BY STEVE JOHNSON ( )
From the late 1920s through the 1950s radio and television repair shops were almost as common as drug stores. Back then you could take your radio, TV, or record player to your neighborhood shop and have it repaired. If it was too large to take in, a serviceman would actually come to your house with the tools and parts to make your set perform like new again. In larger metropolitan areas, this usually meant the serviceman had to climb several flights of stares carrying meters, a case of spare parts, replacement vacuum tubes, and a tube tester.
In the early 1930s, the need for servicemen to become more efficient at troubleshooting while carrying less spurred the development of portable set testers. These all-in-one testers could accomplish most of the tests and measurements required to diagnose a problem on site. In addition, students fresh out of service training schools on a limited budget could set up shop with fewer pieces of test equipment by purchasing a set tester that would perform most if not all the tests required to troubleshoot circuit problems on the bench or on a service call.
Early set testers
The 1932 Supreme model 56 Radio Analyzer performed several tests, including voltage and resistance readings along with testing tubes. The model 56 used Bakelite “Master Plungers,” which the operator inserted into jacks to make function selections. The 56 was not AC powered. The cord plugged into the radio or amplifier socket of the tube under test, and the tube plugged into the tester, which was powered by the radio.
Supreme Model 56 Radio Analyzer
The tester had separate internal batteries for supplying power to make resistance measurements. The model 56 was also offered as a kit and could save the serviceman $6.96 by building it himself instead of buying a factory-assembled unit.
Hickok 4900-S Set Tester
Not all set testers were capable of testing tubes. The 1937 portable 4900-S Set Tester by Hickok measured capacitance, resistance, AC and DC milliamps, and AC and DC volts up to 2,500 volts. It had no cable to insert into a tube socket and did not have the capability of testing vacuum tubes. A service person using this unit would have had to also carry a tube tester on service calls.
The Hickok SG-4800 Radio Set Tester
The Hickok SG-4800 set tester was manufactured around 1930 and used several adapters to connect to a radio's tube socket. The SG-4800 measured AC and DC volts, resistance, capacitance, and DC milliamps. The tester was battery- and AC-powered and required five batteries to perform various tests and supply voltage. It had a battery connection chart glued to the inside bottom of the case.
The SG-4800 had a test point connected to each pin on the tube test socket so a meter probe or jumper could easily be attached to each tube pin. This fairly new testing concept of providing test points for attaching external probes for taking measurements became known in the 1930s as “free-point testing.”
Today any of the very early Hickok test equipment is sought after by collectors and although outdated, the equipment commands quite high prices in online auctions. It is not uncommon to see an early example in very good condition sell for a few hundred dollars. Swap meets are usually the best place to by early Hickok equipment, and finding an early Hickok piece for under $100 is not uncommon.
Free-point testing
The concept of “free-point testing” or “free reference point testing,” as it was sometimes called, brought each pin in every tube socket out to a row of jacks on the tester to allow the serviceman to easily hook up a meter to test input, output, and voltage of each tube. The serviceman could now connect a probe to easily inject or test for a signal on every pin of the tube or the socket in the radio chassis. Free-point testing did not require any adapters or clips on the socket to attach meters to the pins while the tube was operating.
Although test points in circuits are common today, the advantage of having test points for troubleshooting these early circuits and tubes was a new concept and many test equipment manufacturers vigorously promoted this new feature found on their set testers and analyzers and published documents on the “Free-Point” System of troubleshooting.
Triplett model 1220-A Free-Point Tester
The Triplett model 1220-A “Free-Point Tester” used a cable with tube socket adapters to allow in-circuit free-point testing of tubes using separate meters. All this simple unit provided were sockets and jacks for external connections when the tube was removed from the chassis and inserted into the tester. When the tester's cable was inserted into the chassis tube socket using the appropriate adapter, measurements could be made from the jacks on the tester.
Weston 774 Type A Tube Tester/Analyzer
The Weston 774 Analyzer was built for the U.S. Army Signal Core and had several free-point sockets and adapters to test radio circuits using the tube socket pins. It had a built-in tube test point adapter which is used as a free-point adapter.
None of the set testers discussed here that were manufactured before the 1950s have much use today besides collector value. Although tube audio equipment has had a resurgence in popularity lately, these set testers were manufactured before most of the popular 1950s and 1960s vacuum tube equipment was designed and are not capable of testing the later vacuum tubes. For that reason most are only sought after for display in collections or as conversation pieces. Prices will usually range from $40 to $150 depending on condition and if they still have the original literature and manuals.
A collection of tube socket adapters
By the late 1940s, having easily accessible test points for each tube pin became the norm in troubleshooting techniques and the term “free-point testing” disappeared. Simple tube socket adapters with built-in test points for each pin appeared. There were a number of tube socket adapters because by then there were many different types of tube sockets. A socket adapter could be quickly placed in the tube socket with the tube plugged into it for quickly connecting a probe to any pin. It was common in the 1950s for any serviceman's kit or repair bench to have several different size tube socket adapters on hand.
Today many of the more common adapters may be found and usually sell for between $5 and $10 each. Finding a full set is harder but purchasing a set will most likely cut the cost per adapter in half over finding individual adapters.
Transistor set testers
In the late 1950s and early 1960s the idea of having one piece of test equipment for troubleshooting carried over into transistor circuit servicing. Transistorized equipment began replacing vacuum tubes as early as the mid 1950s. The reduced size of these newer transistorized consumer products meant less in-home service calls and more repairs in the shop.
The B & K the 960 Transistor Radio Analyst
B&K produced two popular service grade bench models, the 960 and the 970 Transistor Radio Analysts. These were designed to troubleshoot the new portable transistor radios. The model 960 transistor analyst contained a two-band AM signal generator, a vacuum tube voltmeter circuit, a stepped DC power supply for supplying battery power, a transistor-testing circuit for testing both PNP and NPN transistors in and out of the circuit, a speaker tester, and a low-voltage multimeter. The later 970 transistor analyst expanded on many of these functions and included FM in its signal-generating capabilities.
Although they both had handles, the 960 and 970 were primarily purchased by small repair shops for use on their service bench. Today these units in good working condition may be found for $50 to $150.
Today these vintage set testers remind many of us of a time when electronic repair shops were common and just about anything around the house that plugged in could be taken to a local shop for repair.
For more information and examples of early electronic technology, view my collection at StevesAntiqueTechnology.com
Advertisement
Learn more about Electronic Products Magazine
