KT-150 Tubes- Push Farther or Replace?

Those old emission tube testers aren't going to tell you much about how your KT150 (or really any tube) are doing. A MaxiMatcher and MaxiPreamp can be pretty useful tools ($830 + $990), but if you only have a quad of KT150 and 6H30 to worry about (the latter typically being very reliable), it's more cost effective to just keep track of the hours (check bias periodically) and replace when prescribed. 

A small inexpensive tester is still good to have. Better than none. I think, if you have tubes, it is ridiculous not to have a simple inexpensive one. You leave yourself in the dark.

They test for shorts and tell you, bad, weak, strong, and you can check new matched sets you buy; old ones people give you; stuff you get at garage sales; your existing ones.

Problem shows up, tubes test good, you know to look and find other problems, a bad connection, bad ....

I check all of mine yearly before thanksgiving.

I have a big fancy heavy Hickock or Jackson downstairs. The little 157 and the big one always agreed about shorts and tube strength, so I use the smaller/portable one.

Way back when, when I inherited my Uncle’s Fisher President II: Master Control Panel; FM Tuner; AM Tuner; Viking Tape Deck; Garard Changer; Pair of Mono Amps, Preamps added to the Turntable for MM; Multipath added for Stereo FM: I used to stand in line at the electronic stores until my feet and back hurt, people lined up behind me. When I got my 157, I checked them all at the store, then compared the 157. It agreed with the store’s monster.

Just the basics is confirmation they are not shot, or, they are shot.

My Cayin has 6sl7s and 6sn7s. Same size/look. I switched an L for an N by error, fine for a while: lost a channel, nothing obvious, found the blown tube right away. Without a tester, I would not have found my mistake.

The only thing those emissions testers are good for is maybe telling you if a tube is shorted or dead, the rest of those readings on those types of testers are very suspect.

invalid.

I'm saying, let go of perfection, go for basic knowledge, I think most people will NOT spend for a big/better one.

IF it just finds shorts, not knowing and continuing using them can be quite harmful to your transformer, amp, 

If they appear to work, like an inexpensive sound meter: they do not need to be accurately calibrated. They will be relatively accurate regarding strength as well as find shorts.

If meter shows bad or weak, even if off a bit, relace them, and test the new ones. the results tell you about your tester, and if they are ’matched’ the meter, if not calibrated, will still show you if they are closely matched.

Better than being helpless, in the dark.

@elliottbnewcombjr

We’re saying it’s not good data from those testers. OP sees a pair of KT tubes not holding bias in his amp, and knows the hours are in excess of 2000 - and that alone is far better quality data than an emissions tester will tell you. It’s not adding any information, and in fact might make one draw the wrong conclusions (i.e. that a bad tube is still good).

If you buy a grab bag of old unknown tubes and want to quickly screen out the dead-dead ones - then that’s maybe a use case for these testers.

A tester is not going to predict an oncoming short. Nothing can. Staying within tube usage guidelines and being an attentive user (check bias occasionally) is how you reduce the chances. If it happens, you can only hope the amp's protection circuitry kicks in in time to prevent board damage.