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Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by atomheartmother, Dec 3, 2004.
Good suggestion! Might have to raise treble et tings to compensate.
A preamp tube change does absolutely nothing to alter the power output of your amplifier. The output tubes, power transformer and output transformer are the items controlling your amp's power output.
Personally, I'd never take the Yellowjacket route for lowering an amp's power output, but maybe I haven't given them a fair shake. I'd offer that if you really need less output power, either use an attenuator or get a smaller amp.
Because the people talking don't know how their amp works, and they might use the same words to mean different things.
Your amp's output section is capable of some amount of clean output power, and it requires some amount of drive voltage to make all of that output power. Your preamp section, along with shaping your guitar's sound, is there to boost the signal from your pickups to the level that can drive the output section. There is a certain amount of amplification (that engineers call "voltage gain" though they don't necessarily mean "distortion") given by the preamp to get from "pickup level" to "output section driving level".
Swapping in lower-gain preamp tubes just means the preamp doesn't boost the signal as much as it did with the stock tubes. If you leave your volume control at the same numerical setting, the amp is "quieter". Nevermind your 50w output section will still output 50w if you turn the volume control higher so the output section receives the same driving voltage it got with the higher gain tube. And now that the preamp is driving the output section with less voltage for the same volume control setting & the same guitar input signal, perhaps the output section is distorting less and the player perceives they've gotten "more headroom".
Really, these people are kidding themselves. The signal levels at which different parts of the amp distort usually haven't changed, and the total clean volume the amp is capable of hasn't changed. Power output hasn't changed either, though there may be a "volume reduction" if the player keeps the controls at all the same settings after installing the lower gain tube, but they could have achieved the same simply by turning down the amp's volume control.
There is a small caveat/exception to the above that some lower-gain tubes can accept a larger input signal before distorting. If the player installed such a tube late in the preamp circuit, they might indeed be getting a small bump in "headroom" but it's difficult to speak generally about that since it's circuit- and situation-dependent.