CRT rejuvenation (was: Re: [TekScopes] 577 D2 question(s))


Brad Thompson
 

- wrote on 5/6/2021 7:44 PM:

The TV CRT rejuvenators simply place an excessive voltage on the filament
in the hope it will burn some of the "glaze?" that have built up on the
cathode and that that will increase the electron emissions from the
cathode.
Hello--

IIRC, when a TV CRT ages, the electron emission of a small circular spot on its cathode decreases.
Boosting the heater voltage heats a larger ring-shaped area, leaving the semi-dead spot in the middle.
Since the electron emission then takes place from a ring-shaped area, the onscreen image's focus is no
longer as sharp as it was.

I dimly recall (pun intended) servicing a console  black-and-white TV which had a very dim screen and *three* boosters
connected in series. The set's frugal owner reluctantly agreed to getting a rebuilt CRT installed.

73--

Brad  AA1IP


greenboxmaven
 

You are correct about a rejuvinated B&W jug not being as sharp. A dot triad color jug was affected even more because so much of the beam hit the shadow mask intead of going on through. The rejuvinated gun(s) could look good on the emission test, but the picture was not improved and could even be degraded from what it was before. A slot mask jug got brighter but not sharper. Sony Trinitrons  did not take rejuvination well at all, when they faded it was pretty much curtains for them. The Tektronix 650 picture monitor used a Trinitron  and was quite popular here. There were many efforts to zap them back to good brightness, but very few succeeded.

  Bruce Gentry, KA2IVY


IIRC, when a TV CRT ages, the electron emission of a small circular spot on its cathode decreases.
Boosting the heater voltage heats a larger ring-shaped area, leaving the semi-dead spot in the middle.
Since the electron emission then takes place from a ring-shaped area, the onscreen image's focus is no
longer as sharp as it was.

I dimly recall (pun intended) servicing a console  black-and-white TV which had a very dim screen and *three* boosters
connected in series. The set's frugal owner reluctantly agreed to getting a rebuilt CRT installed.

73--

Brad  AA1IP