Retronics

For those of us who have recently started repairing or constructing vacuum tube equipment like vintage broadcast receivers or audio amplifiers, this question is likely to arise: What tube tester should I buy?

If you post this question in an electronics forum, the answers may be contradictory and confusing:

• Some respondents will claim that you don’t need a tube tester, because the best way to test a tube is in the actual circuit. This is often true in a troubleshooting/repair process, but it presupposes that you’re certain that the rest of the circuit is working correctly. When designing a new device, and the circuit design has yet to be proven, or the circuit has yet to be built, in-circuit testing is not an option.
• Some will say that simple emissions tester is all you need. For quickly separating “good” tubes from the “bad” ones, this may work, but these testers don’t tell you much about how the tubes actually perform.
• A traditional transconductance tester will give you a better impression of the tube’s actual condition, and some respondens may want to sell you one of these, often at a high price or in poor condition. If you’re prepared to restore it before using it, this may still be a good option.
• For those building and repairing guitar amps, there are some tube testers specially made for this purpose, but these usually support only the most common audio tubes.
• When designing your own circuits, a curve tracer is preferable. On an amateur budget, high-end test equipment may, however, be out of reach. Getting an old curve tracer can be an option, but these are usually big and heavy, and may need lots of maintenance and calibration, and often have a laborious set-up procedure before each test.

Luckily, there is an option that gives you both the ability to measure single parameters like transconductance at a chosen bias point, and also perform curve traces for almost any combination of parameters, but still is compact, affordable and user-friendly. There are a few alternatives on the market, and they share the principle that most of the processing is performed by firmware and/or software, reducing the hardware costs to a minimum.

One of these is the µTracer 3+, which is sold as a kit with PCB, components and construction guide, at a reasonable price (currently €219 inc. worldwide shipping). I decided to give it a try.

https://www.dos4ever.com/uTracer3/uTracer3_pag11.html

The kit and the building process is described in my next post.