HEATHKIT SERVICE BULLETINS - GENERAL
Joseph W Lutz
joelutz at JUNO.COM
Wed Jul 9 15:28:47 EDT 1997
OCTOBER 29, 1970
AMATEUR PRODUCTS BULLETIN NO:
GH-4
SBM-102-1
THE ATTACHED MODIFICATION INSTRUCTIONS SHOULD BE FOLLOWED TO CORRECT THE
DRIVER PRESELECTOR PROBLEM OF PEAKING AT A DIFFERENT LOCATION ON RECEIVE
THAN TRANSMIT. THIS IS CAUSED BY THE TUBE MILLER EFFECTS AS EXPLAINED IN
THE MODIFICATION SHEET.
THIS SHOULD BE INSTALLED ON ALL UNITS ABOVE WHEN SERVICING. SB-102 WITH
RUN NUMBERS OF 5446 AND ABOVE SHOULD ALREADY CONTAIN THE MODIFICATION.
INTRODUCTION
THIS MODIFICATION KIT APPLIES TO THE FOLLOWING HEATH TRANSCEIVERS:
1. ALL MODELS HW-100, SB-100, SB-101 AND SB-101W.
2. ANY MODEL SB-102 THAT HAS A NUMBER LOWER THAN 5446 AS THE LAST FOUR
DIGITS OF THE SERIES NUMBER [ON THE BLUE AND WHITE LABEL].
THE PLATE TANK CIRCUIT OF V6, THE SECOND TRANSMITTER MIXER, IS USED IN
THE RECEIVE MODE AS THE PLATE CIRCUIT OF V10, RF AMPLIFIER. DUE TO TUBE
MILLER EFFECTS, ADDITIONAL CAPACITY IS REQUIRED WHEN RECEIVING TO PERMIT
THE DRIVER PRESELECTOR TO PEAK AT THE SAME DIAL SETTING IN BOTH TRANSMIT
AND RECEIVE MODES. THIS MODIFICATION USES AUTOMATIC DIODE SWITCHING TO
ADD THE REQUIRED COMPENSATING CAPACITY,
PARTS LIST
PART QUAN- DESCRIPTION
NO. TITY
------- --------- -------------------
1-26 1 100K OHM, 1/2 WATT RESISTOR
1-35 1 1M OHM, 1/2 WATT RESISTOR
21-33 1 3.3PF DISC CAPACITOR
56-56 1 1N4149 DIODE [CATHODE END MARKED WITH A BAND]
344-50 1 BLACK HOOKUP WIRE
391-34 1 BLUE & WHITE IDENTIFICATION LABEL
431-62 1 3-LUG TERMINAL STRIP
INSTRUCTION SHEET
SOLDER
[ ] REMOVE THE CABINET FROM THE TRANSCEIVER AND TURN THE CHASSIS BOTTOM
SIDE UP.
[ ] REMOVE THE COIL COVER
[ ] IF YOU WISH, TEMPORARILY REMOVE THE SUPPORT RAIL WHICH HOLDS ONE
END OF THE SWITCH BOARDS.
[ ] REFER TO FIGURE 1 AND BEND A SMALL "FOOT" ON THE END OF ONE LEAD OF
THE 100K OHM RESISTOR
[ ] COAT THE "FOOT" WITH A LIBERAL AMOUNT OF SOLDER
[ ] SOLDER THE FOOT ON THE RESISTOR LEAD DIRECTLY TO THE FOIL AT POINT
11 ON THE RF BOARD. NOTE: A WHITE-RED-RED WIRE [AND POSSIBLY OTHER
COMPONENTS] ARE ALREADY SOLDERED TO THIS FOIL.
[ ] CUT THE LEADS OF THE 3.3PF DISC CAPACITOR TO 5/8"
[ ] BEND A 1/8" FOOT ON THE END OF ONE LEAD OF THE DISC CAPACITOR AND
SOLDER THIS FOOT DIRECTLY TO THE FOIL ON THE RF DRIVER CIRCUIT BOARD AT
POINT X AS SHOWN. MAKE SURE THE SOLDER DOES NOT SHORT CIRCUIT THE FOIL
TO THE SWITCH SHIELD.
[ ] CONNECT THE CATHODE [BANDED] END OF THE 1N4149 DIODE TO LUG 2 OF
THE 3-LUG TERMINAL STRIP [S-1]. CONNECT THE OTHER LEAD TO LUG 1 OF THE
TERMINAL STRIP [NS].
[ ] CONNECT THE 1M OHM RESISTOR FROM LUG 1 [NS] TO LUG 3 [NS] OF THE
TERMINAL STRIP.
[ ] COAT THE TERMINAL STRIP FOOT WITH SOLDER.
[ ] REFER TO FIGURE 4 AND SOLDER THE 3-LUG TERMINAL STRIP DIRECTLY TO
THE REAR SIDE [DRIVER GRID SWITCH BOARD SIDE] OF THE FRONT SWITCH SHIELD.
FOLLOW THE DIMENSIONS GIVEN. [[1" IN FROM EDGE OF SHIELD AND 1/2" DOWN
FROM TOP OF SHIELD]].
[ ] CONNECT THE FREE LEAD OF THE 3.3PF CAPACITOR TO LUG 1 OF THE
TERMINAL STRIP [NS].
[ ] CONNECT THE FREE END OF THE 100K OHM RESISTOR TO LUG 1 OF THE
TERMINAL STRIP [S-4]. MAKE SURE THE CAPACITOR AND RESISTOR LEADS DO NOT
TOUCH ANY OTHER WIRES OR COMPONENTS.
[ ] PREPARE A 16" BLACK HOOKUP WIRE BY REMOVING 1/4" OF INSULATION FROM
EACH END OF THE WIRE.
[ ] CONNECT ONE END OF THE BLACK HOOKUP WIRE TO LUG 3 OF THE TERMINAL
STRIP [S-2].
[ ] NOTE: TWO SETS OF STEPS FOLLOW. USE ONLY THOSE STEPS APPLYING TO
YOUR TRANSCEIVER.
MODELS WITH "SB-" PREFIX:
[ ] REFER TO FIGURE 5 AND ROUTE THE BLACK HOOKUP WIRE OVER THE
BANDSWITCH SHAFT, DOWN THROUGH GROMMET CD, AND BACK ALONG THE WIRING
HARNESS TO LUG 1 OF THE BIAS ADJUST CONTROL. POSITION THE WIRE AGAINST
THE SWITCH SHIELD.
[ ] MELT THE SOLDER ON LUG 1 OF THE BIAS ADJUST CONTROL AND PUSH THE
BARE END OF THE BLACK HOOKUP WIRE THROUGH THE OPENING IN THE LUG. AFTER
THE SOLDER HAS COOLED, TUG ON THE WIRE TO MAKE SURE IT IS SECURELY
CONNECTED.
PROCEED TO THE "FINAL ASSEMBLY."
MODEL HW-100:
[ ] REFER TO FIGURE 6 AND ROUTE THE HOOKUP WIRE OVER THE SWITCH SHAFT,
THROUGH GROMMET CD, AND ALONG THE WIRING HARNESS TO BIAS CONTROL CT.
[ ] MELT THE SOLDER ON LUG 1 OF CONTROL CT AND PUSH THE BARE END OF THE
HOOKUP WIRE THROUGH THE OPENING IN THE LUG. AFTER THE SOLDER HAS COOLED,
TUG ON THE WIRE TO MAKE SURE IT IS SECURELY CONNECTED.
FINAL ASSEMBLY
NOTE: YOU CAN SECURE THE HOOKUP WIRE TO THE WIRING HARNESS WITH
ELECTRICAL TAPE OR WITH SHORT PICES OF HOOKUP WIRE.
[ ] IF IT WAS REMOVED, REPLACE THE SUPPORT RAIL AND SECURE IT WITH THE
HARDWARE PREVIOUSLY REMOVED. MAKE SURE ALL SWITCH BOARDS AND SHIELDS FIT
INTO THE PROPER SLOTS IN THE COMB ON THE SUPPORT RAIL.
[ ] REPLACE THE COIL COVER. MAKE SURE THE GROUNDING CLIPS ON THE UNDER
SIDE OF THE COVER FIT OVER THE SWITCH SHIELDS.
[ ] REFER TO THE ALIGNMENT SECTION OF YOUR ASSEMBLY MANUAL AND PEAK THE
DRIVER GRID AND DRIVER PLATE COILS.
[ ] REPLACE THE TRANSCEIVER CABINET.
[ ] CAREFULLY PEEL AWAY THE BACKING PAPER FROM THE BLUE AND WHITE
INDENTIFICATION LABEL. THEN PRESS THE LABEL ONTO THE REAR OF THE
CABINET. BE SURE TO REFER TO THE NUMBERS ON THIS LABEL IN ANY
COMMUNICATIONS YOU HAVE WITH THE HEATHKIT COMPANY ABOUT THIS KIT.
CIRCUIT DESCRIPTION
A NEGATIVE VOLTAGE IS ALWAYS APPLIED TO THE ANODE OF D907 FROM THE BIAS
ADJUST CONTROL THROUGH RESISTOR R954. WHEN RECEIVING, A HIGHER POSITIVE
VOLTAGE IS APPLIED TO THE ANODE OF D907 FROM THE SCREEN CIRCUIT OF V1
THROUGH RESISTOR R955. AS ITS ANODE IS NOW POSITIVE, THE DIODE CONDUCTS
AND ACTS AS A CLOSED SWITCH TO SUPLLY A GROUND TO C955. THIS ACTION
PLACES THE CAPACITOR IN PARALLEL WITH C421B AND ADDS CAPACITY TO THE
PLATE TUNED CIRCUIT.
IN THE TRANSMIT MODE, THE POSITIVE VOLTAGE IS REMOVED BY THE OPENING OF
CONTACTS 3 AND 11 OF RL2. THE REMAINING NEGATIVE VOLTAGE PREVENTS D907
FROM CONDUCTING AND IT CONSEQUENTLY ACTS AS AN OPEN SWITCH, REMOVING THE
GROUND FROM C955. THE CAPACITANCE OF C955 IS THEREFORE REMOVED FROM THE
PLATE CIRCUIT OF V6.
------------------------------------------------------------------------------------------------------------------
THIS CONCLUDES 'GENERAL BULLETINS' GH-1 THROUGH GH-4.
------------------------------------------------------------------------------------------------------------------
73 de JOE
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QWCA - NCVA - SOWP - FISTS
Gordonsville, Va 22942 (Orange County)
Looking for: Heathkit HR/HX-20, MR/MT-1,
Collins 516F-2, 312B-4, EFJ TR Switch
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