More playing with crt's, this time dg7 32 vinatge scope tube

[dr pepper]

I have a old 'scope tube as per the thread title.

I have connected it up to a power supply to see if I can get a dot before going further.

The voltages for the best dot are as follows:

Kathode -200v
g1 -245v
g3 -180v
anode 290v
heater 6.3vdc

All deflection plates shorted and connected to the anode.

The brightness control does very little, the focus control does work and has a 'best point', but the smallest I can get the dot is 3mm or so.
I have 2 tubes and they are the same, not new salvaged.
I'm thinking maybe the cathode isnt negative enough.

 

[dr pepper]

Sussed it.
Voltages were correct, it wasnt the volts it was the lack of smoothing.
I paid the price for parts mining, turns out my negative supply cap was high resistance, my esr meter didnt even show a reading.
I temporarily shoved a photo flash cap in there and I can now get the dot down to less than a pinhead.