General Instrument Corp.

Page added November 16, 2018

March 5, 2019 update

     When I purchased this radio it only had one IF transformer, a General Instrument Corporation Type 17-B. I don’t think this transformer type was original for the radio because there were numerous screw holes for each transformer, and the screw patterns do not match the General Instrument transformer. The builder may have actually tried several different brands of transformers to get good results. I initially wanted to restore this radio with a full set of General Instrument transformers. I am now considering to install a set of square Haynes-Griffin transformers.

     Inside view of the General Instrument Corporation Type 17-B IF transformer. All four ends of the copper wires were very brittle and they were broken near the solder joints. The diameter of the wood coil form is only about 1.4 inches. The repaired transformer was peaking at about 190 KC. I tried to bring the frequency down to 50 KC by resonating the primary with a .00068 mFd capacitor but the results were poor. The table below records the pass band characteristics of the transformer without the primary capacitor.

     The table below shows the pass band with a .00062 mFd capacitor in parallel with the primary winding. The relative gain (2.7) was much lower than without the capacitor. What’s more, there was a second peak at 190 KC with a relative gain of 3.0! I can’t imagine how this transformer was ever going to work at the labeled 50 KC.

Restored General Instrument Corporation IF transformer.

June 1, 2019 update - Restoration

     This radio was in need of a set of IF transformers when I purchased it, and, I just happened to have an old set of Haynes-Griffin square IF transformers that were from about the same time period. So I installed the Haynes-Griffin transformers in this set. I think it’s a good marriage! Here is a link to the Haynes-Griffin IF transformers that were used.
     The radio was also in need of some restoration; a little bit more so than what I first thought! I knew that it needed a new lid, some IF transformers, and a good cleaning, but I didn’t know that the front of it had been exposed to some long-term moisture. All the dials were rusted fast to the shafts, and the front panel has got some permanent damage (though it is almost impossible to see in the photos). I like the early, long, superhets, and that is what attracted me to it in the first place. Here are a few particulars of the finished radio:

1. The engraved front panel measures 36” long by 8” high by 3/8” thick.
2. Haynes-Griffin square IF transformers (and possibly oscillator coupler and antenna coupler).
3. Amertran audio transformers (Type AF-6 and Type AF-7)
4. Hammarlund tuning capacitors.
5. Accuratune tuning dials and rheostat dials (early type).
6. General Radio rheostats and potentiometer.
7. Jewel two-range voltmeter.
8. Fleron porcelain tube sockets.
9. Eight tubes.

     Top chassis view of the completed radio. The radio sports a complete set of brass base tipped 01-A tubes, again from about the same time frame that the radio was manufactured (estimated May/June, 1924, chiefly by the Amertran type AF-7 transformer).

     Rear angle view of the chassis. This part of the radio just needed a good cleaning. Most of the parts shown here are the original parts to the radio except for the IF transformers (and some if not all of the tubes). This photo was taken before the tuning capacitor for the filter transformer was installed.

     Hand drawn schematic diagram of the General Instrument Corporation / Haynes-Griffin superheterodyne. The radio has a double-pole double-throw knife switch to use either a loop antenna or a long wire antenna. The radio has regenerative amplification in the first detector only when the antenna coupler and a long wire antenna is used (amplification is controlled via the “tickler” coil). Another unusual feature is the use of plate modulation for the first detector instead of the customary grid injection method. A very interesting early superheterodyne for sure! The Amertran Type AF-7 audio transformer was first announced in the May, 1924, Radio magazine.

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