How to ID 12AX7 manufacturer?

[casey73]

I pulled 9 12AX7A's from a small Silvertone organ I got at a garage sale. I plugged them all into my benchtop "champish" amp and they all work. I didn't do any measurments to see relative strength (and don't have a tube tester) but I'm assuming they would be fairly close since they are obviously the original tubes. They are all have identical markings, down to lot/date codes, and are labeled Silvertone. They look like RCA, and I did a side by side comparrison with an RCA 12AX7A that I already had and they are identical in construction, grey ribbed plates, halo getter, etc.. So, is it pretty safe to say they are RCA?

[Bruce / Mission Amps]

Look to see if the "12ax7' ink printed on the glass is inside an 8 sided box... if so yes RCA.

[casey73]

Yup, with a tiny MADE IN USA above that. Thanks Bruce!

[bob p]

I know that I'm coming late to the party with this information, but RCA was an OEM supplier for Silvertone back in the day, so you're right to consider RCA among the list of suspected manufactuers.

I got lucky and pulled a Silvertone Twin Twelve head out of the garbage one day. It had been thrown away because of an intermittent short that was causing the amp to cut in and out intermittently. (It turned out to be a loose volume pot that just neeeded to be tightened down to the faceplate!) In addition to having period-correct ghost-manufactured Silvertone and Fischer preamp tubes, it had the original Silvertone/RCA blackplate 6L6 in it. That was a good day.

[Lightning13]

Fast forward 4 years to 2011.

A few days ago I was going through a box of old tubes and found a Silvertone 12ax7. So, I installed this in my 5F1 champ. Man, that tube really warmed up the sound. With a little research I found out it's a sought after RCA tube that was rebranded. Now, I have to decide whether to play it or save it for recording.