Just install under damper tube
It was in the gc catalog gc67

It puts a small capacitance, typically 100 pf or so, between cathode and plate of the damper, to increase sweep width. Old techies used to do this, starting with 68pf, 82, 100, or 120pf. But with each step up, the HV drops proportionately. So there's "no free lunch". Above 120pf, the HV loss is too much.
The caps used were disc ceramic, 4KV rated for BW sets, 6KV for color.

[EDIT.] Hor output cathode current also drops proportionately with each step up, contributing to "no free lunch".

That could be an issues if another tech work on the set later and corrected
The low voltage problem and had too much width not knowing of a mod was done

It wasn't done often, and only in "last resort" cases of insufficient width.

[EDIT.] Hor output cathode current also drops proportionately with each step up, contributing to "no free lunch".

In color sets where the cathode current is excessive and can't be adjusted low enough on top of poor width I think with regards to lowering cathode current "win-win" would be more accurate than "no free lunch"...

In color sets where the cathode current is excessive and can't be adjusted low enough on top of poor width I think with regards to lowering cathode current "win-win" would be more accurate...
But only to a point, where HV regulation falls apart from insufficient power driving the flyback. There were certain 25" Admirals in particular, using 6KD6 and that crazy pulse-feedback HV regulation. Cathode current would spike to over 400 ma. on bright scenes, and we played with G2 voltage and different damper cap values, to get K current within reason consistent with stable regulation and width. We informed the customers of the modding, and told them to holler if it didn't hold up, but it held up OK.

Just install under damper tube
It was in the gc catalog gc67

Yep. I remember these hanging up at the parts store. I think we used them on occasion to limp a couple of old timers across the finish line..

John