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A passive attenuator in the effects loop may be an option. Something similar to this:

http://www.ebay.com/itm/Omnisonic-Tube-Amp-VOLUME-BOX-for-PEAVEY-Delta-Blues-Valveking-Classic-30-50-/140977980384?pt=LH_DefaultDomain_0&hash=item20d2f143e0

For the volume jump issues (if I read that right), you can try out different tubes in the preamp stage (such as replacing a 12AX7 with a 12AY7) and replace the volume pot with an audio taper pot so you don't have that volume setting at 1 to low/ setting at 3 blows the windows out and yet still retain the sound you like. Some also play with different speakers as well. That may get you in over your head and more involved than you'd feel comfortable with and gets you into an area where many books have been written on the subject.

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amazingly enough not one person here mention ppimv since the valve king is basically a marshall clone. perhaps you should check that out

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  • 1 month later...

I think I read once that you can just yank one of the push-pull pairs of tubes out of the circuit and cut your power in half that way. I'm not sure if that would play well with impedance matching though. Since the power tubes are in parallel, you'd be doubling the plate impedance (I think?) by taking out a pair, so you'd just need to switch your speakers to the tap for 1/2 their impedance.

This might be totally wrong. Anyone know the right answer?

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One, raising the resistance on a speaker for a tube amp load will FRY your amplifier (if we're talking enough to reduce volume considerably).

Two, the only real safe ways to do what the OP is asking is with a variac (fancy version of an attenuator that vankirk mentioned), or with a yellowjacket to lower output of your power tubes.

http://www.tubesandmore.com/tech_corner/yellow_jacket_tube_converter_technical_information

Too many variacs to list, you can research on google.

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Careful with that axe, Eugene.

Removing one tube in a pair *may* work, but the results can be unpredictable. Even assuming you can get a 50% reduction in power, a 50W amp running at 25W output power in a small room is still going to be ear-shatteringly loud. It's not just a simple case of reduced power either - bias changes, tone changes, reduced load on the power supply may mean that components are run above their voltage ratings...the short answer is "it depends".

A variac should most definietly NOT be confused with an attenuator. A variac is a variable transformer used to raise or lower the AC mains supply coming out of the wall. An attenuator is a device used to reduce a signal output down by a certain amount. The former is (allegedly) what Eddie Van Halen used to create his Brown Sound by changing the voltage his Marshall ran at. The latter is what you'd stick in between the amp and speaker to bring the volume down to a more managable level. Despite what EVH may have done with his variac, you should never run a tube amp flat out at reduced mains volts for any length of time. Premature failure of the tubes is likely.

Whichever way you look at it any attenuation method will introduce tonal foibles of their own. Reducing the master volume, installing an attenuator on the speaker or in the FX loop, modifying you amps' circuit topology to use a more elaborate volume control or whatever will all change the sound of the amp. Trying to micro-size a 100W Marshall down to an iPod will always be a trade-off in some way or other.

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And curtisa delivers the warning I was looking for. Pulling power tubes is probably not the best idea.

If you're having trouble adjusting the master volume to exactly the level you want, you could always swap the knob (not the pot, just the knob) out for one with a larger diameter. You'll be able to adjust the master volume more precisely that way (more linear motion per rotational motion). I've got a huge master volume knob on an old 50W hight-gain head and it works pretty well.

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Running a tube amp off of a variac and turning down the voltage is NOT a good idea at all!

While you are reducing the voltage on the amplifier tubes which will indeed give you lower output power you are also reducing the voltage on the tube heater supply which is usually designed to run at nominally 6.3 volts or 12.6 volts +/- 10 % depending on how the heater supply is configured. Reducing the heater supply below its lower limit will reduce your tubes life and accidentally increasing it above the upper limit will most definitely destroy the heater coil.

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On re-reading my earlier comment regarding using a variac, I think I need to clarify a little:

"Despite what EVH may have done with his variac, you should never run a tube amp flat out at reduced mains volts for any length of time in an effort to reduce volume to apartment levels. Premature failure of the tubes is likely." (emphasis mine).

Using a variac to lower the mains voltage by no more than 10-15% from nominal is actually perfectly acceptable, and is exactly what Mesa do with their "Tweed/Spongy" switch on a few of their amp models. Flicking this switch reduces all voltages in the amp by the same percentage and is technically no different than running your amp from a variac and winding it down by a small amount. However the volume drop is inconsequential and will still result in a nasty phone call from the neighbours or cops - the variac in this case is acting more on the tone of the amp than the volume.

Depending on where you live you may find that reducing the mains voltage by a small amount is actually a good thing. You may have an old vintage amp of some kind that was originally designed to operate on 110VAC from the wall, and your local supply is closer to 120V. Reducing the mains voltage to its original spec will have a positive effect on tube life and other voltage-sensitive components in the amp.

The real danger is just winding down the variac willy-nilly without paying attention to what effect it has on the amp as a whole. Reducing the mains voltage also reduces the filament voltage. Reduced filament voltage also reduces emission in the tube, which in conjunction with lots of plate current for long periods of time results in cathode stripping of power tubes (which I will admit is probably not going to cause the end of the world, but does mean you'll have to replace your power tubes more frequently).

As Keith mentioned above, raising the variac above nominal is most definitely asking for trouble. Any device that has such an drastic effect on the operation of an amp should be treated with caution - it's easy to accidentally set it to a wrong value and not realise until the smoke comes out.

In short, I guess unless you know exactly what you're doing with a variac it's probably best you find a different way to tame that Plexi.

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have you ever cranked up the voltage on a marshall to about 140? very nice, indeed but again like you say its not sustainable as it will strip of the filaments coating. however you can wire it up to do the same thing, i built a clone like this years ago and its one of my favorite tones. still a ppimv is easy install easy to reverse and won't kill your amp. is it exactly the same as a cranked up amp.. no but its one of the most popular mods done to that style amp.

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