Ok - I got scope
It's a cow-orker's Tek he's got on extended loan to me. I think that 15,750hz is 63 microseconds and I can get it in that area - my rough look on the scope was in that range. Being a Tek, I can believe it.
The set is a Sparton 5020something, chassis 26SD160. Folder 13, set 128 Photofact FWIW.
They were crafty on this set, not only does the heater float, it's tied to the cathode on one side anyway. It's a dedicted winding - no surprise there.
I can push it on frequency (or close), or way off either way - no dice. The range of the oscilator is quite something, and I can run it down to around 14khz and up to like 18, at least off the DMM's built in counter. I can look closer with the scope though.
I'm going to see if I can disconnect the dead as a doornail vert section just as a check to see if that's killing things - it looks like a simple wire unhook.
I've got a 6W4 comming but I've got a few 6AX4s laying around I can try now.
There's no sub listed for the flyback, only Sparton part PC70010
I'll try to get my image scanner here shortly so I can scan in schematic clips if needed, too.
I'm not ready to condem the flyback - it doesn't get hot much at all.
Thanks for the advice!