[AMRadio] AM Usage with Linear AMPS

John Coleman, ARS WA5BXO wa5bxo at pctechref.com
Mon Nov 22 23:11:49 EST 2004

My experience (which is very little when it come to these sweep tube
rigs) is they or rated for a belch or some thing short and don't hold up
to a fix channel field day adventure with out tube replacement.  I had a
DuaoBander mobile for a while rated a 400 watts PEP input I never saw
more than 150 watts output while whistling in the mike.  It was in
perfect condition and would light a 50 watt bulb with normal speech.  I
thought it would have blown it out.  I was very disappointed. Yet, it
was one of the most heard radios all over the country by many AMers in
the late 80s.

John, WA5BXO

-----Original Message-----
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net] On Behalf Of Brian Carling
Sent: Monday, November 22, 2004 9:55 PM
To: Discussion of AM Radio
Subject: RE: [AMRadio] AM Usage with Linear AMPS

Aren't there a lot of commercially built amateur radio linear 
amplifiers and RF finals that exceeded he manufacturers MAX 
Pdiss rathings over the years, by adding a COOLING FAN to take 
away the extra heat?

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.

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?

How about some of the othre rigs that rated their 2 sweep tube 
finals for 560 Watts or even 800 watts!?

Then youhave peak Pdisses of 140 to 200 watts between the two 
sweep tubes, most of which are rated for no more than 40 watts.

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