[ARC5] Modulation for ARC-5 transmitters.

[J Mcvey]

Well that wouldn't work in MY key jack, because I use the original SCR274 relay scheme.However for those who are using the cathode keying mod, you might want to consider that circuit using modern semiconductors with a mosfet cathode driver. 
It could be built inside the transmitter!

 


     On Thursday, October 8, 2015 7:58 PM, Kenneth G. Gordon <kgordon2006 at frontier.com> wrote:
   

 Leslie:

There was an article some time ago in Electric Radio Magazine on 
controlled-carrier AM modulation which I found to be a very well-done article, 
and it explained a lot.

There was also a recent article in ER on the same subject, but I was very 
"under-whelmed" by that article. I found it very difficult to follow.

My first transmitter, a Heathkit DX-35 used CC modulation, and I have 
always liked that mode ever since.

You might also consider this modulator:

http://www.w7ekb.com/glowbugs/projects/SimplestModulator.pdf

Which plugs into the key-jack of any cathode-keyed transmitter. I tried one of 
these once and was very pleasantly surprised at how well it worked and how 
good it sounded.

Here is another article on that same modulator with different info:

http://www.w7ekb.com/glowbugs/projects/SimpleGridModulator.pdf

Using CC modulation, you should be able to achieve output equal to the full 
plate dissipation capability of your final amp tubes, which in the case of a 
pair of 1625s, should be close to 60 watts. (807/1625 has 30 watts PD rating 
in ICAS)

Also, CC modulation works extremely well when fed into a modern linear 
amplifier, unlike straight plate modulation, which must be "dialed back" 
severely to prevent the following linear from being overloaded.

Ken W7EKB
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