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KT120 and KT150 tubes not up to spec [message #84517]

Wed, 08 February 2017 15:27

gofar99
Messages: 1949
Registered: May 2010
Location: Southern Arizona

Illuminati (5th Degree)

Hi everyone one of my worst fears (others no doubt share it) seems to be happening. Tungsol KT120s are red plating well below their rated dissipation. Seems like at 60-70%. Not good for class A amps. KT150s are being received that are just plain defective. A UK licensee of some of my designs has reported the problems starting about 4 months ago and now it is a thread on diyaudio.com (see the link).

http://www.diyaudio.com/forums/tubes-valves/303273-anyone-out-there-kt150.html#post4975833

My suggestion is that if you get any tubes that red plate or just don't seem right...send them back until you get good ones. Maybe the suppliers will get the word and not accept seconds from the factory and QC will improve. There is always hope.

Good Listening
Bruce

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Re: KT120 and KT150 tubes not up to spec [message #84530 is a reply to message #84517]

Thu, 09 February 2017 09:38

Wayne Parham
Messages: 18787
Registered: January 2001

Illuminati (33rd Degree)

I hate this, Bruce. But I feared it might happen too.

I think it's a two-fold problem. One problem is the materials needed. Some aren't as readily available, and are expensive. So I would expect the temptation to substitute for cheaper materials might come into play. And a second problem is modern tube manufacturers aren't as likely to even try to be as concerned with quality as they were decades earlier. Their market is smaller, and I think the companies themselves are smaller. I have a hunch they feel less "visible" and more likely to cut corners.

Tube loving audiophiles will naturally suggest NOS tubes. That's awesome where you can find them. But new equipment manufacturers need to be able to find consistent quality new production tubes. So I'm with you on this: I hope the current tube manufacturers understand that they are visible, and that their products are used by sophisticated customers. They can't slack on quality without losing their place in the market.

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