Bit - really HARD!
w8au at SSSNET.COM
Wed Oct 20 22:58:30 EDT 1999
Interesting problem you had there. (And you thought you were playing it
safe by not putting your hand behind the rig where the B+ feedthru
Having had a few Lyscos over the years, and still having one, I am
surprised someone would do such a bonehead modification! Years ago, I
learned something from Lysco....how to make a "grid-blocked" keying
arrangement with NO grid bias supplies! Just float the operating ground a
few volts above chassis ground, enough to make the 807 cathode that much
positive with respect to the grid so you get "cut-off." The simplicity was
fascinating! Just tie the key jack across the last resistor in the bleeder
circuit string to short out the "bias" voltage and it keys.... How neat!
I then learned to tailor that last resistor to get a few mills static plate
current, to ease the "turn-on" of the 807. My, such neat memories!
Think you will eliminate a sure key click when you get your's back to
normal. Hope to hear it sometime....
At 04:10 PM 10/20/99 -0400, you wrote:
> Two nights ago I put the Lysco 600 on the air. Was doing
>fine with it... but in the course of things the back of my hand
>came across the key terminals and I got bit - HARD! Over the
>years I have got zapped, of course, but this really hit me.
> Next day, as soon as I finished repairing my VOM, I checked
>the voltage across the key -- about 450 volts... Certainly enough
>to kill the unwary/unknowing. I remembered what I had encountered
>when inside the Lysco a few days earlier: there was a resistor
>string that went to the key jack, with a final 1250 ohm resistor
>across the jack. The entire string had been replaced by a single
>resistor - across the jack - correct TOTAL resistance so the rig
>operated OK, but that put the full voltage on the key.
> So it looks like I WILL go back in and restore it to its
>original configuration, just as a safety feature if nothing else.
>I had noted what had been done in the change, but had not thought
>through it... At least I am still around to learn from this one.
> 73, Al N5AIT
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