N5AIT Allan Stephens
MODSTEPH at ACS.EKU.EDU
Wed Nov 3 19:07:54 EST 1999
You might recall the Lysco 600 with 450 volts on the key
from "repairs" and "modifications. Over the last few days I finally
got it figured out (decided that I was NOT just going to pass it
along, a deathtrap waiting to close on the unwary). Couple of
things included the discovery that there are two different RF wirings
for the Lysco 500/600 (and "S" models), and that the one I was
working with was the newer one - and I had the older schematic.
That taken care of helped a bit, and re-doing the critter a la
the newer schematic got it up and going - with about 70 volts on
the key (grid block keying - one of the "changes" had been replacing
the dropping resistor across the key with a disc capacitor -
effectively presenting an open circuit to ground at that point).
Few other corrections, one new filter cap set-up, and voila!
For a rig that first came out in 1950 it is an amazingly
stable one, and keying is chirpless (key all three stages,
oscillator, mult/buffer, final: two 6AG7's to an 807). All
bands 10 thru 160, good vfo (which can be used to "bend" xtals
when xtal control is selected), and with a little tweaking 30
watts out. Two controls (not counting ON-OFF and VFO-XTAL
switches): VFO and plate tuning. Simple, easy, works!
So another rig restored, frying danger from key much
reduced, and a good mental challenge!
73, Al N5AIT
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