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The AO-100 was TMC's equivalent of Collins' PTO. It provided near-linear tuning over a range of 2-4 Mc and lived inside an oven, in order to achieve stability on the order of about 20 ppm. The AO-100 was designed, at least in part, by Les Norde, later the chief engineer at Hammarlund, in 1952-53. It was used in a variety of "VFO" applications, including in the VOX, the RTF unit in the GPT-750, the CMO, the PMO (a sort of "lightweight" version of the VOX), and others. It was manufactured at least into the 80's (I have interviewed a former TMC-er who was performing the extremely time- and labor-consuming calibration procedure on AO-100's in 1982).
Electrically, the AO-100 is 6AB4 triode Colpitts oscillator and half of a 12AU7 cathode follower. The unit also contains a 100Kc reference oscillator that uses the other half of the 12AU7. See the VOX-5 manual for details, for example. The tuning knob drives C301, the large tuning capacitor visible in the rear view. As the capacitor turns, it also rotates a cam that drives a second capacitor, and this mechanism removes the non-linearity inherent in a tuning mechanism that uses a linearly varying tuning capacitor (since the resonant frequency varies as 1/C1/2).
If you are lucky enough to have one of TMC's various frequency-generating devices (VOX, PMO, GPT-750, or whatever), your AO-100 is probably badly in need of service. A good cleaning and re-lube will almost always bring it back to correct operation, even after 60 years of service. It's linearity is likely to be completely acceptable, so you won't need to do the very tedious job of adjusting the linearity cam--a nearly lost art. See Jay Spivak's excellent writeup on GPT-750 Master Oscillator Repair.
|5910.21-7. AO-100 bottom view.||896.17-6. AO-100 rear oblique view.||5910.21-6 AO-100 rear view.|