On Thursday, January 4, 2018 at 11:32:37 AM UTC-6, wrote:
On Monday, January 1, 2018 at 10:24:14 PM UTC-5, wrote:

Never do that. I've seen so many CRTs ruined by rejuving. Increasing heater voltage works better and stays good.

Exactly what do you think rejuvenation entails?

Peter Wieck
Melrose Park, PA

Rejuvenation entails *temporarily* running the heater of a tube at a high voltage, the theory being it boils up the thorium from the cathode and exposes fresh surface. It does not entail leaving the filament at a higher voltage in operation.

That was done with so-called CRT "brighteners" which were merely step-up auto-transformers. We've all seen those. They worked, for a while. But they did cause other picture problems, like saturation that made the contrast look eerie. Sometimes you could adjust some of that out.

Any tube tester could be used to "rejuv" a tube or CRT. The process was well known in the shops. The key was always to leave the tube in the tester for some period of time after applying the 2X or 3X heater voltage for a minute or so (hopefully you didn't burn out the heater) and then seeing if the emissions dropped off unacceptably over the next hour. If emissions stayed up, the rejuv "took" and you were good. If not, maybe you sold a new tube.

The problem with CRT rejuvenation was that the excess electron flow eroded the tiny aperture hole in the gun, causing blurry focus, smear, etc, on the face of the CRT. In lots of cases the customer didn't care, he did not want to spring for a new picture tube or new TV.

I often got the job of replacing CRTs after the sets came back in when the rejuvenation didn't hold up, or the customer didn't like the result. I had a knack for doing convergence, which can be one of the most frustrating things to attempt.