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Tube Identification Needed (12AX7... or is it?)

U

UnGrounded

Well-Known Member
So I got this Mytron tube in its original box. It is labeled "Mytron 12AX7A USA / ZCF \\". It has no other markings on it. Nothing etched in the glass or stamped on the base. The paper-thin mica's remind me of russian/chinese manufacture. The plates look nothing like any 12AX7 i've seen before.

It doesn't test anything like a 12AX7. The needle on my Hickok 800 spikes to its max and I have to raise the bias considerably (for example, into to 12AU7 range) before the needle relaxes at all.

Mytron12AX7.jpg
 
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The only 12AX7 type I have seen with plates like that is the Mullard CV4004. But still not quite like that I don't think (not at home so cannot look). Looks like a bunch of 12AT7's I have though. If you test as a 12AT7, does it seem in the right range?
 
Skylab- I tested it as a 12AT7 and it tested unrealistically strong. It tested at 7250 micromhos, where an average new 12AT7 should test no stronger than 4500-5000 micromhos.
 
It also became very hot, very quickly, on my tester. The filaments didn't appear too bright and the Line Fuse lamp didn't activate on the tester. I removed the tube quickly to avoid any damage, but I doubt I even want to experiment with this wacko tube in my precious gear, anyway.

Nothing about it suggests Mullard. There is no code etching and the glass is smooth (unlike the set of ridges on Mullard tubes).
 
isnt there a russian tube like 6p3s or something that is a high current tube that might be similar? It can be used in a 12ax7 spot in many instances, although some guitar guys use it as a 2 watt output tube.
 
Looks like a Mullard boxplate. I sold a couple a few months back that looked exactly the same. The boxplate tubes I had did not have the ribs on top of the tube's glass, nor was there any etched code, but they were marked 12AU7 / ECC82.

Larry
 
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Yeah, the photos I'm checking out now all have smooth glass and no etchings either. The "box plates" on my tube seem half the width of the Mullard photos I'm seeing. These plates are much narrower and have three holes punched in them, which I have yet to see on the CV4004 and CV4003.

Anyway, it's definitely the closest comparison I've seen yet.

Thanks for the input, everyone.
 
I'm reading about Brimar Longplate CV4003's, but I can't find any identical photos.

The super thin mica's are very similar to the mica's on my Brimar 6060 (12AT7) pair, which may lend some evidence here.
 
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