Hello group.
I received the AGC hiss modification info from T-T today.
I haven't performed the modifications yet, so cannot comment on the =
outcome.
Here is the scanned text:
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MODEL 562, OMNI V
PBT/IF-AF MODIFICATION
EFFECTIVE JUNE 1990 PRODUCTION
The purpose of this change was to "fine tune" AGC performance
and reduce background hiss that can be noticed under weak cw
signal conditions with extreme settings of the TONE and BP
controls. The purpose of this bulletin is to keep you informed.
The modification is not recommended because it fails the test
of performance improvement vs. the effort required.
MODIFICATION SUMMARY
PBT BOARD: C40, change from 1200pf to 750pf.
(81460) C41, change from 360pf to 330pf.
C51, change from 5pf to 27uh in series with .0luf. =20
R46, change from 10k to 3.3k. =20
IF/AF BOARD: R5, change from 4.7k to 1k.
(81462)
PROCEDURE
1. Remove bottom cover and shield.
2. Locate the PBT board (81460), right center of chassis.
3. Unplug all cables from PBT board. (38,39,41,42,43)
4. Remove the 6 mounting screws from the board/chassis.
5. Remove and replace components as listed the summary, above.
6. Re-install the board and cables.
7. Locate the IF/AF board in front of the PBT board.
8. Unplug all cables from IF/AF board. (43,44,46,47,48,49,50,
51,53,54,55,56,57,0
9. Remove the 5 mounting screws from the board/chassis.
10. Remove and replace R5, as shown in the summary above.
11. Re-install board and all connections.
ALIGNMENT PROCEDURE
1. Power up radio. Inject a weak signal through the antenna
connector. Adjust signal level so that the S-meter is just
deflected with the receiver tuned to the signal frequency. Any
frequency is fine,
2. On the PBT board, adjust coils L18, L19 and L20 for maximum
strength on the receiver S-meter. These coils will interact so
you will want to go though the adjustment process several times.
3. Calibrate input signal to 50uv. On the IF/AF board, adjust
R45 for an S9 reading on the S-meter.
FINALLY...
1. Check transmitter and receiver for normal operation. If
there are any malfunctions, re-check all cable connections.
2. Install bottom shield and bottom cover.
TEN-TEC, INC.
1185 Dolly Parton Parkway
Sevierville, TN 37862
U.S.A.
SERVICE....... 615-428-0364
SWITCHBOARD... 615-453-7172
FAX........... 615-428-4483
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Vy 73 Paul MW0CDO
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