HEATHKIT SERVICE BULLETINS - CONT.
Joseph W Lutz
joelutz at JUNO.COM
Fri Jun 20 03:26:38 EDT 1997
Moving right along:
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February 16, 1973
HW-7 Bulletin No:
QRP Transceiver HW-7-1
Dail Rubbing
To Prevent the dial rubbing against the front panel the following change
has been made in production. Replae the [4] 253-27 flat washers with two
aluminum spacers, Part No: 255-1.
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February 16, 1973
HW-7 Bulletin No:
QRP Transceiver HW-7-2
Broadcast Interference
In spite of the article in the January issue of QST, page 48, we do not
plan to make a modification kit for this problem. However, we plan to
track the identity of all purchaser's & mail the information & parts to
them individually. To service those we miss [retail sales primarily],
the attached information sheet will suffice. The parts should be
furnished at no charge. Only those with serial numbers starting '002'
require the change. Others already have them in the kit itself.
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February 16, 1973
HW-7 Bulletin No:
QRP Transceiver HW-7-3
Low Audio Level - Receiver
Replace R411 [10K Ohm] Part # 1-20 with 1000 Ohm, Part #1-9. This is a
production change which should be made in all kits with SN's starting
with '002'.
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February 16, 1973
HW-7 Bulletin No:
QRP Transceiver HW-7-4
Service Hints
RECEIVER: The receiver section of the HW-7 is basically a direct
conversion type circuit. The incoming signal is mixed with the
on-frequency VFO signal to provide audio output.
The audio is filtered by the lowpass audio filter & coupled to the audio
IC which has approximately 100db of gain. A certain amount of microphony
is normal for this type of circuitry.
Normal sensitivity for this receiver is less than 1uv will provide a
readable signal. This is normal since all Protos & Field Test Units
showed much better sensitivity.
Typical RF voltage readings at the detector FET Q1 are .6 to 1 volt RMS
nominal measured on Boonton 91-C meter. Any injection appreciably lass
than .4 volt RMS will give a loss of sensitivity. NOTE: This voltge is
not a pure sine wave.
When Receiveing a signal, the front panel preselector control must be
carefully peaked in the designated areas.
VFO/DOUBLER/TRIPLER
The Colpitts oscillator operates on 3.5 to 3.6 MHZ and doubled to 7.0 to
7.2 MHZ for 40 Meter operation. For 20 & 15 Meter operation, the
oscillator runs at 7.0 to 7.1 MHZ & doubled for 20 meter [14.0 to 14.2
MHZ] & tripled for 15 meters [21.0 to 21.3 MHZ]. Following are typical
RF readings:
Gate of Q3 = Approx. 1 Volt RMS [Sine wave]
Base of Q4 = Approx. .8 Volt RMS [Approx. Sine wave]
Collector of Q4 = Sine wave with harmonics
OSC./DRIVER & RF AMPLIFIER
Base of Q5 [xmit] = 1 to 2.5 Volts RMS [not Sine wave]
Base of Q6, Q7 = 1.5 to 2.5 Volts RMS [not Sine wave]
RF output across 50 Ohm load should be approximately 10 Volts RMS [Sine
wave for all bands].
Possible problem area in transmitter may be two extremely mis-matched out
transistors [high gain with low gain]. This may cause one transistor to
"hog" all the current thereby destroying itself. When this happens, also
check zener diode ZD1 for possible open circuit. If instability is a
problem, also check ZD1 for open circuit.
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May 3, 1974
HW-7 Bulletin No:
QRP Transceiver HW-7-5
Audio ["popcorn"] Noise Reduction
The following modification will reduce the noise level of the CA-3035V1
audio IC considerably:
1] Connect a 220K [PN 1-29] resistor and a .1uf [PN 21-95] disc IN
SERIES from pin 4 to pin 5 of the CA-3035V1 on the foil side of the
board.
2] Connect a 1 uf Electrolytic [PN 25-197] from pin 6 of the CA-3035V1
to the ground foil between pins 2 & 8.
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July 12, 1974
HW-7 Bulletin No:
QRP Transceiver HW-7-6
Sensitivity Improvement
1] Jumper a small wire across C6 [100pf] on the foil side of the board.
2] Remove R1 [100K Resistor].
NOTE: If the unit fails to operate, or there is no increase in
sensitivity with this resistor removed, it should be resinstalled in the
circuit.
These circuit changes are to be made only as needed.
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March 26, 1975
HW-7 Bulletin No:
QRP Transceiver HW-7-7
Pulse Oscillation on 40 Meters
If the HW-7 has an oscillator problem, check to see if Q2 is a Teledyne
device rather than a Motorola.
To prevent the circuit frompulse oscillating, install a ferrite bead [PN
475-10] on the gate lead if Q2 is a Teledyne type.
HW-7 Modifications
A. Remove & discard capacitors C-5, C-6, C-8, C-9.
B. Replace C-5 & C-9 with .22uf mylar capacitors.
A. Lift coax from point A on circuit board.
B. Install 100pf mica capacitor between center conductor of coax and
point A. [Improves BCB rejection].
A. Install heat sinks on transistors using silicone grease for PA
protection.
PARTS LIST
[2] .22UF 27-85
[1] 100PF 20-102
[2] #4-40X1/2" SCREW 250-52
[2] #4 LOCKWASHER 254-9
[2] #4-40 NUT 252-15
[1] SILICONE GREASE 352-13
[2] HEAT SINK PLATE 205-1436
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April 17, 1975
HW-7 Bulletin No:
QRP Transceiver HW-7-8
Modifications F/U/W the HD-1410 Keyer
The HW-7 keying circuit was designed to be compatible with the HD-10
keyer. This is the reason that the key jack has the tip contact
grounded. Two changes should be made to the HW-7 to allow use with the
HD-1410:
A] The two wires going to the HW-7 key jack should be reversed.
B] R39 should be changed from 470 Ohm to 4700 Ohm.
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That's it for HW-7.
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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