While I now tend to
favour European transistorized radios made in the 1960’s and 1970’s, I can
remember as a kid lusting after shortwave receivers like the Heathkit Mohican.
Alas, the price was too high for a teenager with an allowance and no job, so I
had to settle for a Knight-Kit Star Roamer at the time.
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| My Restored Heathkit Mohican GC-1A |
Fast forward to last
fall, and there was a sad (correction…pathetic) looking wreck of a Mohican
GC-1A at a local ham flea market, beckoning to me. For $10, I thought I would take
a chance on it, even though the S-meter and antenna were missing and the case
and chrome knobs were badly pitted. One promising thing was that the dual
sliderule dials were clean and intact, and the tuning knobs and pointers seemed
to work OK.
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| First IF Transformer now shielded and covering the hole in the board |
Opening it up,
however, revealed more surprises. There was the first IF transformer, sans
outer shield, suspended by a few wires above a gaping hole in the board. Did
something explode in there, or did the builder get frustrated and punch a hole
through it with a screwdriver? Looking further down the board, I couldn’t help
but notice a couple of trimmer pots, also suspended by wires above the board.
This was going to require a schematic to figure out what was going on, so I
Googled the manual and downloaded it.
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| Series-resonant 455 kHz filters (circled) |
As I was to discover,
someone in their lack of wisdom decided to replace two interstage ceramic IF
filters with those trimmer pots (!). But it doesn’t stop there. The AVC switch
and the dial lights were also miswired. It dawned on me that someone with just
enough knowledge to be dangerous must have had a go at this radio as a second or
third owner, because the construction was otherwise good. Maybe when they discovered that pots
don’t work well as bandpass filters, they decided to take revenge on the IF
transformer? While I didn’t have any three-terminal ceramic filters on hand, I
did have some series-resonant two-terminal types that I used as interstage
couplers in those same locations. Result.
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| Battery Pack |
So, after sanding down
the steel case, priming it, and applying several coats of an automotive aerosol
paint (guesswork involved on the original colour), it looks great.
Surprisingly, the knobs cleaned right up with a damp cloth, and continue to
shine like new. Of course, the battery pack was somewhat corroded, but now
functions well. With 8 C cells loaded, I have to say this radio weighs enough
to make a good negative-buoyancy marine stabilizer (boat anchor), thanks
largely to the steel construction.
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| S-Meter & AVC Switch |
Getting original
components is near impossible, so I settled on a replacement telescoping
antenna, and had to enlarge the S-meter opening slightly to accommodate one
from a cannibalized CB set. To make the meter function logically and properly,
I had to reverse the scale card inside the meter and pad it down with a shunt
resistor.
Apart from re-capping,
one of the last tasks was alignment. Heathkit includes an involved procedure in
their manual, and it’s worth following. The only oddity is that the IF tuned
fine at 435 kHz, but I couldn’t get it to go to 455 kHz. This caused a bit of
head scratching when it came to identifying the image frequencies, but as long
as the alignment is done with this knowledge, it’s not a problem.
After completing the
alignment, it was time to hoist the antenna and play. Intially, I was
disappointed with the gravelly quality of the audio, and SSB sounded somewhat
unintelligible at times. My first thought was that the IF alignment was poor
and/or the BFO needed tweaking. With no joy there, I looked at the Mohican’s demodulated
audio from my RF generator on the ‘scope, and noticed crossover distortion at
the speaker. By padding the bias resistors on the bases of the push-pull audio output
transistors, the sound is now quite sweet on both AM and SSB. It took a lot of
padding, though, so the old germanium transistors were probably getting a bit
tired.
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| Alignment trimmer caps and coils for local oscillator, mixer and front end |
Heathkit marketed this
radio from the early 1960’s up until about 1968. While it’s not the hottest
receiver by today’s standards, it is surpisingly sensitive and stable. That
probably explains how this single model remained popular througout nearly a
decade. And while I lived with its challenges for several months, now that it
is fully functional, the nostalgic value is going to keep it in my collection
for some time to come.
