Heathkit Service Bulletin - HW-8 (Complete)

Joseph W Lutz joelutz at JUNO.COM
Sat Aug 2 22:10:09 EDT 1997

                                                       October 28, 1975
                         Bulletin No.
CW Transceiver                                              HW-8-1
                                                           Service Data

Operating Characteristics

1.  Receiver preselector peaking is done with the preselector (C301) FCW
(Minimum C) resulting in only broad peaks or no peaks being found when
this control is adjusted.

Also, maximum sensitivity may not coincide with maximum noise when
adjusting the preselector.  For example, in trying to locate a Generator
Signal, the preselector would be tuned for maximum noise.  When the
signal is found and the preselector adjusted for a miximum signal, the
defference between the maximum noise point and the noise level at the
maximum signal point could vary as much as 6 db (typical).  Therefore, be
sure to peak the preselector on the signal and not on the noise.

2.  Internal spurious signals may be found at 3.55MHZ, 7.1MHZ & 14.1MHZ.
The levels are approximately .7 to 8 uv.

3.  Receiver sensitivity will increase when the selectivity switch is
switched from the wide to the narrow position.  This is due to the added
gain of the bandpass filter IC-2B and it's associated circuity.

4.  Microphonic levels as compared to the HW-7 have been reduced greatly,
although some still appear on the 80 Meter band.  These microphonics are
noticeable at the lower and center areas of the band when more capacity
is required from the preselector.

5.  The receiver tends to pick up more hum on 15 Meters than on any other
band.  The hum levels on 15 Meters is much less than those present on the


-  Sensitivity:  1uv or less for 10 db S+N/N

   Typical Sensitivity:   80 Meters     -   .5uv
                                         40 Meters     -   .6uv
                                         20 Meters     -   .7uv
                                         15 Meters     -   .7uv

-  Selectivity:      Wide          -  750 HZ at 6 db down.
                              Norrow     -   375 HZ at 6 db down.

A rough check of the wide and narrow BPF can be made by tuning the
receiver to a signal so that a high-pitched beat note is heard in the
wide position.  Switching to the narrow position should produce a
noticeable decrease in the audio output.

-  Dial Tracking:   Within one dial division.

                                                         Service Notes

1.  Poor Sensitivity:  Poor sensitivity can be caused by either Q1 (Part
# 417-169) or IC-1 (Part # 442-96).  Poor sensitivity on one band only is
usually caused by Q1.

2.  15 Meter Band Adjustments:  The adjustments may be more critical on
the 15 meter band than on other bands.  It may be necessary to set the
mixer coil, check the power output & sensitivity and then reset the mixer
coil.  Check the high & low end of this band and adjust coil L6 to bring
up the end that has the lower output.

3.  Receiver Oscillates on the 80 Meter Band:  When operating the
transceiver at DC input voltages greater than 12.5 VDC, the receiver may
oscillate at points throughout the 80 meter band.  To correct this
problem connect a 10 K  ohm resistor (Part # 1-9-12) across the 80 meter
mixer coil L13.  This resistor is soldered to the coil terminals on top
of the circuit board.  Install this resistor only when needed.

The receiver should not produce undesired oscillations - - - except at
internal spurious frequencies listed in operating characteristics -- when
the DC input voltage is raised to as much as 15 VDC.

                                                            Final Check

The following is a list of physical & functional checks that must be made
before returning the transceiver to the customer:

Physical Checks:
-  All hardware installed & tightened
-  Cabinet & windows clean
-  Plastic feet installed
-  Controls & switches operate smoothly
-  Knobs properly indexed & secure
-  Mark to the left of 0 on dial is aligned with black line on window.
Mark stays aligned when tuning knob is turned further clockwise.
-  Shake test - - - nothing rattles inside.
-  Paperwork in order.

Functional Checks:
-  TX power output - 1 watt or greater on all bands.  Connect a 50 ohm
non-reactive load to the antenna jack.  Tune the dial to 150, key the
transmitter and measure the RF voltage across the load.  The unit is
within specs if the RFV is 7V rms or greater.

-  Typical powr output:            80 Meters    -    1.5 W
                                                      40 Meters    -
1.5 W
                                                      20 Meters    -
1.5 W
                                                      15 Meters    -
1.5 W

-  TX frequency offset:  Approximately 750HZ lower than the Receive
frequency.  Check what transmitter frequency is shifting below the
receive frequency by approximately 750HZ +/- 200HZ.  The amount of
frequency offset does change from band to band.

-  Sidetone is heard in speaker or headphones when the transmitter is

                        April 6, 1976
HW-8                                            Bulletin No:
CW Transceiver                                  HW-8-2

                        Unit Chirps

A slight chirp problem has shown up on some of the HW-8 units which are
now in the field.  The problem has been traced to the hetrodyne
oscillator switching diodes which are apparently not isolating
sufficiently in the off bands.

We are therefore changing the heterodyne oscillator switching diodes D22
through D29 from PN 56-24 to PN 56-56.  The 56-56 diode has less
capacitance and probides better isolation.

Second production lot will have the 56-56 diode.
                        April 29, 1976
HW-8                                            Bulletin No:
CW Transceiver                                  HW-8-3

                VFO Alignment with Frequency Counter

Using the following procedure to adjust the VFO with a frequency counter
instaed of a receiver:

1.  Connect the frequency counter probe through a 47 PF [approx]
capacitor to the emitter of transistor Q3.  Connect the counter's ground
lead to the chassis.

2.  Turn the HW-8 on and allow it to warm up for at least 30 minutes
before you proceed.

3.  Release all pushbuttons to out position.

4.  Turn the HW-8 tuning dial to 0.

5.  Use an insulated screwdriver and adjust C302B [on the side of the
tuning capacitor] until the counter reads 8.895 MHZ.

6.  Turn the HW-8 turning dial to 250.

7.  Use a large plastic alignment tool and adjust the slug in coil L9
until the counter reads 8.645 MHZ.

8.  Repeat steps 4 through 7 several times until the counter reads
properly with no adjustment at each end of the dial.
                        July 13, 1976
HW-8                                            Bulletin No:
CW Transceiver                                  HW-8-4

                        Q11 Installation

Q11, an S2091 tansistor [PN 417-116], may be either of two body styles.
Be sure this transistor is installed as shown in the drawing below.

((The small flat transistor matches small flat to flat of PC board; the
larger transistor the flat is "opposite" the flat of the PC board.  Both
types have leads 1/4" from PC board to components)).
                        November 15, 1976
HW-8                                            Bulletin No:
CW Transceiver                                  HW-8-5

                     Carrier Stays On, Will Not Turn Off With Key Open

Cure:  The wires at points K and XX on the circuit board my be
interchanged.  Q8 will not shut off when the key is open.
                        December 2, 1976
HW-8                                            Bulletin No:
CW Transceiver                                  HW-8-6

        Poor Sensitivity on 80, 40, 15 Meter Bands; Preselector Peaks
                        At The Wrong Position

Check for proper installation of L1, L2, L3 and L4. These coils have been
found to be installed in reverse order causing apparent good sensitivity
on 20 meters, but poor sensitivity on 80, 40 and 15 meters.
                        June 5, 1978
HW-8                                            Bulletin No:
QRP Transceiver                                 HW-8-9

                         Voltage Chart Correction

The cirucit board voltage chart in the HW-8 manual [PN 595-1754-07], page
80, shows IC2 pin numbers 1 and 14 interchanged.  The voltages, as shown,
are correct.

Future manuals will be correct
                        November 20, 1978
HW-8                                            Bulletin No:
QRP Transceiver                                 HW-8-10

             PN 417-240 FET's supplied with shorting wire on leads

This unti may have been shipped with a shorting wire around the leads of
the PN 417-240 device.  The manual does not give instructions to the
customer for the removal of the shorting wire.

When servicing this product, check for the possibility of the shorting
wire still installed on this device.

The manual is being inserted with the proper instructions concerning the
removal of the shorting wire.
-------------------------------------------------------------------------------------------------------------------                             September
19, 1979
HW-8                                            Bulletin No:
QRP Transceiver                                 HW-8-11

        Spurs Heard as Receive is Tuned Through Strong Signals
                      [50uv or more] all Bands

This problem sounds almost like front-end instability.  Check for proper
installation of Q201, audio output transistor; it may be installed
backwards.  This may be overlooked during initial inspection because Q201
is hidden under C203, and audio stages appear to operate normally on CW.
Harmonics generated by Q201 beat with VFO to generate spurs.

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