I got an HW-8 question recently from Jeff Grudin, AC6KW. He picked
one up a few months ago and did some work to get it going--replaced a
couple of transistors as well as a missing audio board. He said he was
getting about 2 watts out (which is about right) but couldn't seem to
work anyone. He phoned his daughter and had her try to work him
while she stayed on the phone. He discovered that the TX and RX
frequencies were off by about 5 kHz.
Jeff, the reason you don't see an obvious way to adjust the difference is
that there is none. The offset is fixed. You can find a description of it
on page 75 of the manual, under "VFO". Looking at the left side of
the schematic, Q2 is the VFO. The source has a resistor to ground, but
it also has capacitor C55, a 5 pF ceramic disk, connected to switching
diode D11. In receive, D11 is not conducting and C55 has no effect.
In TX it is supplied with voltage by Q13, which also drives the T/R
relay (both of those are in the upper right corner of the schematic).
The diode conducts and C55 is shorted to ground, changing the VFO
frequency slightly. I mentioned this some time ago in my Idea
Exchange column in the QRP Quarterly, when someone asked about
changing the TX/RX offset a little. In your case, there's a good chance
that the capacitor has either changed value significantly, is defective,
or has even been replaced with a different value. (After all, you did
say that the rig had a couple bad transistors and a missing audio amp
board, so it did have problems and someone had obviously been inside
already.)
Looking down at the component side of the PCB with the front of the
rig facing you, there are 6 components in front of the VFO coil shield
can, between the 21 MHz pushbutton switch and VFO tuning
capacitor. The third one back from the front is a ceramic disk cap,
between some resistors--that's C55. Make sure it's undamaged and of
the proper value. If it doesn't fix the problem, you might check out
D11 (the diode in the front of the line of parts); I don't know if a
partial failure of that could give you this symptom, but it's a straw to
grasp at if the capacitor checks out.
You also mentioned that you were getting 2 watts out, which is about
right. Sometimes people see a lot less than that on 80 and/or 40, and
tuning up the rig refuses to fix it. Here's a plug for a couple of my
articles on the ftp server of lehigh.edu. The HW-8 uses "oddball"
matching networks for the final amp, not pi net low pass filters that
we're used to seeing. For 80 and 40 meters they use low permeability
ferrites, with ui of 40. These cores can sometimes go bad with the net
effect that power output drops, and no matter how much you tune up
the rig you won't get full power on 80 and/or 40. (They use powdered
irons on the two higher bands, and you won't see the problem there.)
I detailed this in the QRP Quarterly several years ago, and reported
some related experiments on cores later in my Idea Exchange column.
I'm sure none of it will be any surprise to any engineers who've done
extensive work with magnetic cores :-) Since I first stumbled on this
problem of the cores going bad, I have had ten confirmed fixes, several
of those by my own hand.
If interested, you can find the articles at the ftp area of lehigh.edu
under pub, listserv, qrp-l, articles, The file names are something like
badhw8cores.mcq and zapcores.mcq. When you go to download them,
note that there is also a .z tacked onto the end of the file names, after
the .mcq extension (which just identifies them as my files). That
indicates that they are stored on the machine in a compressed format.
I'm not sure exactly what it is, but suspect it's a UNIX utility of some
sort. Download the file with the .z on the end and you will be
responsible for decompressing it yourself on your own machine. If you
download it without the .z, it will decompress it and then spit it out,
and you'll be able to read the text without having to process it further.
(This is NOT the familiar PKZIP that everyone knows.) Even if you
don't have an HW-8, the information about cores could prove
interesting reading.
73 and Queue Our Pea DE WA8MCQ wa8mcq@abs.net
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