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Old 3rd January 2004, 02:17 PM   #1
Tensop is offline Tensop  Lebanon
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Default A question regarding Valve fillaments..

Hi guys.. i couldent really find a forum on here thats more adequate than this one.. so here goes

I recently had the fillament supply circuitry die on my monitor. and ive bypassed it, and supplied it with its own 6.3v.. but may i ask, is it safe?

At times the Monitor will be off, but the fillament will still be receiving power.. and in some occasions the monitor will be on but the fillament wont be. Also.. what kind of power draw am i looking at for a fillament? i'm supplying power to it with an lm317 and a 1000uF capacitor.


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Old 3rd January 2004, 07:01 PM   #2
dhaen is offline dhaen  Europe
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The current for a colour CRT should not exceed 1A, so you're safe there.
Caveats:
The Heaters are isolated from the cathode material with a fine insulation sleeve. It's important not to exceed the breakdown voltage. It's best to follow the monitor manufacturers practice, and set the heater voltage elevation to a reference level. This can be 0v (chassis), or to some voltage between 0v and 100v. You should be able to measure the original setup. Of course if it's elevated, you must take care to insulate your external power supply.

The heater operating voltage of quick-start types is critical. 5% error can half the CRT life. Not all Japanese CRT's had 6.3v heaters. Some (Mitsubishi) made lots with 6v heaters. If I didn't know for sure, I'd set it mid way.

Running the heaters with no beam current is inadvisable.

Running the monitor with no heaters could lead to EHT (HV) breakdown.
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Old 4th January 2004, 05:26 AM   #3
Tensop is offline Tensop  Lebanon
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Thanks for the advice.

According to a service manual on a monitor with an identical tube(however non identical to the actual monitor chassis) it is supposed to be receiving 6.3v.

I might modify the power supply i am using so it has a soft start.
eg: 4 seconds to reach 3v, 2 seconds to reach 5, 1 second to reach 6.3 that should reduce any thermal stress. I'll use a relay tapped off the mains switchi inside the monitor so the fillament is always on when the tube is on.
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