I don’t often work on test equipment, but sometimes I take a tube tester or similar for service. This one in particular is a 1951 EMC Model 211 tube tester, a quick and simple emissions tester offering a handful of socket types for commonly needed tubes of the era.
This one had been stored in its original box for many years and was in very good cosmetic condition.
By the time this tester was released, 7- and 9-pin miniature tubes were common (and Nuvistor tubes turned up occasionally, although never entered wide popularity as was expected.) Octal tubes were largely relegated to just being rectifiers and output tubes, and Loctal tubes had disappeared almost entirely. Owing to a lack of compatible sockets, this tester isn’t able to test anything prior to the mid ’30s when Octals were released.
It’s an exceedingly simple design, with one adjustment, an electrolytic and a paper capacitor in the circuit. One resistor appears to have been replaced at some point in the past, too.
Not much to it!
Shown here working! This tester isn’t especially accurate or sensitive, it’s the sort of thing a technician might bring out to a home on a service call rather than a benchtop model with more features, but it broadly agreed with my Precision tester. Good as new!