Testing tubes………………?

[Dr Morbius]

Hi I received an order for a pair of Linlai KT88-D tubes and tested them on my tube tester and my B&K 747b tester showed no shorts and no emission leaks on both but the output test showed 65% on the first tube and 70% on the second. On the tester meter the bad ( red ) section goes from 0% to 55% and the question mark ( white) section goes from 55% to 70% and the good (green) section goes from 70% to 120%. My question is with these tubes being new, if I ran them for 25 to 50 hours or so and break them in, would they show a better rating? Maybe everyone knows the answer but I really am not sure.
Thanks for your advice!

Steve

 

[W9TR]

It might just be that their transconductance is at the low end of the spec range for a KT-88.
How does a known good KT-88 test?

 

[Michaels HiFi]

Hi I received an order for a pair of Linlai KT88-D tubes and tested them on my tube tester and my B&K 747b tester showed no shorts and no emission leaks on both but the output test showed 65% on the first tube and 70% on the second. On the tester meter the bad ( red ) section goes from 0% to 55% and the question mark ( white) section goes from 55% to 70% and the good (green) section goes from 70% to 120%. My question is with these tubes being new, if I ran them for 25 to 50 hours or so and break them in, would they show a better rating? Maybe everyone knows the answer but I really am not sure.
Thanks for your advice!

Steve

Hi Steve - has the tester been calibrated recently so you know it's accurate?

Other observation would be that typically new production tubes (in my experience) are never as "strong" as vintage tubes.

Finally, I would say that is what I have multiple testers - they each test tubes in a slightly different way with different voltages and such, and no one tester is ever 100% accurate.

 

[Dr Morbius]

Tom, thanks for answering and I have 4 more coming Monday………… and Michael, the tester was calibrated 5 months ago and new production tubes not being as strong as NOS tubes is very interesting to say the least…….also what is a good tester that can test type 45 tubes and also KT170 tubes? Or I’m guessing there ain’t no such animal?

 

[Michaels HiFi]

Tom, thanks for answering and I have 4 more coming Monday………… and Michael, the tester was calibrated 5 months ago and new production tubes not being as strong as NOS tubes is very interesting to say the least…….also what is a good tester that can test type 45 tubes and also KT170 tubes? Or I’m guessing there ain’t no such animal?

Before we have you spending more money on a tester, I'd like to make sure your sockets are clean. I know they get dirty to the point where on one tester I received it was completely not working. After gently cleaning the socket it worked wonders.

I sugest this:

1) make sure on any vintage tubes the pins are clean. This 30 second video show you how:

2) Spray QD cleaner onto a pipe cleaner (NOT in the unit). Then while still wet GENTLE clean the sockets.
Pipe cleaner: https://amzn.to/48zDUy5
Spray: https://amzn.to/48DauxE

3) you can buy known test tubes (typically 6L6's) off Ebay from a place called BlueGlow Electronics. They are known tested good tubes that you use as a reference to check the calibration of your tester.

Photo example on this unit about using the pipe cleaner. I also do the dirty cleaning parts on the testers before I refurbish the unit cosmetically. Should your tester be reading low or high this will help you gauge that so that a when a tube tests low you know it may actually be stronger.