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Post subject: Pulling Tubes...
Posted: Mon Nov 19, 2007 1:36 pm
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Hey everyone,
Im new to the forum but im a fan of Fender gear and all so its about time I start posting!

Anyways, I have a Fender Twin Reverb that I had recieved a few years ago installed with 4 JJ Tesla 6L6GC tubes. I heard from a friend that if I wanna crank that amp that its possible for me to pull 2 of the inner tubes out. I know that you can do this with amps but it just doesnt really seem right to me. Does this sound like a good idea so that I can get some dirt on that amp? Or would it be just a better idea to try new tubes that saturate quicker?

Thanks ahead,
-Sam


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Post subject: Re: Pulling Tubes...
Posted: Tue Nov 20, 2007 2:13 pm
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Joined: Tue Nov 20, 2007 11:21 am
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MrGravity1337 wrote:
Hey everyone,
Im new to the forum but im a fan of Fender gear and all so its about time I start posting!

Anyways, I have a Fender Twin Reverb that I had recieved a few years ago installed with 4 JJ Tesla 6L6GC tubes. I heard from a friend that if I wanna crank that amp that its possible for me to pull 2 of the inner tubes out. I know that you can do this with amps but it just doesnt really seem right to me. Does this sound like a good idea so that I can get some dirt on that amp? Or would it be just a better idea to try new tubes that saturate quicker?

Thanks ahead,
-Sam


Yes, it will work, but with some considerations:

A/B class amps with 4 tubes are effectively 2 pairs of tubes wired in parallel to the output transformer. So, yes, you can pull either the inner or outer most pair of tubes, but this also changes the output impedance. You also have to change the impedance of the speakers to match, or else you risk damaging your output transformer and/or tubes and/or the rest of the amp. Removing 2 tubes effectively turns a 4 ohm amp into an 8 ohm amp, and running a 4 ohm load with 2 tubes removed will "overload" the output stage (think of it as doing 55 mph in car with a V8, as opposed to one with a 4 cylinder); the over all output volume will be similar, but the tubes are working twice as hard)...

At the least, you'll go thru the 2 remaining tubes much faster. At the worst, you'll get meltdown of a component (or several). I'd check with a tech before you do this.

Another option is a quality power soak such as a THD Hot Plate, Scholz Power Soak (if you can find em), the Marshall Power Brake or the Dr Z/Trainwreck version. Placed between the amp output and the speakers, it allows you to run the amp at full blast, then back off the volume using the power soak, which dissipates the unused energy as heat (its essentially a collection of large resistors which get hot and radiate energy like a heater).


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