On Friday, 5 January 2018 16:31:22 UTC, Terry Schwartz wrote:
Ok, a quick google search reveals that the CRT specific rejuvenators apply a high potential between the cathode and G1. The resulting arcing exposes some "fresh" cathode surface. I'd have to believe the area would be tiny and therefore the fix very temporary. Seems like it would also be prone to throwing cathode debris at the phosphor surface, aperture mask, or gun aperture. Ugh. But now I understand the ZAP reference.

Temporary, yes. Typically the customer would get a few more months service then it became unusable due to smearing as the emission declined.

Throwing crud about didn't matter unless it created a short, which it could..

Some folk think it cleaned a bit of cathode, some thing it created electrode hotspots that scavenged gas.

I didn't like zapping at all, preferring an extra turn on the loptf heater wind. That gave a much better lasting result and didn't kill tubes.


I was familiar with the older method that used general purpose tube testers with CRT adapters. There was no such capability with those that I was aware of -- only raising the filament voltage to overheat the cathode and boil up the emitting surface. Seems like a better chance of lasting results, if the filament survives the process.

Funny because I owned a B&K 467 for a while, but I don't think I ever tried to use it for rejuvenation.

The worst CRT I ever did had no visible emission at all, and the tube type, sony trinitron, was known for not responding to attempts to improve emission. I gave it a large permanent heater boost after which it had plenty of emission all round. But colour tracking was lousy, although it gave a nice white the intermediate colours didn't match a healthy set at all well. That thing stayed in service many years and kept going. Occasionally it would arc over for a moment, causing green output to go way up for a few minutes then calm down. It was very much an experiment in trying to fix unfixable tubes.


NT