The Precision 912 Tube Tester


This is a Precision Model 912 Tube Tester. I obtained this when I was sixteen from a rather thin wiry fellow who owned Waltís TV Radio Repair, a small appliance/TV/radio fix-it shop that was in my neighborhood. It seemed he fixed just about anything that could be carried in. He did both in-shop repairs as well as in-home TV servicing.

I started to visit his shop when I was 14. I would go and watch Ė and try not to get in the way. He would give me radios and other electronic stuff his clients didnít want repaired because it cost too much to fix.

Harkening back, I think I started going to his shop to get advice. As I said somewhere in one of these pages, I fixed appliances for people in my neighborhood to earn money after school. I would go to the drug store to test tubes. However, I found this tester to be very rudimentary and sometimes wrong. I guess I then got the bright idea of going to Waltís and using his tube tester to test tubes Ė of stuff I was fixing for my neighborhood clients. I would sometimes buy parts from him. But he didnít always have the parts I needed. I mostly got these from Radio Shack. Remember gold-pin Lifetime Tubes?

Walt was often way too busy to talk. Towards the end, though, when his business started falling off, he would spend more time with me. In 1966 when I was 16, Walt decided to close his business to work for a manufacturer repairing their electronic equipment. He said he was getting out of the business because everything was going Japanese made solid state. At the end, he sold me the tube tester. I seriously doubt I cut into his business. I never really went on house calls or fixed TVs and I didnít fix things that were out of the scope of our small neighborhood.


Since Iíve had this tube tester, it has been very good at testing and analyzing tubes of all sorts. With the exception of compactron tubes, this tester has tested anything I could plug into it.

The common single electrode structure vacuum tube only has one function. The compactron vacuum tube is a type of vacuum tube that contains multiple distinctly different electrode structures packed into a single glass envelop. They were introduced in 1966 by GE to compete with early transistor electronics and were mostly used in televisions, some really rare radios, a few PA amplifiers, as well as some industrial applications.

A few of the many adapters that were available.

From the first commercially available vacuum tube (the 01 or CX201) to the last or latest 9-pin tube, my 912 can accurately test them all. This thing could also test the emissions of a lot of early picture tubes. Now, there may be some exotic or high power tubes that the 912 wonít test. But be it eye tubes, car radio vibrators, this thing tested them all.

Note. Sometime since 1966, my nuvistor test socket adapter got misplaced. The only time I needed one was when I was working on this Watkins and Johnson industrial hybrid VHF receiver. I thought of making an adapter but I never got around to it.

There may have been physically huge more accurate tube testers that cost thousands, but my small 912 could diagnose and find what I needed it to do. If the tube was weak, if there was a short, or if the tube was mismarked, I could determine the problem. It could also be used to accurately match pairs of tubes.

I think it was a good tester because this piece of test equipment was so popular among the repair community and the various models were around for such a long time. The company kept making add-ons and updating testing parameters and documentation Ė even after tubes started being phased out. Itís small, doesnít take up a lot of room and it works.

Notice the tube? It's a 4-pin 80 rectifier.

Despite it being over 70 years old, it can do what it does because I kept it clean, maintained, calibrated, and correctly adjusted. On occasion I did replace several of the tube sockets, one of them twice. With use, they do wear out over time.

Yes, I know. There always seems to be one or two reasonably priced on eBay.

SteveS December 2018


Note.  The 80 rectifier tube was introduced by RCA in the late 1920s. Because the 4 pin structure was so rugged, it was used in industrial equipment up until the early 1950s.