Heathkit GC-1A Mohican Receiver

The Mohican was Heath's first all transistor general coverage shortwave and broadcast receiver. Intended primarily for the short-wave listener and for portability, it includes calibrated bandspread for the ham bands and a BFO for copying code and SSB. The copyright date on the GC-1A manual is 1960 which was the year of introduction for the earlier GC-1 version of the receiver. The first ad found in Radio-Electronics magazine was in March 1960. The GC-1 was advertised in that and other popular magazines until October 1960. I do not know what improvements were made for the GC-1A but the GC-1A manual notes a printing date of May 28, 1962 despite its 1960 copyright date. The GC-1A was available from 1961 until 1968. Apparently Heath made a kit of parts available to upgrade the performance of the early GC-1 "for Mohican owners who have experienced excessive distortion in the audio system or difficulty in obtaining stable operation in the higher frequencies." I am assuming the GC-1A includes those improvements. If you have first-hand information on the Heath upgrade kit for the GC-1, please let me know.

Price of the GC-1A kit was $109.95 in this Christmas 1961 catalog ad. Price in the 1966 catalog (below) was $89.50

The outward design of the GC-1A Mohican reflects Heath's "chrome-knob, green cabinet, and tribal name" era for ham equipment which was primarily 1959 to 1963. The GC-1A is the only chrome-knob tribal-name device still offered by Heath in 1967-68, making the "Mohican" the last of that design series.

Repairs
This GC-1A Mohican was purchased at a local auction. It did not work at all. The telescoping antenna and its large grommet were missing. The set had the optional XP-2 117 volt AC adapter but was missing the battery pack.

GC-1A Mohican ad in the 1966 Heathkit catalog

Repairs
The bandswitch would not turn. I used deoxit on the bushing and managed to free it. Deoxit was also used sparingly on the bandswitch contacts, all the other controls, and the transistor sockets.

I was about to replace the defective RF gain control but was able to open it and repair it mechanically.

For initial tests, I used a separate 12 volt supply. Because all the transistors are PNP, the set is positive ground. Care must be taken with polarity. The external screw-terminal muting contacts actually open the power supply feed to the receiver for all functions except the pilot lights. I found that to be a convenient place to connect the negative power supply feed. The positive feed was simply attached to the ground screw next to the external antenna terminal.

Despite now having adequate voltage, the set did not function on any band. This was quickly traced to the local oscillator not functioning. I initially thought that the bandswitch contacts might be at fault and wondered if the set had ever worked in the past. Because the transistors are socketed, I swapped the oscillator transistor with the mixer. No changes. Voltage measurements on the transistor did not show any defects. Since I was working with nearly unobtanium high-frequency-capable germanium transistors, I was doubly careful. What threw me was that voltages on the base, emitter and collector were correct, at least according to my 1 megohm-per-volt digital meter. Convinced that the transistor itself was good despite some normal germanium transistor leakage, I finally pulled the transistor and did some resistance tests. That quickly located the problem. The 1000 ohm emitter resistor was open! It looked OK and was sandwiched tightly under the transistor socket. Pulling the resistor revealed the real problem. One joint, while covered in solder flux, had apparently never been soldered! The set was otherwise well constructed. I suspect the set may have been intermittent much of its life if it worked at all. I assume there was enough leakage in the germanium transistor to give correct or nearly correct voltage readings.

Early on, I noticed that one of the bypass electrolytics in the audio section was missing. Replacing it had the expected effect of greater audio gain.

Alignment
After repairs, the set was obviously in need of alignment. Both the tracking and sensitivity depended upon the dial setting. The Mohican is not an easy set to align given its ceramic filters. The procedure in the manual should be followed in the exact sequence.

Maurice in Britain has copied the relevant pages for schematic, alignment and dial stringing from his Mohican manual .

Once aligned, the set is actually quite sensitive, but takes some getting used to especially the BFO and RF gain control action when listening to SSB.

That missing antenna
Given the low probability of finding an original telescoping antenna, I replaced the missing one with a generic one. Not having a large rubber grommet, I drilled an appropriate opening in a chrome hole plug and inserted a smaller grommet into that opening.

Performance
Despite its size and its ten transistors, the GC-1A takes very little power. Compared to any tube type device, this all-solid-state device generates no discernible heat which helps greatly with stability. The Mohican has some backlash on the bandspread control that is annoying when tuning SSB, but that could be due to improper tension on the dial cord.

The Heath ad suggests using the Mohican as a back-up ham receiver. That is certainly possible on the lower frequency bands.

A simple mod
The 117 volt power supply is a rather simple design. Given modern higher socket voltages, I decided to place one or two diodes such as the handy 1N4004 across the muting contacts. That lowers the voltage by 0.6 volt per diode and also gives me a convenient point to feed the radio with an external 12 volt source. The diode(s) can also prevent damage in case of improper polarity. Wiring the diode(s) internally is probably the best solution.

Your experiences?
The Heathkit Mohican has been both praised and panned by users. I suspect the difficulty in alignment and the need to properly clean all the contacts including the transistor sockets may be part of the problem. Let me know your experiences with the Mohican.

Specifications showing transistors used in the Mohican GC-1A

6-14-10