[AMRadio] Pw Supply

Brett gazdzinski brett.gazdzinski at verizonbusiness.com
Thu Dec 7 17:49:59 EST 2006

> Just looking at the spec's, Jack, for a single 813...  in Ham 
> service, 
> they say you can run 2500v on the plates, at 225mA, but in the same 
> chart, says the max is 450w max.  Sorry... the math just 
> don't add up.  

I think 2000 volts is max in plate modulated service.
As long as you do not exceed the plate dissipation, you
can run higher voltage or current, you could likely
run a pair at 2500 volts and 300 ma, or 2000 volts at400ma,
or 1750 volts at 450 or 500 ma.
More voltage usually works better though, as you have to
worry about cathode emission and current losses in things.
Almost everything I ever used did better at higher voltage
lighter current...

> But, if you use a single 813 in the final, and modulate it 
> with a pair 
> of 811's, you'll be at, or over the 'legal limit' anyway.

A single 813 at 2000 volts and 200ma will give about 300
watts out.  I don't usually get 4 times the carrier power
on the pep watt meter, more like 3 times, so that is only
900 to 1000 watts. Depends on your voice maybe...

A pair of 811A's wont do well enough to modulate 2 813's
at full bore. Its good to have at least as much audio
power as DC input to the RF deck, its clean that way.

> Either way, 1500w PEP is the Maximum Power Output we're 
> allowed to run 
> these days.  Not like in the old days, when 1kW DC input, measured at 
> the plate of the output tube(s) was the law (and a helluvalot 
> easier to 
> measure)

With a pep reading watt meter, you don't even have to do
any math. The meters read all over the place 
with a little swr though...and who knows about the calibration...


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