Dynaco lore - TC-3X - The PAS-3 to PAS-3X tone control modification manual ...

Bob, this is interesting. Was it simply a circuit redesign using different components, that when centered, were more "approximately flat", i.e. flatter than before, in other words not a true "tone bypass" circuit? Or, were they some kind of special pot that electrically and completely removed themselves from the circuit like a modern tone bypass switch? Were they detented at the center?

The conversion kit made the PAS-3 or PAS-2 the electronic equivalent of the PAS-3x and PAS-2x. Those were special tone controls that provided true out-of circuit operation of the frequency-contouring tone control circuitry (take a look at the schematics of the original PAS vs. the "x" versions to see what Dynaco did).

Note that Bob states that his kit consisted of several new parts...but no new knobs. The old PAS-3x and PAS-2x had splined shafts on the tone controls, and splined knobs to match. New PAX-3x and PAS-2x had setscrew knobs that went onto plain shafts. So the controls supplied with the TC-3x modification kit must have been different from the ones supplied with new-construction PAS-3x/2x kits, in that the shafts were different though the guts were the same!

At least that is how I would interpret the data. I worked in the service department of a Dynaco dealer in the early 1970s; the TC-3x kit was available by special order only and I only saw one come through the shop, ordered for a customer; but didn't study it carefully. My own Dyna PAS, which is modified with Van Alstine Super PAS Three circuitry interfaced with tone controls, has the non-splined shafts and knobs and thus was born a new-construction PAS-2x (I have retained the original brass front panel).