Steve

Yes, I agree ... your calculations represent what would be possible with a very efficient (80%) Class C rf amplifier, and an efficient modulator... biased for very low resting current.

You are an acknowledged grand master at designing and building very efficient transmitters

In my Ranger, the RF output (at carrier) is about 40 watts with the B+ set at 550 volts and about 125 mA of plate current (ignoring the screen power to keep things simple). So the efficiency of the rf amplifier is around 40 Watts / [550 volts x 0.125 amps] = 40 watts / 68 watts ~ 58%

. I'm sure that I could tweak the Ranger to do somewhat better... but nowhere near 80%.

My KW-1 produces 420 watts output at carrier with 2100 volts B+ and 320 mA of plate current. So the efficiency of the KW-1 is 420 watts / [2100 volts x .320 amps] = 420 watts/672 watts ~ 62.5%

[When Bob Sullivan tested it with the normal plate voltage of 2500 volts and the normal plate current of 400 mA, he measured 1000 watts in and 600 watts out => 60% efficiency]

With respect to the modulator, a stock Ranger modulator runs at 50 mA of resting current with 550 volts on the plates of the modulator tubes. That's 27.5 watts of resting modulator power (as you point out, not including the filaments).

So the overall efficiency of a stock Ranger, at carrier, is: 40 watts /[68 watts + 27.5 watts] = 40 watts / 95.5 watts ~ 41%

If you upgrade the Ranger to 6550's, then the resting current of the modulator is around 100 mA, and the efficiency drops to 40 watts / [68 watts + 55 watts] ~ 32.5%

The modulator of the KW-1 draws 50 mA of resting current (only considering the 810 modulator output tubes) at 2100 volts. So the resting power of the modulator is 105 watts. The overall efficiency of the KW-1 at carrier is 420 watts / [672 watts + 105 watts] ~ 54%

As you point out, when you add in everything else... the electrical power consumption of a stock KW-1, in AM mode, with no modulation is specified in the manual as 2280 watts. The corresponding stock KW-1 carrier output power is 600 watts. So the wall plug efficiency at carrier is 26%.

For comparison, the wall-plug efficiency of my Class E transmitter + Class H modulator, at carrier = 50% [i.e., 400 watts of electrical power in, and 200 watts of rf power out]

Best regards

Stu