I am not sure what this is. It was on the 6AU4GTA tube and it connects an 80M 3k volt capacitor from pin 3 to 5. Cathode to the plate.

It seemed to affect the brightness when it was removed from the tube. I removed it because after an hour of running it was melting (as seen in the photos).

It's a ceramic cap, typically around 68 to 100 pf. It increases sweep width slightly (and reduces HV concomitantly).

Ditto...It probably started melting from the cap leaking current or the plastic dielectric breaking down.

If width is good leave it off, and if bad maybe find a new cap of similar value and solder the new cap in under chassis.

Late 60s onwards Zeniths and some other sets had this gimmick built in and switchable so one could get more life out of H output tubes.

It's a ceramic cap, typically around 68 to 100 pf. It increases sweep width slightly (and reduces HV concomitantly).

Here I thought I had a reasonable vocabulary, but that word is a dandy! The way it reduces HV. I had a good idea of what it meant, but looked it up anyway. :scratch2:

Ditto...It probably started melting from the cap leaking current or the plastic dielectric breaking down.

If width is good leave it off, and if bad maybe find a new cap of similar value and solder the new cap in under chassis.

Late 60s onwards Zeniths and some other sets had this gimmick built in and switchable so one could get more life out of H output tubes.
The early B/W sets had the large tapped resistor in the H/V cage that had a bearing on the width and linearity. It shunted the damper tube.

...The way it reduces HV. I had a good idea of what it meant, but looked it up anyway. :scratch2:
Yeah, the width cap is a 'no free lunch' sorta deal. Much beyond 100 pf, the HV gets too low. 'Concomitantly' is a hillbilly way of sounding geeky.:tongue:

Thanks, everyone for your quick replies. I have ordered a new old stock 6AU4GTA tube and we see how the width is.

The first pic looks like an artist's rendering of a burnt alien skull.

lol