connor says regarding this issue; most are wrong it seems. I pulled 1, 2, 3 tubes on a traynor 100watt and never touched the speakers and had great luck esp with 2 pulled.
     
  3. smolder

    smolder Gold Supporting Member

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    Was the 100/25 switch a mod or are we talking about an '80's amp?
     
  4. dlc1953

    dlc1953 Member

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    Ya 80's stock set up. This statement at Fender Guru got me thinkin.And don't know how it would apply if the switch is in the 25 mode? Pull out the two inner 6L6 tubes and you have a ~40-50W amp. You should/can also disconnect one of the speakers to not have an impedance mismatch. The Twin reverb output transformer is designed to work most efficiently with the following impedances/loads and tube power configurations:

    4 x 6L6 -> 4 ohm speaker load. And then comes the standard Fender +/- 100% tolerance.
    2 x 6L6 -> 8 ohm speaker load. And then comes the standard Fender +/- 100% tolerance.
    The plate voltage will increase a little when two of the tubes are removed. Ideally you should have the amp re-biased to not run the two remaining tubes too hard.
     
  5. swiveltung

    swiveltung Member

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    I don't know that model with the 25/100 switch. But normally you pull every other tube on a twin.
     
  6. Blue Strat

    Blue Strat Member

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    Yeah, I'd think that to get 25 watts that the switch is already turning off one pair of tubes...so pulling them won't make a difference.

    I'll see if I can find a schematic later.
     
  7. zenas

    zenas Member

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    I've done the two tube TR thing. If your trying to get it to distort at bedroom levels or even for most gigs these days it ain't going to help much.
     
  8. stucker

    stucker Member

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    I have the 90's Twin that has similar low power options:

    1) 100W/25W Switch

    2) 40W: Pull either the inside or outside 6L6 pair, switch the transformer from 16 Ohm load to 8 Ohm.

    3) 15W: do 1) and 2)

    My favorite mode is 2) or normal mode (for big stages/rooms). You will definitely get a lot more compression and reduced low end with 1) or 3).

    The power options really help that amp work for any situation. But it is a PITA to lift in and out of a vehicle!
     
  9. smolder

    smolder Gold Supporting Member

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    Sort of... On a SF/bf twin the power tubes are in pairs... Left, and Right. You want to pull the two inside or the two outside tubes, rebias, and ideally disconnect one of the speakers for an 8 ohm load.

    On the 80's amps, I don't know.
     
  10. dlc1953

    dlc1953 Member

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    This is what makes no sense to me. I have the Cougar 50w combo and had a Tweaker 40 . I could comfortably go up to 11 o'clock or so with volume but even with the 25 switch only 2 maybe 3 on the dial?? And when I go 100 still maybe 2(understandable there). Maybe somethings wrong with the switch? I mean the other amps are 1 /12'' but shouldn't make that much difference?
     
  11. dlc1953

    dlc1953 Member

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    Oh ya!!! Way to heavy. That's why I bought the other amp!!
     

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