Boiling off excessive cathode electrons. CRT heaters electron gun considerations & glass insulative properties to heat! some repro flybacks to blame.

arcadecup

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Check your heater voltages if you're concerned about the cathode life span in your tube. The nominal 6.3ac heater voltage is what most of our monitors are set to be at in spec. By raising it just 10% above specification this increases the rate of depletion by approximately 50%! The extra cathode loading also puts the load higher than normal causing additional stress. Use a fast AC multimeter however it's really best to use an oscilloscope to get the heater pulse reading. Most heaters are ac some are dc. Here is an example of a medium rez heater which would be in a good spec range a bit lower than 6.3... Nominal would be closer to 24pk-pk or 6.3ac rms... There are a handful that run at a lower heater and certain ones that we normally don't deal with at 12vdc. I have seeing repro 3rd party flybacks outputting way to much heater I have seen outputs of 6.8 and sometimes other things out of spec like extra video b+ which gets burned off on resistors.

Most heater voltages can be tweaked with resistors typically in line right before it hits the heater neck pin if needed.

In addition to this more heat would be expected around the neck area. That extra heat now combined with the yoke heat begins to reduce the glass insulating properties. Most glass should remain below 90°C. If it reaches above 100°C there is a risk of arcing from the anode potential to the monitors yoke windings eventually eroding the varnish away from the yoke and glass punching holes in either. After 120°C the glass will lose most of its insulative characteristics and that random tick-tick sound may be the symptom of that or other glass tube wear.

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What specific reproduction flybacks should we be concerned with?

I would suspect that most collectors don't even own an oscilloscope.
 
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But they should! It's a basic tool and they are cheap and plentiful to buy.
But even if I owned one, I would still need to learn how to use it.

And if even if I learned, it wouldn't do me much good because I either use a repro flyback and roll the dice to have a working monitor.

Or don't ever have a working monitor for fear that a rerpo flyback is taking years of the life of the tube. Damned if you do and damned if you don't.

Really only matters if we know exactly what flybacks are susceptible to this issue.
 
I am seeing it specifically bad on circulating k7000 flys and k7500/74000 ..

best to keep the oem originals in if its working without issue for any model.

There are also ways to patch minor case leaking on the focus / g2 divider correctly and clean looking . takes awhile to build it up.
 
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