I recently got this question in the mailbag, and it seemed like a good one to answer:
What’s the best multitester for vintage radio repair?
That’s actually a tougher question than it seems. The short answer? Well…it depends a bit, but most multitesters (not to be confused with multimeters, which are very useful) aren’t that useful for vintage radio work. They’re not a bad thing to have, but most of their functionality is lost on a vintage radio.
To re-cap, a multitester is a neat little microcontroller instrument which can do quick analysis of 2- and 3-terminal devices. It’s useful for checking capacitor value and ESR, quickly checking transistors and FETs, checking diode voltage drop and capacitance, measuring DCR and inductance of coils, and low-ohms resistance measurements. Powered by a 9V battery and a microcontroller, these devices take a lot of the guesswork out of quick go/no-go checks for a variety of types of electrical components. The most common model is the MK-168, available from a ton of different vendors primarily on eBay for $20-50.
The trouble with these devices for vintage radio repair is that you won’t end up using them all that often. Resistance measurements for vintage radio can easily be handled by most multimeters, like those in my Basic Tools round-up. Transistors started turning up at the very, very end of the tube radio era and you’re unlikely to encounter one of those hybrids and multi-testers can’t do anything for a tube beyond what a regular multimeter can. While DCR and inductance of coils is occasionally something to consider, more often than not you’ll have a good coil or an open coil and not a lot of in-between. And with vintage radios (and even most stereo gear through the ’80s) it’s just not worth it to test individual components before replacing; you’re better off just replacing all the parts subject to failure at once regardless of what they might measure. Not to mention, with a 9V battery supplying the power, you’re going to be far below the hundreds of volts found in most vintage devices.
That said, if you want the vintage equivalent of a multi-tester for a vintage radio, you do have a few options.
First would be a signal tracer. Signal tracers are fairly straightforward devices with a probe, detector, amplifier, and speaker. By injecting a tone at the antenna terminals of your radio under test and moving the probe through the signal path, you can find where it disappears. The probe can detect an AM RF or IF envelope and turn it into audio or amplify a small audio signal to find out which stage of the radio fails to pass a signal. These fell out of fashion after about the 1960s, but you can still find them on eBay. They were typically made by bench service companies like Conar, EICO, Heathkit, Knight, PACO, Superior Instruments, and others. They’re all pretty much the same – although being old gear, if you buy one you’ll want to make sure it’s in good working order (or you refurbish it) and the probes, if any, are provided. You should pay less than $100 for a fully working model. You’ll need a signal generator to go along with the tracer, of course.
Secondly, if you have a bit bigger of a budget or like rare test equipment, you might consider an RCA-Rider Chanalyst.
These are pretty rare and hard to find, but they’re unprecedented if you need a full functioned signal tracer and generator. These offer RF and IF generators, an oscillator injector, a power meter, and audio output (and you can even hook the various stages together and use one as it’s own radio if you wanted!) Sadly, though, these are rare and expensive and aren’t any better than a signal generator+signal tracer combo.
In general, though, I’m not sure I can really recommend a signal tracer if you’ll be doing more repair work than just vintage AM tube radios. They have little use in an FM radio, stereo receiver, or even most other electronics projects beyond a radio with the AM broadcast band and a 455-ish KHz IF. I used to have one, and used it once or twice very early on, but quickly moved up to other test gear and it sat taking up bench space until I finally got rid of it. About the only place they have any real use, in my opinion, would be tracking down issues with a radio’s front end – between, say, the antenna coil and a first RF amplifier ahead of the mixer – where signal levels might be too low for most oscilloscopes to display. Signal injection with a generator would likely be able to overcome this limitation, though.
So, in conclusion: in my opinion, a multi-tester isn’t a great tool if you’re just doing vintage radio repair. You’ll be better off with a plain old signal generator and tracer (along with your multimeter and standard bench tools) for your first set of vintage radio repair tools, if you’re not sure about taking the plunge for bigger and more expensive test equipment. Multitesters are fantastic little devices, but have limited applications in vintage radio repair, and so you’d be better off saving your money if that’s all you’re planning on working on. As far as signal tracers, while they are useful for vintage radio repair, they do have a limited usefulness beyond AM radios so keep that in mind when deciding if one is right for you or not.