[AMRadio] AM Transmitter Advice??


Gary Schafer garyschafer at comcast.net
Mon Jan 30 17:46:19 EST 2006


He is telling you that a pair of 813's as a linear are good for only 125
watts of carrier output on AM and that it takes tubes with at least 800
watts plate dissipation to run the legal limit on AM linear.

73
Gary  K4FMX

73
Gary  K4FMX

> -----Original Message-----
> From: amradio-bounces at mailman.qth.net [mailto:amradio-
> bounces at mailman.qth.net] On Behalf Of W1EOF
> Sent: Monday, January 30, 2006 5:36 PM
> To: Discussion of AM Radio
> Subject: RE: [AMRadio] AM Transmitter Advice??
> 
> Dennis,
> 
> I was with you until the end where you say: "Bottom line -- If you're
> going
> to build a linear do it right and go for a pair of 4-400's, single 4-
> 1000A,
> 3-1000Z or one of the big Russian tubes I've seen on eBay recently."
> 
> Assuming one is going to build a linear, and so putting aside other issues
> such as linear vs plate modulation, why do you think it makes a difference
> what tube is used? Are you referring to running a linear at greater than
> legal limit?.
> 
> 73,
> 
> Mark W1EOF
> 
> 
> 
> > -----Original Message-----
> > From: W7QHO at aol.com [mailto:W7QHO at aol.com]
> > Sent: Monday, January 30, 2006 5:01 PM
> > To: kq4by at rocketmail.com
> > Cc: amradio at mailman.qth.net
> > Subject: Re: [AMRadio] AM Transmitter Advice??
> >
> >
> > Linears for AM -- here we go again for at least the third time in
> > the past 12
> > months.
> >
> > Basic considerations:
> >
> > 1.   Under carrier only conditions a correctly designed and
> > adjusted linear
> > amplifier will be operating at about 33% efficiency.   So, with a
> > pair of 813's
> > the math works out to 125 watts of carrier, obviously not worth
> > the effort if
> > you're starting off with a 100 W carrier exciter.
> >
> > 2.   The linear must be initially tuned up at the peak RF output
> > value which,
> > in turn, requires that the exciter (or some other source) must be
> > capable of
> > providing the input necessary to do this.   Typically, his would
> > be 4 times
> > the carrier value but expect to hear a lot more on this from the
> > "asymmetrical
> > speech waveform" crowd.
> >
> > 3.   "Real AM" can only come from a plate modulated class C PA in
> > the view of
> > certain members of this community.   At the same time, big mod iron is
> > expensive and hard to find.   Also, for a legal max rig the wall
> > plug efficiency of
> > "high level" and "linear" is not that much different in the final
> > analysis.
> >
> > Bottom line -- If you're going to build a linear do it right and go for
> a
> > pair of 4-400's, single 4-1000A, 3-1000Z or one of the big
> > Russian tubes I've
> > seen on eBay recently.   I use my HB 3-1000Z amp on both SSB and
> > AM, BTW.   Works
> > FB.
> >
> > Good luck with the project.
> >
> > Dennis D. W7QHO
> > Glendale, CA
> --
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