Bit - really HARD!

[Perry Ballinger]

Al:

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
insulators are!)

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....

73,

Perry    w8au




At 04:10 PM 10/20/99 -0400, you wrote:
>Gang:
>
>     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  The entire string had been replaced by a single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
>
>