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hi, all, need help on this one, i was testing some tubes last night and left the house for 4 hours. when i came back i realized that i had left tester on with the tube still inside the tester socket. Naturally, i finished testing the tube and then unpluged it. I then found out the needle pointer in the meter would not return fully to the left (10 o'clock position). I plug it back and hoping that i could adjust it with the lind adjustment knob. Didn't work and still would not return fully to the left. Please help, what's the problem could it be fix. thanks
-ray-
Follow Ups:
Tonight, before i plug the tester in again, i noticed that the pointer is only slightly off as compared to last night. I then manually adjusted the pointer with the adjusting screw. I went ahead and test some tubes that i known and it gives accurate reading like previously. After i finish, i unplug and noticed the pointer is now resting past the most left position (beyond the left range mark). i then again adjust the pointer with the adjusting screw and retest the tubes again. Everything works fine from here on and when unplug the pointer is resting perfect on the left starting line. So now is everything is fine and dandy. i guess it's like Chris H is saying that there may be static build up when the tester is on for a long period of time. When static is gone, unit is back to normal ! It's one of those weird happening.Chris O, i don't think the meter is magnetized since it give the same reading now as it did before with the known tubes. But it's a good thought though, thanks.
Plastic meters on tube testers can take a static charge just by running your finger across them. It is a common problem in the winter. The charge on some meters can be so severe that the needle will stick at nearly half-scale. The anti-static cleaner really helps, but it's best to avoid touching the meter with anything. I would doubt that just leaving the machine on would charge the meter-- more likely something rubbed against it--like the cuff of a shirt.
If you just left the tester on with a tube in it, only the filament current should have remained on while you were away. With most testers, plate current is not flowing until the merit or quality test button is depressed. You may have a static charge on the plastic meter face. Such a charge will cause the meter to act strangely. Usually a plastic anti-static cleaner, like Endust for Electronics, will help. This type of problem rears its head when the heating season starts and the relative humidity in our houses goes down. The meter zero adjustment is a mechanical one, but this is not likely to have changed.
If the meter was active (deflected) during that time, you could have magnatized the meter if it was not desigend for continuous service. Does the meter give similar readings now as it did before the problem when testing a known tube?
Usually "fully to the left" is a mechanical adjustment via a screw on the front of the meter.
But one other issue: Some tube testers will not supply large filament currents for long periods of time. For example 5U4 with it's 3 Amps of current may cause damage to the tester's power transformer if left on for more than a few minutes.
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