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Post new topic Lowering the power of a Fender Twin/Q's on impendance
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Author Topic:  Lowering the power of a Fender Twin/Q's on impendance

Andy W. - Wolfenbuettel, Germany
Post Posted 2 Jun 2000 12:04 pm     Reply with quote

For some occasions I like to have my Fender Twin with less power, let's say 50%. Is it okay to remove 2 output tubes to achieve that ??

Another question is, if my 2x10" tube amp (Fender Super)has 4Ohms but an external speaker jack could I hurt the amp if I run a total load of 8 Ohms ??
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Donny Hinson

Glen Burnie, Md. U.S.A.
Post Posted 2 Jun 2000 12:40 pm     Reply with quote

You may remove the inside pair, or the outside pair of 6L6's to reduce the power. (I assume you want to "overdrive" the amp to get a particular sound.) If so, you can have a tech install a "master volume control" control somewhere on the back of the amp that would accomplish the same thing. It's not that tough a job.

Also, on your Super, can run the amp at 8 ohms, with a little loss of power (and maybe a slight tonal change) with no ill affects to the amp.
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Andy W. - Wolfenbuettel, Germany
Post Posted 2 Jun 2000 12:44 pm     Reply with quote

HI Donny

thanks for the quick reply.
Yes I want to overdrive the Twin but only for standard guitar use, I like to have it clean with the steel.
A mod would devalue the amp so that's the only way to go....
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Los Angeles
Post Posted 2 Jun 2000 5:09 pm     Reply with quote

Just to be safe, you may want to call or e-mail your question to Groove Tubes, Kendrick, or Torres Amps. I know in the Groove Tubes book it says that it's OK to do this for Marshalls, with the usual warnings about decreased tube life and other things. It also says to use a different impedance setting with the same speakers so that you can match the new "2 tube" output stage to your standard speakers. Even though tube amps are not supposed to be too fussy about their loads, since the Twin Reverb does not have an impedance selection you might want to make doubly sure on this, and make sure that you won't "hurt" anything. My gut feeling is that you probably won't, but just to be safe....

By the way, I have a 100 watt Carvin that I pull 2 of the 4 tubes out of. It is still more than loud enough in this mode.

You probably have already considered the other options available to accomplish this: a distortion/overdrive pedal, a power attenuator, or adding the master volume. The pedal and/or attenuator won't devalue the amp any since you don't have to do any mods.

The first Kendrick book also has several non-destructive mods for Fenders in particular that may accomplish what you want as well. If you have a fair background in electronics it would be interesting and informative to pick up a copy.
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Hamilton Barnard

Huntington Beach, CA
Post Posted 2 Jun 2000 7:05 pm     Reply with quote

Pulling out two tubes will cut the power output in half and will result in a 3 db drop in volume, which ain't squat. It will also increase what the output transformer will be looking for in the speaker load. On a Twin, that would change to 8 ohm instead of 4.

If the amp is biased on the "hot" side, pulling two tubes might put you in the danger zone.

[This message was edited by Hamilton Barnard on 02 June 2000 at 08:29 PM.]

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Dan Tyack

Olympia, WA USA
Post Posted 2 Jun 2000 8:55 pm     Reply with quote

Putting a master volume on this wouldn't give you the same sound as driving the power tubes harder. The first is preamp distortion, the second is power amp distortion. IMHO the second is way better. You might consider buying a THD Hotplate, which reduces the output to the speakers, but still gives you that sound. And it won't blow up your amp.

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Rich Paton

Santa Maria, CA.,
Post Posted 3 Jun 2000 3:15 pm     Reply with quote

On earlier Mesa-Boogies (1980's) with 100
watts, many models had a "half-power" switch.
The switch disconnected the cathode-to-ground connection of one pair of output tubes and essentially rendered the amp the same as a 60 watt version of the same model.
Since the power sections of the Mesa [non simyl-sync]amps is virtually identical to the classic Fenders, with the exception of fixed bias and the re-inclusion of the "presence" control, the concept shoulod work fine in a Fender.
The cathodes of that pair of tubes
are connected tohgether, and the switch is in
series with that connection and ground.
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