Valves,Tubes.......

[Mark]

Paul, sorry for the delayed reply, I've been on holiday for the last week. I'm glad the information was useful.

With regards to your removing the valves question: As a "get me through the gig" solution running with two valves as you suggest is ok, but I wouldn't suggest this as a long term solution to reducing the power for two reasons.
Firstly; if you are using your Twin for steel guitar you want as much head-room as possible, you're carrying around the weight of a Twin, so why not use it at its optimum capability? If it's too loud, turn down the volume.
Secondly; you have a power supply capable of driving a 4 x 6L6GC output stage; with only two power valves fitted the 6.3V heater supply will be under-loaded and this will cause the heater volts on all valves in the amplifier to be increased above the nominal value, this increases the valve temperatures and greatly reduces the valve life; in addition the biasing will need adjusting to suit the new conditions, many Twin's rely on a preset bias system that will almost certainly not operate correctly with just two power valves fitted; and the two power valves will be feeding an output transformer with primary winding impedances designed to be driven by a 4 x 6L6GC push-pull stage, by using two valves the transformer will be under driven or present peak currents to individual power valves higher than normally seen, both situations are not good news.

I guess the bottom line is, it's not a good idea to run your amp like this. Buy an amp that has a 2 x 6L6GC output stage if you need less power... it will lighter too!

The other thing to keep in mind here is output power and volume is not a linear function, it's a logarithmic function. i.e. if you have a 10W amp and want to double your volume you need a 100W amp; I should say here, this is only a rough guide, many other things come into the equation; but from this you should deduce that cutting your output power in half will only slightly reduce your volume.