Aaack! I messed up the DX-100 audio!

[Jordan Arndt]

P.S... the increase capacitance could be loading down the ckt to where oscillation
is erratic or not 'clean'.... 73 de Jordan...

Jordan Arndt wrote:

> I would think the lower B+ from the OB2 would also decrease the drive available
> out of the tube...it could also increase 'chirp' from the VFO...not having the
> schematic handy, I can't say what the effect of the 47pf to 62 pf change might
> be, except to couple more of the signal to whereever the cap is going....73 de
> Jordan...
>
> Brian Wood wrote:
>
> > 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
> >
> > -----------------------------------------------------------
> > This list is a public service of the City of Tempe, Arizona
> > -----------------------------------------------------------
> >
> > Subscription control - http://www.tempe.gov/lists/control.asp?list=HEATH
> > To post - HEATH at LISTSERV.TEMPE.GOV
> > Archives - http://interactive.tempe.gov/archives/HEATH.html

-----------------------------------------------------------
This list is a public service of the City of Tempe, Arizona
-----------------------------------------------------------

Subscription control - http://www.tempe.gov/lists/control.asp?list=HEATH
To post - HEATH at LISTSERV.TEMPE.GOV
Archives - http://interactive.tempe.gov/archives/HEATH.html