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Quality Issues With GT 12AX7M Mullard "Clones"

Posted by Jim McShane (D) on December 8, 2006 at 15:55:53

This week I got my first small shipment of GT 12AX7M Mullard "clones" since GT had their "stop sale" on them a few months ago. If you don't recall, they sent a whole shipment back to China due to quality problems. I don't know all the findings, but they did say the tube pin protector was sometimes the cause of small cracks in the base glass (rendering the getter white and tube useless). FYI, the new stock has no pin protectors.

I tested the new fresh GTs today. It was not a fun experience - not pretty, not good at all. 11 of 14 tubes are rejects. The tubes came out of the box with bent and mangled pins, as if they were pulls. Also, many of the pins had a lot of whitish-green corrosion deposits on them. In fact on some tubes the glass base had a greenish cast to it, apparently from the reflection/refraction of corrosion on the pins where they pass through the glass. This piqued my curiousity, so I examined the tubes carefully under a strong light with a magnifier. In some tubes I could see internal copper pin wire that appeared to be corroded too!

The pins are also very rough and ragged, the pin surface is full of rough, uneven areas. The contact from pin to socket in my testers was so bad I had to scrub the pins and straighten them just to test the tubes!

The tubes are also VERY sensitive to any AC fields near them, they hum at the drop of a hat.

Some triode sections tested quite low for Gm too.

I rejected 11 of the 14 tubes I got in (roughly 77%). Now 14 tubes is not a huge sample, but the problems I saw were common to many of the tubes. Based on my experience it would lead me to believe there are many other tubes in similar condition out there.

At this time I've decided not to carry the tubes (after the 3 good ones are gone that's it). The supply is still just trickling in, so many vendors don't have any as yet. But if you do go in search of them - buyer beware!

It's a real shame, when it's right that tube can sound really good. It's one of the very few new production tubes with a warm-ish tonal balance too.

Finally - just so you know - I was very hesitant to post this, as it seems every time I try to warn people about quality issues I get a lot of hate mail and nasty responses. I hope people reading this will find this useful and not somehow offensive.

This post is made possible by the generous support of people like you and our sponsors:

Schiit Audio

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