[AMRadio] AM Transmitter Advice??

John E. Coleman (ARS WA5BXO) wa5bxo2005 at pctechref.com
Tue Jan 31 10:36:20 EST 2006

Mark is correct:

A pair of 813s linear on AM is at best a little better that the Johnson rig
with three 6146s class C plate modulated.  This is assuming that you will
not run the 813s beyond the CCS plate dissipation limits (100 watts per
tube).  If your solid state rig is 100 watts PEP (equivalent carrier about
20 watts) then this will be a big improvement.  If your driver rig is 100
watts carrier and 400 to 500 watts PEP then you will not see a lot of
difference when you go to the 813s linear.

How ever 813s class C plate modulated will run the legal limit easy.

John, WA5BXO   

-----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 4:36 PM
To: Discussion of AM Radio
Subject: RE: [AMRadio] AM Transmitter Advice??


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?.


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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