I wonder just what a pair of 813s are actually capable of in ICAS service with forced air cooling? We should be able to run elevated plate voltage (if we can keep them neutralized on the higher bands) and increased plate current beyond the old standard specs.
Anybody want to make an educated guess as to how much power we might reasonably expect from a pair running CW class AB1 under those conditions?
In summary, I guess 1254W @ 4KV in AB1, and 1200W in class C, both with a 25% duty cycle.
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If you consider the plate modulated class C information, then:
pair -
icas table
300W @ 2000V/200mA - carrier
1200W @ 4000V/400mA - 100% modulation
Pd=200W per tube
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ccs table
180W @ 1600V/150mA - carrier
720W @ 3200V/300mA - 100% modulation
Pd=120W per tube
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The above is just from the TT-4 book, but the voltage and current are not exagerated, they are the conditions that would exist at the peak of the modulation cycle.
A CBer I knew in the 1980's claimed to make a 1KW carrier with four of them and 4500V as a linear amp, but consider the source and I never saw the amplifier. I imagine he did not engage in rag chews with that.
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Taking the AB1 data and extrapolating to 4000V, which is allowed in class C as a peak voltage:
--pair @ peak conditions - or if CW, then key down:
490W @ 2500V/290mA - AB1 peak output by the book
Pd=117.5W per tube
G2 input=20.25W per tube
at 4KV -
1254W @ 4000V/464mA - same load impedance 4750 Ohms per tube (Rl=2375 Ohms), and other voltages but extrapolated to 4KV plate
Pd=301W per tube ?
G2 input per tube - I don't know how to estimate it but I think it decreases as Eb increases. rating is 22W. Will it be a factor?
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Why run AB1 for CW? 200W dissipation per tube in class C vs 300W in AB1.
Can CW be described as about a 50% duty for 30 seconds, then off for 30 seconds?
That would be an integrated duty cycle of 25%.
If so, then with this 25% duty, 4X the dissipation might be ok, depending on whether the plates melt before the end of each 30 second transmission.