From: Larry East (LVE1@inel.gov)
Well, I finally did it; busted my QRP+ while mucking about in its innards!
Managed to short something and took out a switching transistor (2N6036).
Since I am the impatient type and unwilling to wait a week for mail order
delivery (not to mention too cheap to cope with the usual $25 minimum...),
guess I'll fork over 2x the mail-order price for an SK3997 replacement from
the local TV parts house (probably better buy two...). Oh well, win a few,
lose a few...
Mods successfully made so far:
1. Protection for the receiver input (found a better place to stick the
diodes than I described in the Jan. QQ).
2. Removed keying "thump" and "click" (see posting of a few days ago).
3. Reduced receiver "birdies" (ditto above).
4. Changed reverse protection diode from a 1A to a 3A model so that the 2A
fuse will (hopefully) blow before the diode...
5. Changed side-tone injection point so that the side-tone level is not
changed (significantly) by the audio gain control.
6. Added a small pot to control the ALC level and hence SSB output power.
7. Replaced mic gain pot with 5K -- hopefully this will allow higher
impedance mics to give more output (not tested yet).
I was trying to do something about the "AGC thump" on strong signals when
things went amuck... Tried a couple of things that either didn't help or
made the problem worse. Have decided to try a "brute force" series limiter
at the audio filter input -- this should help both the "AGC thump" and
strong adjacent signal overload problems (I hope...).
I plan to write all this up for a future issue of the QRP Quarterly (won't
be the April issue which it is already "in press").
72, Larry W1HUE/7
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