Notes from the July 15, 2006 meeting/repair session

This year’s workshop saw a very unusual "patient". It was the first TV that we ever tackled, but one of the simplest ever made – a 1948 Pilot Radio 3 inch set belonging to Jonathan Stanley. These sets are rare because they came out in the very early days of TV. They were the first TV to sell under $100.00 (price $99.95). This set had already been totally re-capped by Jonathan, and he had adapted a 3 inch ‘scope tube to produce a picture, albeit a green one. The sound section resisted efforts to align it because the I.F. stage wanted to break into oscillation. This was a very subtle problem that stemmed from connecting a new capacitor to the wrong (adjacent) heater pin. (Considering the huge number of capacitors, this was an easily made error). This allowed coupling through a sneak path that included the capacitance between the heater and cathode of the IF tube and the downstream tube grid-to-cathode-to-heater. A rigorous tracing of circuit components revealed the problem, and correcting it allowed the alignment process to succeed. (See photo of myself and Cleo Cherryholmes double-checking the wiring around the offending, oscillating, IF stage. Also, see photo of Jonathan fixing the problem). Once the problem was corrected, the alignment process was successful. Because TV alignment frequencies are fairly critical, we used a digital frequency counter to make sure the signal generator frequency settings were exact. Finally, there was sound with the picture!

Other members worked on sets of various vintage, including some AA5 Bakelite radios and earlier wooden cabinet sets, including an AC set. President Jim Sargent evaluated a radio (see photo) that was brought in as a result of our invitation to the public to bring in their antique radios for an (unofficial) appraisal, as to value and work needed to restore it. Once again, Gary Reeves provided schematic diagrams from his laptop and printer.

Some personal notes - my first view of a TV picture was the face of a Pilot Radio 3 inch TV set in 1948. It was indistinguishable from magic!! It is my brother, Mark, who submitted the Theremin article featured on the cover of ARC. I remember that FM radios had capacitors installed on the heater connections for the same reason as in Jonathans TV. Sometimes a capacitor would short out and keep one or more tubes from lighting up, thus burning out another tube because of the increased voltage on the rest of the string. This led to burning out still more tubes when people checked them and replaced the "bad" one. A fun problem to troubleshoot!