[AMRadio] AM Usage with Linear AMPS


Brian Carling bcarling at cfl.rr.com
Mon Nov 22 20:43:41 EST 2004


On 22 Nov 2004 at 20:23, W7QHO at aol.com wrote:
 
> Going to shorten it's life considerably. 

Theoretically maybe. Have you tried it. How can you know 
for sure? Theory says a bumble bee can't fly. My 811A tubes 
never burned up.

Where did you get your 30% number from? Who transmits 
their AM with carrier only!? I can't see how a 50 watt carrier input
will cause an 811A to DISSIPATE 100 watts!
Where are you getting the additional 50?

> To properly adjust a linear amp for AM it is necessary to tune the thing up for the peak power 
> level, i.e., 200 watts for a 50W carrier. The linear will be about 60% efficient at this output level. 
> Then WITHOUT CHANGING THE TUNING adjust the output from the AM exciter to provide for 
> 50W out of the linear with no modulation. The problem here is that the linear will now only be 
> running about 30% efficiency under carrier-only conditions and the 811 would be dissipating 
> something like 100+ watts. The 811A, of course, is only rated at 65 watts.
> 
> Dennis D. W7QHO
> Glendale, CA





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