[GreenKeys] Loop Supplies (was: any missing USB-tty adapter orders?)

[Jim Backus]

Hi

Comments on MJE340 noted. It certainly dates back to 1982 where it is 
shown in ARRL handbook RTTY section.

Unfortunately the availability of high voltage semiconductors has been 
affected by the demise of CRT TVs with their need for high power 
scanning circuits. A while ago I worked for a company that made solid 
state modulators for magnetrons and finding devices to switch high 
current, high voltage fast was a part of the challenge.

Regards

Jim

On 19/05/2016 01:50, Bob Camp wrote:
> Hi
>
> High voltage supply is whatever you happen to have. Something in the 80 to 100V range is plenty.
>
> Coils all go in series between B+ and the collector of the MJE340. Two neon bulbs in series go across the set of
> coils.
>
> Bias resistor goes from B+ to the MJE340’s base
> Zener goes from base to keying input hot side.
> Emitter of MJE 340 goes to keying input hot side to ground.
> Keying input cold side goes to the return on the B+ supply.
>
> In practice, I preferred to run a separate keying loop and drive the magnets with a MJE340. The keying loop ran
> at low voltage.
>
> There is no reason to stick with the 340 these days. It’s a ghastly old part by now. The approach was simple and it did work.
> I believe it came out of RTTY Journal.
>
> Bob
>
>
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