[ARC5] Fun with the AN/GRC-109

[Kenneth G. Gordon]

On 8 Aug 2013 at 19:41, Robert  Eleazer wrote:

> Is that the modulator that consists of some ganged together
> transistors, sort of Darlington style and you plug it into the CW key
> jack and plug a mike into it?

Well, it works on somewhat the same principal. I think you are talking about 
Cunningham's modulator. 

I have a schematic for that too, but no, this one uses tubes. Mac mentioned 
the correct one: it uses 6Y6s as the modulator tube or tubes.

It gets its plate voltage from the cathode of the tube it is connected to. 
Plugging it in, reduces the plate voltage by the same amount that the 
modulator "needs", usually 1/2 of the available voltage.

When you plug it into the key jack, the plate current drops to 1/2 its CW 
value.

I used one of those with my DX-35 back in the 1960s. Although it modulated 
every tube in the transmitter which had its cathode connected to the 
key-jack, I never experienced any FM with it.

Here is a URL to the entire article:

http://www.w7ekb.com/glowbugs/projects/index.html

Scroll down on that page to just above "Crystal Control" and you will find two 
PDF articles with different titles that describe the exact same modulator.

There is a link on the web somewhere for a 250TH transmitter built by 
Dennis Brady with help from Patrick Jankowiak.with a cathode modulator 
which works extremely well.

Here are two links to their work:

http://www.montagar.com/~patj/cathmod01.htm

and

http://rawfire.torche.com/~opcom/dbrady1/index.html

Ken W7EKB