Identifying an unknown tube

[Rispoli]

Hope someone can help. I recently purchased a pair of rare (50 pairs made) Antony Michaelson mono tube amps (Chronos). There are 2 tubes on the input/driver board. One is a 12AT7 and the other is an unknown GE brand. This tube is slightly taller and has 2 grid plates at the top with no halo. Is there a way to identify this tube with no markings? A third part suggested it is a 12BH7, but how can I be sure? thanks in advance for any info, Rispoli

 

[gianis]

tube

Please post a pic from this tube...

 

[diesel_tech]

Put the tube in the freezer for a few moments, take it out and breath on it and look for a ID that might have been rubbed off. Some times this works and sometimes it doesn't.

Jeremy

 

[sorenj07]

watch out, make sure you don't heat the tube up quickly after cooling it, or it could break due to the stress.

 

[Rispoli]

thanks for the responses so far. I have included the best picture I could given the byte size limitation. Perhaps this will look familiar to someone....

 

[planet10]

http://www.diyaudio.com/forums/showthread.php?s=&threadid=37414

http://www.diyaudio.com/forums/showthread.php?s=&threadid=85943

http://www.diyaudio.com/forums/showthread.php?s=&threadid=14116

You might get some info from the above threads.... you could also contact Musical Fidelity

dave

 

[Tom Bavis]

GE tubes usually have a large etched number... occasionally faint, but pretty durable. 12BH7 or 6CG7 seems most likely, but 6829 and 6414 are tall like that too... pinouts are same as 12BH7, but heater current is different.

Bring one over, and I'll plug it into my tester. I live in Macedon, work in Henrietta... not far from you.

 

[Ty_Bower]

That tube looks exactly like the 12AZ7N that Angela is selling. You'll find lots of 10 of them for sale on eBay.

If it really is a 12AZ7N, there's a vague reference to it here:
http://db.audioasylum.com/cgi/m.mpl?forum=bottlehead&n=68891

I've found it very difficult to turn up much info on this tube. I can't figure out if it is most like a 12AZ7, a 12AT7, or a 12AV7.

Here's a couple photos of one of the tubes from the lot of 10 I bought. Does your tube look like this? It appears to have a D shaped getter. There are no identification markings of any kind on the tube.



By the way, one of mine has a tiny piece of glass running around loose inside.

 

[Tweeker]

12AZ7

Datasheet says it is a high mu VHF tube, mu and gm same as 12AT7 at same cited operating points of 3.7ma and 10ma. 12AV7 is medium mu, and is best left to non linear duties.

I would guess the 12AZ7N has near very similar electrical properties to 12AZ7, rather than 12AV7.

 

[Ty_Bower]

I would hope that the "12AZ7N" is more like a 12AZ7. But, in the link to the Bottlehead Forum, Ron thinks it is like a 6829 - which is closer to a 12AV7.

 

[Tweeker]

He also cited a gain of 60.

 

[kenpeter]

AZ=AT with improved Heater-Cathode voltage.

At least thats what Zobsky told me bout an AZ
that I had given to him for troubleshooting his
circuit (originally with an AT) that had oscillation.
Turns out the tube had nothing to do with it...

Its a fine substitute, use it.