[AMRadio] AM Transmitter Advice??

Brett gazdzinski brett.gazdzinski at verizonbusiness.com
Mon Jan 30 16:11:09 EST 2006

A pair of 813's at 2000 volts and 400 ma will give you 600 to
700 watts of carrier output, and will be running easy.

You would need a 400 watt modulator or better, I use a pair
of 4x150a tubes in ab1, good for 600 watts of audio at 2000 volts.
If you want single band operation, all you need to do is wind a tank
coil out of copper tubing.

For a simple, well working cheap and easy transmitter, its hard to beat
a pair of 812a's modulated by a pair of 811a's.
At 1500 volts, you get 300 watts out.
Triodes can modulate nicely, no screens to worry about modulating.
The 811/812 tubes are cheap, and in push pull link output, are stable
and easy to do. I use the kilowatt plug in coils, so I can change
bands if I want to.

Easy way is to build a class C rf deck and excite it with a rice box,
build a modulator and drive it with an 8 ohm output.
20 watts of audio will drive most modulator tube grids more then enough.

I never liked the amp route, loads of power input and big tubes
running hot, for little AM power output, and every amp adds distortion.

Amps are great for ssb, but add a carrier and they are not so great.



> -----Original Message-----
> From: amradio-bounces at mailman.qth.net 
> [mailto:amradio-bounces at mailman.qth.net] On Behalf Of Larry Keith
> Sent: Monday, January 30, 2006 3:07 PM
> To: Discussion of AM Radio
> Subject: [AMRadio] AM Transmitter Advice??
> Well, Let's see if we can change the subject.. 8-)
> I am gathering ideas for a homebrew AM transmitter..
> My friend, KR1S (Jim Kearman) is designing an AM
> transceiver, for me.  We plan for this to be a
> solid-state unit that will deliver about 100 watts
> out. It will be single band (75 meters) and I have
> been considering using that to feed a homebrew linear.
> I have the makings of a 2 x 813 amp thanks to my and
> Jim's hamfesting efforts.
> So far, we have been reading and kicking around ideas.
>  It seems that with the derating of the amp to handle
> the continuous carrier, etc.. may be more trouble than
> it is worth.  
> So, I would be interested in opinions as to the
> relative merits of using a linear vs high-level
> modulation.  And, pointers to existing circuits would
> be helpful..
> Any ideas?
> 73,
> Larry
> Larry Keith 
> 231 Shenandoah Trail 
> Warner Robins, GA 31088-6289 
> kq4by at rocketmail.com 
> 478-329-0030 (home)
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