Color crt life

[timmy]

Is there any such thing as keeping color level or even brightness level down to prolong the life of a 21fb or fj crt. Or even lower heater voltage.

[zeno]

In theory running thing down will give longer life to most of the set.
A muffin fan would help even more IMHO.
Now this will start a food fight but I was always a bomb tosser so hear goes.
The longest lasting CRT's were Zeniths from the 70's. The longest of
those were in sets with instant on ! ( flat chassis & CC2 ).
So keeping the CRT filament ( only ) warm probable is a plus. It eliminates the
hot / cold cycle, a bad thing in electronics.

73 Zeno
LFOD !

[timmy]

Originally Posted by zeno

In theory running thing down will give longer life to most of the set.
A muffin fan would help even more IMHO.
Now this will start a food fight but I was always a bomb tosser so hear goes.
The longest lasting CRT's were Zeniths from the 70's. The longest of
those were in sets with instant on ! ( flat chassis & CC2 ).
So keeping the CRT filament ( only ) warm probable is a plus. It eliminates the
hot / cold cycle, a bad thing in electronics.

73 Zeno
LFOD !

Now that’s odd I always thought instant on beat up a crt never shutting off but if stats say otherwise then ok.

[Electronic M]

I think the instant on is only beneficial for regular use sets. If it's not on every day or more than once a week it's probably not going to help any more than say variacing a TV every power up. Cathode poisoning can occur if a tube heater is on for a pronged period with no emissions. Ask vacuum tube computer engineers.
But it probably is beneficial for a daily use TV.

[old_tv_nut]

Originally Posted by timmy

Now that’s odd I always thought instant on beat up a crt never shutting off but if stats say otherwise then ok.

I think the good CRT life cited was because they were good CRTs, period. The instant-on probably shortened the life, not lengthened it, but even then they were still good. Hot/cold cycling doesn't reduce cathode life as far as I know; I think it would only help reduce filament failure due to mechanical stress, which I believe was an almost non-existent problem to begin with. Every opinion I ever heard in the labs at Motorola and Zenith was that instant-on shortened CRT life.

[old_tv_nut]

Originally Posted by timmy

Is there any such thing as keeping color level or even brightness level down to prolong the life of a 21fb or fj crt. Or even lower heater voltage.

A CRT (or any tube) is in wear-out mode from the first time it's turned on. Reducing beam current definitely extends the life of a CRT, but in an odd way compared to amplifier and diode tubes.

CRTs draw current from a variable area of the cathode depending on the amount of beam current. That's why the spot size is bigger in the highlights, and why the beam current vs. g1-cathode voltage follows a power law (gamma) about 2.5 rather than the theoretical value of 1.5 for an amplifier tube with more uniform current over the whole cathode. So, even though you extend the life of the CRT by running lower beam current, eventually the cathode center area will wear, you will have to turn up the drive to get the same brightness, and current will be drawn from a larger area, increasing spot diameter ("blooming") as the tube wears out.

So, if you can live with a dimmer picture, you will get longer life and smaller spot size (better focus).

[Jeffhs]

My grandmother bought a 25" Sears Silvertone color TV when she retired in 1969. The set worked very well, and kept working about a year or so (again, very well) with its original CRT after she died in the early 1980s, IIRC. The TV didn't see that much use, as my grandmother only watched the evening news and sports most of the time; however, she did watch reruns of the TV series MASH for several years before her death, but she didn't watch anything else (except one or two very early morning moon landings). This is probably, even likely, why the TV's CRT lasted as long as the set itself did. If her set had been in more or less constant use (it wasn't, as my grandmother lived alone and, as I mentioned, she did not watch much TV at all except the news and MASH) the tube probably would have died within perhaps a year or so.

[timmy]

So basically by lowering the color to the screen itself would be beneficial to extending the life of the crt.

[Pio1980]

My nonprofessional unscientific observations were that substantially less then maxed out brightness level combined with using the set only for actual active viewing of selected programs vs leaving it on most of the time maxed out for daytime open curtains was a difference of ca 15-25 yrs vs ca 5 yrs service from a color CRT.
So, yes, reducing brightness plus not leaving it on for hours of background noise or as a burglar diversion lamp should extend usable service.
One other impression was that most of the "younger" CRT aging was with NAP group sets.

[timmy]

Well since no one is rebuilding any 21fb or fj or any other crts we have to do whatever may help prolong the life of these tubes. Once gone there gone forever.

[Alex KL-1]

+1 for voting about using at moderate brightness and color.
Or using at little less than maximum settings, but only for demonstrations.
Or maybe watching low bright programs like terror/horror movies (well, is easier with gamming).
I know that if one operates the CRT always below its maximum ratings, and with proper adjusted bright/contrast/color for most correct picture (considering the set in question) will results in a good life.

Make sure to measure the line voltage when using, avoiding using when is much higher than it's design (or reduce with a trafo or variac).

I believe that with such simple measures, will be a long life.

A extreme option is to make a "soft start" for the filament, to avoid the inrush current when powering on, but is not a common failure for a good CRT.

[JohnCT]

Regarding filament - yes, running at lower filament will extend life much the same as running lower brightness and contrast levels - lower beam current.

I discovered by simple observation that some RCA XL100s were having premature CRT failures about the 5 year mark. Not really bad, just soft. These chassis had a two position switch on the back for line voltage, and the filament in these sets were line AC sourced, not the flyback, so there was no regulation involved. The examples with weak tubes always had the switch in the low position (which would raise the filament). I don't recall if I the filament was above 6.3 nominal in the weak examples or below 6.3 in the examples that had long tube life. That was a long time ago..

Back in the late 70s, I was young, full of beans, and any little thing that would pop in my head would often become reality.

I had a 19" Zenith, and I built a small add-on circuit to the filament supply to the tube that lowered the filament voltage to the tube after it was running about 10 minutes. I did this with just a relay, 10W resistor, and a transistor/capacitor relay driver.

The tube was perfect the whole time I had it, but as someone commented earlier, these tubes were ridiculously long lived anyway, so who knows if it had any effect.

John