KT-150 Tubes- Push Farther or Replace?

@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. 

The problem with some of the cheap emissions testers is they only run the tube at 30 volts, some of the better ones maybe up to 150 volts, the kt150 needs to be tested at a higher voltage. The best way to test them is in circuit. 

@mulveling is a wise man listen to him. Enjoy the music

Agree with @invalid, some circuits are running up to 600V plate voltage at about 80 - 85 mA current per tube. I ran my KT150s in the 50ma range per tube and they still sound great. Some of the diy folks were talking about this a while back, getting up to 4,000 hours without issue, yet noting some of the older tubes had getters fading faster than more recent production past few years. Best to follow the rec above "best way to test is in the circuit". Keep a close eye on this 2nd set for a while and check how quickly they stabilize at their first bias set point. Best of luck.

After a little reading and putting some more thought into this I’m realizing the reality of this (at least my reality!). As @mulveling first suggested- my system uses 4 different makes of tubes. A gang of 8 KT150 and 11 6H30’s. My DAC uses a couple of the smaller 12AT7’s (which seem to go on forever). With this commonality across the equipment I don’t really see myself critiquing individual tubes as opposed to wholesale changeouts when approaching the recommended end of life hours.

It also seems (pointed out by @mulveling ​​​​@invalid) that a tester really isn’t going to buy me much when it comes to the KT150 in particular due to the voltages required for an accurate test/comparison. The test stations equipped to deal with these are of considerable expense (more than a new set of tubes) and in reality I would just pull and replace.

I liked the thought of having one though- kind of nostalgic but (at least in my case) it doesn’t seem like I would put one to much use. As always- I appreciate the advise given!