At this session we had about 23 people with about 10 radios brought in. About 8 of the radios left in playing condition. The remainder were diagnosed and a plan established for completing the repair job at home. As usual, the ones brought in by the more experienced members were the toughest, because they had already spent a lot of time trying to get them working. The tougher ones were often those that had been previously mis-wired by someone else or in the recent process of attempting a repair. A particular set the author was working on, a Majestic Model 50, had a number of problems – the worst being open I.F. transformers. One I.F. transformer had an open secondary winding. After rigging an R/C-coupling patch on that stage, it turned out that another one was bad. As is typical for a Majestic, the bad parts were difficult to get access to. We used a Micronta signal injector (see Author’s Note, below) to find the dead stages. As we ran out of time, we were getting signal all the way through from the 1 ^st I.F. to the speaker. The local oscillator was working OK as indicated by a strong negative bias on the oscillator tube grid.

All through the session, there would be the sound of another set coming to life (not always with really good sound). Besides the learning experience, a number of people were happy to leave with a working radio or at least the knowledge of how to make it work. There was a lot of exchange of ideas among the "experts" on each radio to help locate the problems. Once again, Gary Reeves cranked out schematics, as needed, from the computer.

There was a good mix of experience-level, and those that are fairly new at this hobby and were there to learn gained a lot from the session. Of course, even those with a lot of experience can always learn more "tricks of the trade", by observing how other experts tackle a problem and what equipment they employ in their troubleshooting, and how they use it to advantage. Besides our Repair Sessions, our NOTES FROM THE BENCH articles are a good source of tips and tricks.

Author’s Note : The Micronta (Radio Shack) signal injector is a simple one-transistor oscillator in a hand-held case – powered by 6 volts from four AA batteries. It dates from the early ‘60’s. It has a pushbutton, a little red indicator light (this was made before LED’s existed) to tell you it’s working, and a probe to touch to the point in the circuit where you want to inject a test signal. The oscillator has very strong feedback so it generates a signal that is very rich in harmonics, at about 1KC. It is so rich in harmonics that you can hear the 1KC tone with the signal applied anywhere from the grid of the audio output tube (or transistor), all the way back to the antenna – including I.F. stages. It will even make a video pattern on a TV. Your body acts as a "ground plane" for the signal. As you work your way back stage-by-stage, the signal gets louder and louder, unless there is a dead stage. If so, you have pinpointed the problem area. Of course it will not tell you if the local oscillator is dead, but there are easy ways to find that out, anyway. ("What way is that?", you say - The local oscillator will always have a grid-to-cathode negative bias generated by the oscillation. If it’s zero or positive, the oscillator is dead. This tool has helped find problems in many radios, especially back during the time when transistor radios were an expensive item and worth the trouble to repair. Many of them were the transistor portables and pocket radios - made for large pockets. The real advantage of the signal injector is that you don’t have to worry about tuning a signal generator to the right frequency in order to get a response, when you’re simply looking for a dead stage.

See you next session.