[AMRadio] AM Usage with Linear AMPS


W7QHO at aol.com W7QHO at aol.com
Mon Nov 22 23:40:01 EST 2004


In a message dated 11/22/04 7:56:07 PM, bcarling at cfl.rr.com writes:


> One thinks of MANY sweep tubes rated for so-called Pdiss of 16
> watts and 20 watts that are regularly run at hundreds of watts of
> RF! The tubes don't seem to melt.
> 
> I think of the ubiquitous 6JS6C with a rating of 30 watts.
> Yaesu ran a pair of these at 260 watts input in their FT101 series.
> Many guys ran them at 260 watts p.e.p. on SSB and 260 watts CW.
> Assuming 65% efficiency, you have 35% of 260 watts going into
> the plates. That is to say 91 watts split between the two tubes.
> UH oh - POP! But no, they didn't.
> 
Yaesu's instructions were "don't hold key down for more than 10 sec on tune 
up!"   Otherwise - POP!   Voice is a low duty cycle signal.   In SSB service 
the average dissipation level can be kept within reasonable limits unless heavy 
voice processing is involved.

> 
> Then when you throttle that FT-101 back to 40 watts input on AM
> and go to your 30% efficiency (if it is) then you are actually
> putting only 20 watts carrier per tube which is SAFER.
> 
> Is that correct?
> 
> 
Actually, on AM the FT-101 is throttled back to something like 100 W INPUT, 
25 - 30 W carrier OUTPUT.   Optional fan recommended.

> How about some of the othre rigs that rated their 2 sweep tube
> finals for 560 Watts or even 800 watts!?
> 
Yes, the SWAN 750 for example.   Had one in our Club back East.   Be light on 
the key with this sucker or definitely POP!
 

Dennis D. W7QHO
Glendale, CA



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