[Milsurplus] Pre-WWII Aircraft Radio Transmitters

[Ray Fantini]

More on the primitive GO series, the pre 7 GO transmitters used two 860 (VT-17) tubes in a MOPA circuit and  that tetrode was introduced  in March of 1929, a oscillator PA type transmitter of that era (1930-33) would be inherently unstable and produce little power at frequencies above 20 MHz. In a MOPA circuit every tuning adjustment can have an effect on stability and frequency. In the early thirties it was difficult to determine power or frequency above 20 MHz, no less produce a working reliable design that can be bolted into an aircraft. I can see the older series GO transmitters working great up to 9 or 12 MHz  but 25 or 26 MHz another thing entirely. The GO-7 and above used three tubes, a oscillator, driver to decouple the oscillator from the PA and a 803 PA Way more stable design but still subject to instability from shock and vibration. I will still stand by my earlier statement that the PA of the primitive GO series was capable of being configured as a doublers or maybe Tripler to have the transmitter be able to operate the oscillator at a lower frequency with improved stability with the LO set to 5.25 MHz and the output tank tuned to 21.0 MHz you’ll get something on 21.0 and a lot of stuff on 10.5 too, all reasons to support a radical redesign as evidence by the apparent difference in GO-7 and above transmitters. Need a schematic to answer that question.
Ray F