Halving the power of a tube amp

[boedonaldson]

ok heres the senario. Say ive got a tube amp thats 100watts and i want it to be 50watts.
-Do i remove the two outer output tube, and is it as easy as just pulling them out?
-In doing this will it have any effect on the sound or workings of the amp if i crank it near full with this done?
-How could i incorporate a 1/2 power switch into the amp so that i could just bypass two tube out of the output?
-Could i do the same thing with a 50watter for 25watts,if so how?
Im am baseing my research around the Marshall JCM800 series amplifiers (single channel/high lowe inputs)
Any input on this topic would b helpful, thanks.

[bancika]

post your question on www.ax84.com/bbs, it's more likely that someone will know. I think there's similar thread going on right now.
one more thing, halving power will not make it 50% less loud. Difference is much smaller. You'll need drastic power reduction to get significantly lower volume

[petemoore]

  Potentially Lethal Voltges Dwell inside your tube amp, even after it's turned off and unplugged.

[R.G.]

One thing most people here don't notice is that GEO has a lot of information on tube amps as well as effects.

It's worth your time to go read the Tube Amp FAQ, which addresses this issue directly.

You *can* lower your amp's power by pulling two of four output tubes. You have to pull the correct two tubes to do this.

It will not be the same amp, just half power, as the output transformer does not change and the power supply does not change, and these are still sufficient for the full power.

You could put in a switch that deactivated two of your output tubes by turning off the heater current to them. This may or may not be a good idea.

You could do the same thing for a 50 watter - if it used four tubes. Most 50 watters don't.

The most effective way to lower power is to lower plate voltage. Unfortunately, this is much more complicated than removing tubes.

Half power is NOT half loudness. The human ear hears loudness logarithmically. Something half as loud is about 1/10 the power. Something half the power is just perceptibly quieter.

Most of this is in the Tube Amp FAQ; so is a lot more that you'd really like to know.

[Ed G.]

What about a pentode/triode switch?

[boedonaldson]

so how would i wire up one of them?

[brett]

Hi.
Have a read of the stuff at RG's site.

This quote is very relevant: "The most effective way to lower power is to lower plate voltage.
Unfortunately, this is much more complicated than removing tubes."

You can check out some schematics of amps that have low power switches.  A good example is the 16W/65W switch on the MusicMan and Fender amps with 2 x EL34s and switchable plate voltages.  You can find the Musicman schematics on-line at the Ernie Ball site.  (NB Halving the plate voltage reduces power to 1/4, all other things being equal)

Keep the pre-amp tubes running at their favourite voltage.  Chances are high that they will get weird and/or dirtier if their plate voltage drops.

cheers

[Aharon]

Other options are:

Power attenuator.
Yellow Jacket adapter.
Turn down and use an effect box to get distortion.
Hope it helps
Aharon