(Almost) The Last of The Mohicans

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.

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.

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.

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.

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.

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.

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.