Removing Tubes in a Twin Reverb

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by creekhed, Jun 12, 2006.

  1. creekhed

    creekhed Member

    Jun 12, 2006
    Ok...I am niether a Dimwit OR a Electronic Engineer... with that said...
    I want to reduce the volume in my Twin Reverb to get better tone in smaller venues. I was told to and implimented removing the 2 middle output tubes. This helped somewhat but the AMP is still very loud and I still cannot get the remaining tubes "saturated" enough to achieve the results I am looking for. I was also advised that Attenuators just plain suck and will suck my tone while trying to acheive my goal.
    1. Am I hurting the amp by running just 2 output tubes with no other mods (IE: impedence)
    2. Is there a way for ME to get my volume down similar to the "Half Power" switch in a TWIN (NOT Twin REverb) easily?
    I have read many threads regarding this issue but I am still not clear on the best ways to get better tone in smaller rooms with this beast of an amplifier.
    Any advise os much appreciated!
  2. AL30

    AL30 Member

    Jul 20, 2005
    Well... it's a Twin. It is what it is. Which is to say - it is VERY loud and very clean. The sweet spot on those is pretty loud too. Removing two tubes will help a little - about 3dB according to most techs. That's not much. You are probably not hurting your amp running with two tubes - as long as they are the inside pair or outside pair.

    Some time ago there was a post (Fender Forum?) about Twins and their volume and getting a decent break-up. Everyone had ideas and suggestions. The absolute best answer (and I apologize for not remembering who posted it) was "You are trying to make a cat bark".

    You are going to have a very hard time getting a "reasonable" volume and tone in a small venue it you consider a good tone power tube break-up. You're going to have to make the best with what you have or get a different amp for smaller venues. Start with a overdrive pedal (or rangemaster style boost) and work from there.

    There are a few tricks which will help a little with saturation.

    Run a 12AX7 for a PI - Most use a 12AT7 here. It's lower gain than a 12AX7. You can also run higher gain 12AX7's in all pre-amp spots. GT Mullards, JJ's or Tungsol reissues may be a good starting point.

    Remove V1 - First pre-amp tube furthest from Power tubes. You will NOT be able to use Channel 1 if you do this.

    Disconnect the Tremolo - Gotta get inside to do this - be careful.

    Run Hotter Power Tubes - Groove tubes rates tubes from 1-10 with 10 (I think) being the highest. Try those.

    If you have a Master Volume you can crank the channel volume and attenuate with the Master Volume. This will "override your main" and will saturate some and IMO sound like crap but it works.

  3. Dave C

    Dave C Gold Supporting Member

    Jun 10, 2005
    Waterford Ct
    +1 on Al's suggestions. You can also disconnect the tone stack using a push/pull pot for a significant boost but you may/may not like the tone....I don't. I'd at least try an attenuator, I've often noted that the amount of "tone sucking" is directly proportional to the level of attenuation you're if you only have to knock the volume down a notch or might be worth a try.
    Dave C
  4. creekhed

    creekhed Member

    Jun 12, 2006
    Thanks for the input!!!
    Hmmmmphhhh...sounds like I need a Vibrolux for the smaller venues;)
  5. John Phillips

    John Phillips Member

    Mar 17, 2002
    By pulling two tubes you aren't stressing the amp, but you are wearing the remaining two tubes faster because they are now running into half their matching load - the amp really wants to see 8 ohms now. You can cure this (and reduce the volume slightly further) by disconnecting one speaker, which will get you back to matching.

    A Vibrolux Reverb won't be significantly quieter than that - you'd need to go down to a Deluxe Reverb.

    That's effectively what you get power-wise with 'The Twin', which uses a voltage-switching scheme to reduce the power to one-quarter (25W). The way it does it also makes the tone a bit softer and squashier, which makes it cut through less well. You could fit this scheme to a Twin Reverb, but it's a tech job (though not an especially major one, and you could use the ground-switch hole for the switch, so you don't have to make it irreversible).

    Personally I don't think that attenuators sound very good with BF/SF Fenders when the power stage is driven hard, but you could achieve another 3dB reduction by running the attenuator as a dummy load connected to the Extension speaker jack - effectively a 'silent speaker' absorbing half the power. This is more tonally transparent, but will also wear the tubes a bit faster though since the amp is now seeing less than the ideal impedance again.
  6. Blue Strat

    Blue Strat Member

    Aug 2, 2002
    Sterling, VA (not far from Washington DC)
    Or maybe even a Deluxe Reverb.

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