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Help Identifying 12AX7 tubes

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Posted on September 22, 2020 at 09:21:52
lehmanhill
Audiophile

Posts: 5
Location: SE Michigan
Joined: April 13, 2015
These are 12AX7GAP/R tubes removed from a Philbrick analog computer in the 70's. My father was working at AC Spark Plug and the analog computer was being decommissioned. He brought home a K2-W module including tubes and a couple of spare tubes for sentimental reasons.

Philbrick bought tubes from several manufacturers and had them relabeled as "GAP/R Computor" with a Philbrick part number. I'm not very good at identifying tubes, so I could use your help in understanding what they are and if they are interesting for audio. I have two which were used in the K2-W and two NOS spares. The GAP/R label says "Made in USA", but I would not bet my fortune on that.

Probably a dead giveaway is the gold paint octangle around the 12AX7 label. I've read about a "stop sign" label, but the rest of the description didn't fit these tubes, at least as I understand it.





The thing that is unusual is the getter. It is at an angle rather than sitting perpendicular to the plates. The getter is made from a wire bent in a 'C' with a stamped piece of metal closing the rectangle. The sheet metal has a couple of dimples in it.





Otherwise, it is a long plate (17 mm), ribbed plate 12AX7. On the bottom, in the center of the pins there is a letter in the glass. Mine have A, B, E, and R. There is also a faint number in the glass between pins 1 and 9. It is sometimes unreadable. I think I can see a 3 and a 5.

Any thoughts?

 

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RE: Help Identifying 12AX7 tubes, posted on September 22, 2020 at 17:11:01
Jim McShane
Dealer

Posts: 5839
Location: Chicago
Joined: January 13, 2003
It looks like a Tung-Sol 12AX7. The heavy numbering and the line above the elongated octagon are Tung-Sol markings.

 

RE: Help Identifying 12AX7 tubes, posted on September 23, 2020 at 07:34:46
Tom Bavis
Audiophile

Posts: 893
Location: Upstate NY
Joined: May 25, 2007
I have a Philbrick op-amp with 12AX7 "Computor" tubes with the Tung-Sol code 322.

 

RE: Help Identifying 12AX7 tubes, posted on September 23, 2020 at 08:55:37
lehmanhill
Audiophile

Posts: 5
Location: SE Michigan
Joined: April 13, 2015
Thanks Guys,

Based on the Tung-Sol suggestion, I was able to find images of Tung-Sol tubes with the exact same elongated octangle marking, so it clearly is a Tung-Sol. From the notes connected to the images, it seems to be 1950's, or more likely 1960's. That makes sense given the Philbrick analog computor era.

I haven't been able to find pictures that show the same getter design. There was one photo that might have been, but it wasn't clear enough to tell.

Tom,

What do the getters in your Tung-Sol "Computor" tubes look like?

Alas, the part number on mine starts with 322, but it is white like the GAP/R marking, so I wasn't sure that was a Philbrick part number or a tube manufacturer part number. Given the elongated stop sign, I guess it counts toward Tung-Sol.

I know that era Tung-Sol can be good audio tubes, but I continue to wonder about the angled getter. Unfortunately, I don't have a 12AX7 audio device to try them in.

 

RE: Help Identifying 12AX7 tubes, posted on September 23, 2020 at 11:50:38
Jim McShane
Dealer

Posts: 5839
Location: Chicago
Joined: January 13, 2003
I wouldn't have told you it was a Tung-Sol unless I was sure it was a Tung-Sol!

Also 322 is the EIA code for Tung-Sol.

Finally the getter shape is typical of early production Tung-Sols. Later tubes had round getters. The fact that your tube is a 12AX7 (not a 12AX7A) and that it has a square/rectangular getter simply means it is an early production tube. The fact that it is on an angle is just the way they made it in some of their early tubes.

If the tube has a 4 digit code after the "322" you can decipher the date of manufacture - the first two numbers are the calendar year and the second two are the week. For example 5922 would mean the 22nd week of 1959.

 

RE: Help Identifying 12AX7 tubes, posted on September 23, 2020 at 15:12:11
lehmanhill
Audiophile

Posts: 5
Location: SE Michigan
Joined: April 13, 2015
Thank you very much. That answers all of my questions.

I didn't understand that a relabelled tube would have followed the EIA code, but obviously they did. Thank you for being patient with a tube rando like me. I'm learning, but have a long way to go.

Based on your response, my tubes have a date code showing the 35th week of 1956 which is appropriate because the Philbrick K2-W started production sometime in 1952.

 

Nice tube!, posted on September 24, 2020 at 07:25:58
samstone
Audiophile

Posts: 378
Location: midwest inner city
Joined: August 11, 2002
Yes the manufactring codes can be tricky to figure out sometimes. I have some tubes that are re-branded to one manufacturer and are actually another. GE and Sylvania did this on more than one occasion. The trick that Jim mentioned is finding the code. IIRC GE is "188", Sylvania is "312", RCA is "274", Raytheon is "280". Again I could be off on my numbering, but somewhere online is a tube manufactring ID chart.

 

RE: Nice tube!, posted on September 24, 2020 at 11:44:59
lehmanhill
Audiophile

Posts: 5
Location: SE Michigan
Joined: April 13, 2015
Thanks, Sam. I am learning, but there is so much to know. I don't have a current use for 12AX7, but I seem to keep adding tube gear over time, so I will keep them for sentimental value and with the hope of hearing them in the future.

Jac

 

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