Removing Power Tubes

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spoonman
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Posts: 22
Joined: Sat Jan 25, 2003 4:48 pm
Location: Canada

Post by spoonman » Fri Apr 04, 2003 1:24 am

I used to run my Graphic 120 head with two of the power
tubes removed (and impedence in half). I inquired about
this a while back on this forum and was told to put them
back, because it would sound better. But when I returned
to the studio last week, everyone agreed that the amp
didn't sound as good as the last session. I took the tubes
back out and the great tone was back (especially in
conjunction with a Boss DS-1 Distortion). It was subtle,
but the tone was more transparent and more musical. The
question is, am I doing any damage to the head with the
tubes removed? It definitely runs cooler. Thanks for any
help.

saf_1
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Posts: 7
Joined: Wed Apr 09, 2003 7:01 am
Location: USA

Post by saf_1 » Fri Apr 11, 2003 3:33 am

Ok - I'm gonna kind of go out on a limb here, and answer this. I've heard this question addressed SOMEWHERE before, by Gerald Weber of Kendrick amps, or Andy Marshall of THD, or somebody like that - and I can't remember the exact answer but I think it goes something like this: in GENERAL when you have an amp using 4 octal (8 pin) power tubes (EL34's, 6L6's, KT66's, et al), in a class A/B configuration (in other words, not class A), that is making in the neighborhood of around 100 watts rms (your Graphic 120 falls into all these categories, BTW), then you can usually remove TWO of the power tubes without damaging the output section of the amplifier. This will cut your power in half (to around 50 watts), and subtly change the tonal characteristics of the amp. It will also allow you to crank the amp to get power tube distortion at a lower volume. The ONE caveat to remember, is that in a class A/B circuit (also known as "push/pull") the power tubes work in pairs, so if you remove two tubes, always remove either the outside two or the inside two - never both tubes on one side... in order to avoid damaging one of the transformers and/or some other component in the power section. Hope this helps answer your question.

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