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Identifying old vacuum tubes


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My grandfather, who turned 95 this year, is a retired electrician. A few weeks ago, when helping him move some things around in his basement, I opened a few of his old tool boxes and found several hundred old vacuum tubes. Being the owner of a couple tube amps, I'm intrigued by this discovery but digging through piles of tubes, I'm having a hard time figuring out exactly what I'm looking at. Specifically I found a whole bunch of tubes that look vaguely like 12AX7 pre-amp tubes. They're mostly from GE and RCA but I also found a Mullard and a couple Tung Sols. Unfortuntately, only a couple of them say 12AX7 on them. Most of them say 12AU7 and several of them have other designators that are greek to me. My question is, what is likely to happen if I pop a few of these into my Fender Blues Junior in place of the 12AX7s? Is it safe to experiment like that? Are 12AU7s interchangable with 12AX7s? Does anyone know where I can find a list of other tubes that are compatible with 12AX7s?




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Post this in the feel free to ask myles thread at the top of the forum. He knows all about this sort of thing. Yes you can use any 12AX7 tube you find for the rest you need to have a tube cross reference in order to safely use the tubes you have found.
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Jason...sorry to be late to this thread. Do not just pop tubes into your amp. You must BE SURE that they are compatable first.


As mentioned, Myles is expert at all things tubular!!


They might be worth something.....old tubes can be "in demand", of course depending on which tubes they happen to be!!



"There once was a note, Pure and Easy. Playing so free, like a breath rippling by."






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You may get lucky and "pop in" some that are still good tubes...

...but with hundreds of tubes...you really need to run them through a decent tube tester to see how they measure out...and if they have any shorts.


I have a fairly high-end tube tester ((Precise model 111) that I use on all my tubes before I pop 'em in to any of my gear.

It's amazing how many tube sellers claim their tubes are a certain quality...and when I test them...I get a different results.

Mostly because many of the guys on eBay have lousy testers that only test with *good* to *bad* scales...but those just measure emissions and nothing else.


Anyway...if the tubes are known to be good...you can swap 12AX7/12AU7/12AT7 tubes and each will change the sound of the amp to a degree.

What works best...well...depends on the amp in question.


miroslav - miroslavmusic.com


"Just because it happened to you, it doesn't mean it's important."

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Thanks for the info guys. I did post in the ask Miles thread as you suggested and he posted a prompt reply. Yes indeed, my gramps is quite a man. Unfotunately, he doesn't have 100% of his marbles left these days but as of a few years ago he was still offering to "fix" my guitar amps for me so they wouldn't make that terrible distorted sound :) Luckily, I also found a tube tester in his basement so I'm going to test a bunch of these out and see what I've got.


Thanks again,


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