Design considerations for Vox choke choice

[Bob M.]

G1,

That's positively right re: what you're saying about current draw through the choke. But since posting my original query, I studied the early Vox schematics a little closer: On the AC 30 and AC 50 amps, the power supply connects to the center tap of the output transformer primary and drives the power tube plates before the choke (like a Fender amp); the screens are connected to the power supply after the choke. Now with the AC 10 and AC 15 both plates and screens are connected after the choke so that's why a larger choke is fitted with more mA capacity.

Another interesting note from the early Vox schematics: the 2x 100R resistors are connected to the plates of the power tubes on the AC 10. The screens are directly connected to the output transformer center tap with no resistor(s). On the 1959 schematic, the AC 15 had the same wiring as the AC 10 (2x 100R resistors connected to the plates) but by the 1960 AC 15 schematic, the 2x 100R resistors moved to their more familiar positions, connected to the screens, with the plates directly connected to the ends of the output transformer primary. The AC 30 always had the 100R screen resistors, schematically speaking.

[g1]

For the amount of sag I think that would introduce, I would suspect the 100R's shown on the plates rather than the screens was a typo.
Perhaps someone with more hands on with the oldest units could confirm one way or the other?

[Bob M.]

g1,

It could be a typo but I suspect that they (Jennings) figured out that the amp worked better, sounded better and was more stable with the 2x 100R resistors on the screens. After all, with alot of early tube guitar amps there are some things that we now would consider to be errors, or maybe less-than-optomised situations implemented but that that eventually got corrected later.

This was a good discussion about the Vox choke and its placement in the filter circuit. I guess with my (contemplated) homebrew I'll try different placements for the choke within the filter circuit and see how it sounds, which of course, is the ultimate arbiter.

Thanks to all who participated in this lively, thoughtful discussion.

Bob M.