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Quick question about heater voltage
Quick question about heater voltage
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Old 29th July 2015, 12:21 AM   #1
Illinest is offline Illinest
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Default Quick question about heater voltage

I suspect that I might have used 12v on a pair of 6l6 tubes. How likely is it that I damaged the tubes?
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Old 29th July 2015, 12:34 AM   #2
kward is offline kward  United States
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Not likely at all if the 6L6 tube filaments were connected in series so each tube filament saw half of the 12V supply. Otherwise, if they were connected in parallel where each filament saw the full 12V, then I suppose there could be damage depending on how long you left it that way before you noticed it. At least, I accidentally did that once and the tube was fine (caught it in 3 to 4 seconds though).

You could put an ohm meter on pins 2 and 7 and see if the filament is open or not.
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Old 29th July 2015, 12:43 AM   #3
Illinest is offline Illinest
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Quote:
Originally Posted by kward View Post
Not likely at all if the 6L6 tube filaments were connected in series so each tube filament saw half of the 12V supply. Otherwise, if they were connected in parallel where each filament saw the full 12V, then I suppose there could be damage depending on how long you left it that way before you noticed it. At least, I accidentally did that once and the tube was fine (caught it in 3 to 4 seconds though).

You could put an ohm meter on pins 2 and 7 and see if the filament is open or not.

I didn't even think about ohming it out. Brilliant! What would you expect for a reading?

I'm afraid I had it on for quite a bit longer than 3 seconds. Worst case, I'm out the cost of two tubes. No big deal.
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Old 29th July 2015, 12:59 AM   #4
kward is offline kward  United States
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I'd expect something very low in the single digits. Really you're looking for an open circuit or not.
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Old 29th July 2015, 01:07 AM   #5
Illinest is offline Illinest
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Yeah but sometimes you get a reading like 72 and then I don't know what it means.
I would've guessed single digits, but I don't like to assume. Thanks.
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Old 29th July 2015, 01:17 AM   #6
AllenB is offline AllenB  Australia
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Quick question about heater voltage
When you measure it cold, assume there should be a resistance that would give around four times the rated hot current.

As kward has suggested the chances are that it will either be correct or open.
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Old 29th July 2015, 01:49 AM   #7
Illinest is offline Illinest
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I got 1.6 on each of the 6l6 tubes and 5/10 on the 12ax7. Seems about right.
Thanks guys.
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Old 29th July 2015, 03:39 AM   #8
HollowState is offline HollowState  United States
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Filament continuity is not the only concern. Most likely it will survive. It's what (if anything) has happened to the cathode's emission capability from the extreme increase in surface temperature. The prudent thing to do is test it on a good tube tester. Then do a life test by lowering the filament voltage by ten percent and watch what happens to the emission and see if it falls off by much. Allow time for the temperature to stabilize.
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Last edited by HollowState; 29th July 2015 at 03:55 AM.
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Old 29th July 2015, 09:17 AM   #9
DF96 is offline DF96  England
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Short-term over-temperature could improve emission. Long-term could destroy it.
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