[AMRadio] AM Transmitter Advice??


W1EOF w1eof at hamnutz.com
Mon Jan 30 17:35:46 EST 2006


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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