Beware of buying a higher power amplifier and running it at a lower power. As the output power is lowered, the efficiency drops, so a higher power amplifier can actually dissipate as much power in the output devices at less power as when running full power.
Here is the efficiency curve of the Icom 2KL amplifier compared to a class A and class B theoretical amplifier. There are some amplifiers that change the power supply voltage to a lower voltage when running lower power to keep the efficiency up.
You are right - efficiency is lower, but output power is lower too. Thus dissipation will ultimately be lower, but not in linear proportion to the reduction of the output power.
Eff is everything in any amp, SS or tube. My yaesu FT-1000MK-V is 50 % eff when run at 200w pep out..which drops to just 35%, when run at 1/2 power, or 100w pep out. Diss is a tiny bit lower when running 100w pep.
On a side note, the SS amp made in the UK also has 3 x different Vdc's used, depending on PO. ( it uses a pair of 188's). Same deal, lower vdc's used, when using lower PO. Then eff stays high at all times. The german B26 amp only has one vdc. The SPE has 3.... for 500/1000/1500.
On my HB tube amps, to keep eff high, when reduced PO required, I can lower the B+ (Model 88, single pole switch, to change taps on the sec of the dahl plate xfmr). 6 x taps to pick from. (also 6 x taps on the primary). Then by tweaking the drive for correct plate current, plate load Z remains the same, and eff stays the same.
It's too bad they didn't provide for at least one lower vdc on the LUX. The eff on the LUX with just 500w PO will be way down. Ditto with 750w PO, but not quite as bad.
