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Old 19th July 2008, 08:06 PM   #1
bigwill is offline bigwill  United Kingdom
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Unhappy Briefly subjected heaters to about 12v by accident.

Title says it all. Was testing out my heater wiring and plugged in a set of tubes and had my DC power supply set way higher than I thought. Hearing the 'dink' as the current meter was pinned quickly made me turn it off. I guess they had this voltage for about 5 seconds. The heaters still work fine after this. These weren't valuable valves but they are ones I want.

Is doing this once really anything to worry about?
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Old 19th July 2008, 09:34 PM   #2
Colt45 is offline Colt45  Serbia
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They'll be fine... maybe the lifespan will be shortened by some small amount.
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Old 20th July 2008, 02:31 PM   #3
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Hey I've actually tested some tubes at much higher voltage than that - for, believe it or not, neato night lights.

All the tubes I tested could handle the 6v to 12v jump on the heater. No 6V heater failed until at least 24V and some ran at my max test voltage of 48V for an extended time - to the point I just said, hey... it's good.

The goal of course was to see if I could run some old worn out tubes at 12 to 24v and use them for some interesting lighting. Which seems to be feasible... so I wouldn't worry about a 5 second blip... they should be fine.
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Old 20th July 2008, 06:18 PM   #4
Jeb-D. is offline Jeb-D.  United States
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They should be fine. I've done the same (was supposed to wire in series but did parallel by habit). They were actually left that way for a short listening session, until I realized they were glowing much brighter than normal. After re-wiring it properly the tubes still went on to live a long life.

The filaments resistance is lowest when first fired up and given that the filament was optimized for half the voltage. That explains why the meter was maxed.
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Old 20th July 2008, 10:12 PM   #5
bigwill is offline bigwill  United Kingdom
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Thanks for putting my mind at ease guys
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Old 20th July 2008, 10:27 PM   #6
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If I remember correctly, that's how they used to rejuvinate crt's.

Bring them up to normal operating temp, and then zap the filament with a higher voltage to burn the junk off the cathode. It worked on most, burned some out, and caused shorts on a couple when I was learning how to fix telly's in school.

I can also remember CRT brightners which boosted the filament voltage by about 1 volt.
Give a man a fish and he'll eat for a day. Teach him to fish, and he'll sit in a boat all day long drinking beer.
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Old 20th July 2008, 11:38 PM   #7
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They also used to do this with tubes that showed excessive grid current. I've done this myself and found that it does, sometimes (not always) work.

The theory says that tubes which have run at high anode currents for a long time can get some of the cathode material boil off and stick to the grid. The grid therefore starts emitting and you get high grid current. Giving the tube a 10 to 20 second burst at double heater voltage can occassionally burn it off.

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