Lessons Learned

Tubes Asylum

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In Reply to: KT150 puzzle (longish) posted by tlea on August 20, 2024 at 18:42:39:

I'm posting a summary of what I've learned from this experience because some other tube novice might find it informative.

I bought four backup KT150s from a questionable source, at my risk. Had them tested. Three tested strong (current 86%-102%/transconductance 95%-109%) but one tested bad (no output). The tester generously gifted me one KT150 that was serviceable (77%/91%).

I switched those in and had my "1st string" KT150s tested. Three tested strong (80%-86%/87%-93%) but one tested lower (73%/87%). I've shuffled them around and now have the highest testing four running in the amp.

So now I own 9 KT150 tubes: 1 probably bad, 2 OK, and 6 pretty good. I'm beginning to see why you tube guys tend to have so many tubes.

Here are the lessons learned:
The "auto-bias" feature seems like a good, low maintenace concept, but the drawback is that if you don't manually check your tubes occasionally, you can have a dead tube in your amp and not realize it. Who knew ???

There is no option to manually bias with this amp. Supposedly it has a built-in tube testing program that automatically shuts it down if a tube goes bad or biases low, but that didn't happen with the tube that tested "no output". I don't see that as a big deal - after all, it's an amplifier, not a tube tester. But the lesson is: Beware. Unlike solid state, it's not "set it and forget it". Which makes things kind of fun and interesting, IMO.

All of this may seem routine to you experienced tube folks, but it is a big mystery to the rest of us.

. . . in theory, practice and theory are the same; in practice, they are different . . .

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Follow Ups Full Thread

Topic - KT150 puzzle (longish) - tlea 18:42:39 08/20/24 (7)

Lessons Learned - tlea 18:13:03 08/28/24 (0)

RE: KT150 puzzle (longish) - 6bq5 20:13:08 08/20/24 (5)

RE: KT150 puzzle (longish) - Nunki 01:09:10 08/21/24 (4)

RE: KT150 puzzle (longish) - 6bq5 11:05:35 08/21/24 (0)

Surprising - tlea 07:14:22 08/21/24 (2)

RE: Surprising - 6bq5 11:37:22 08/21/24 (0)

You'll need to crank it up a bit! - Ralph 11:12:44 08/21/24 (0)

Follow Ups

Lessons Learned - tlea 18:13:03 08/28/24 (0)

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