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Antique Radio Technical Forum
Tubes That Test High

Posted by Bob Masse on 04/05/2009 21:11

::Tubes that have gas will also read high, have you tested for gas?
::Dave------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- : Hi! Yes I tested for gas and it past the test. What happened was I bought a batch of about 500 tubes and found that when I tested groups of a number occasionally there would be one tube in a group that pegged the meter on a Hickok 600A. So I would test them on a Precision 10-20 usually with the same result. I found that if I moved the bias and the english about 3 markings from the specs. on the 600A tube tester I could get the tube to read on scale. So I'm thinking it might just be tubes that need some burn in time. I did find 2 gassed tubes in the lot and for some reason they make the meter read backward on the 600A, so I reversed the meter switch and tested. I was amazed by the purple glow and that the meter went to about half way up the scale.Thanks for your replies. Bob Masse -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------:Hi! Again, I just found the answer to my question. Here's what it says in the precision 10-20 manual. "It is not uncommon for a tube manufacturer to make a change in a particular tube's specifications.This change may,however,indicate itself on the Precision Electronamic Master and necessitate a new test limit for that particular type number.Therefore, should a particular type number be found to vary consistently from the assigned average roller chart limits, merely redetermine the new Control "D" average setting required to pass these tubes at approx. 70 (on the 100 scale) of the green GOOD sector and record same reference with respect to that manufacturer. It can readily be seen that a consistently low or high reading for any particular tube type of a definite manufacturer is not to be taken as indicative of a poorer or better run of tubes nor as a defect in the tube tester." So not only the tube manufacturer but the year the tube was built or the batch run could affect how a tube reads on a particular tester. I think this can apply to all tube testers but the formula for redetermining the settings might be higher than 70% of scale.Hope this helps anyone who was having the same problem. Bob Masse

Tubes That Test High 
Bob Masse 04/05/2009 11:40 
Thomas Dermody 04/05/2009 14:31 
easyrider8 04/05/2009 18:22 
Bob Masse 04/05/2009 18:53 
Bob Masse 04/05/2009 21:11 
Thomas Dermody 04/05/2009 23:13 
It's All Relative 04/06/2009 00:05 
easyrider8 04/06/2009 02:27 
Why Bother? 04/06/2009 12:54 

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