So
First observation is no glow in the neck (can be hard to see, but I can see it fine on the working one), but that I have 24KV under the cap, so flybacks occuring.
Managed to trace the Tubes model number (AT12A9SLB22) to a website listing adapters to fit to a tube regenerator. Tracing adapter A8 gave me the following neck pinout for Base type
B10-277
Then with much searching (amazing how hard it is to find CRT info) to a pinout of
5 G1
6 Green K
7 G2
8 Red K
9 Heater 2
10 Heater 1
11 Blue K
12 G4
So heater checked and loop resistance is fine.
Checking on the flyback transformer 334P0311 gives me a HR 46097 and the circuit diagram checked against the pins, getting a 20V peak waveform on the heater supply pin 5. Loop checked to the neck socket and seems ok but a small resistance. Gave everything a clean and reassembled.
Got the glow back
Turned up brightness and the first 1/3rd of the picture is stretched, then a bright line, then a wibbly but otherwise normal picture.
While its not mine, it appears exactly like this one
Everyone that I have researched has then just done a capacitor replacement, mainly C418, so without a circuit diagram, I am forced into almost random 'recapping' (ooh I hate that phrase). At least it will keep me busy.
