[Phlogiston]

Of the 6469 spare tubes I have not one is a 3Q4.

I have made the adaptors for the UX99 and UX120, but I have not tried them yet. I'll probably get to that soon. One of them is set up for the 3S4 - but with 90V going to the screen. This is probably going to work but with some extra screen current which would not be detectable - unless the tube fails.

[Arran]

Russ;
  I think that the 3Q4 must have been another one of those transitional type tubes that was replaced due to electrical code issues, like a 50B5, such as if it were plugged into the wrong socket it would liven something up. I have a lot of 1940s and 50s farm battery sets, and have owned a number of three way portables over the years, I only have one that used a 3Q4. It's a Canadian Marconi model 260 from around 1946-47, and the 3Q4 isn't even in it, it's one of those weird three way portables that developed the voltage for the battery tube filaments by connecting them in series with the cathode of the 50B5 output tube (who's filament was in series with a 35W4 and a dropping resistor), and in AC mode the 3Q4 is switched out of circuit and not used.
Regards
Arran