Aaack! I messed up the DX-100 audio!

[Brian Wood]

Having now spent several days working on some more mods for the DX-100 and
then curing the "grid current flicker" (turned out to be the 47 pf mica cap
on the grids, suggested by Bob W3CD), I fired the rig back up and everything
looked just fine until I tried to talk. Hoo-boy did it sound distorted.
Sounded less so when the finals weren't putting out 60W (lower than the
80-90W I got before on 10M - damaged tubes?). RF feedback? Here's all I did
this time:

1. Moved the 6AU6 plate to point L and changed the tube from a 0A2 to a 0B2.
(Reduces drift)

2. Removed the drive pot and associated resistors and put in a drive pot mod
suggested by Ed, AA8TV consisting of a HV transistor, 1M linear pot and 470K
resistor. It's much smoother now, and works well.

3. Cleaned the final tuning cap and put some white lithium grease on the
rear bearing to make it turn easier.

4. Re-soldered the neutralizing wire on the driver tuning cap. Tried various
positions to see if neutralization is off. Very hard to tell any difference.

5. Put a new, non-shorting meter switch in place of the old one.

6. Repaired the RF choke going to the plate of the 5763. I still measure
500V on the non-RF side of it, which is pretty odd. Must be RF getting in
there, so that could be the problem, but why now and not before? Tried a
.0033uF bypass disk there to no avail.

7. Replaced the 47 pf mica cap with a dipped silver mica 62 pf cap (all I
could get my hands on in that ballpark; first tried 220 pf and got no drive
at all!)

Sigh. Any advice?

73,

Brian

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