[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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