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Simpson Tube Checker

   There was very little in the way of stand alone test equipment for a spark transmitter wireless station. The wireless transmitter equipment, while physically large, was simple and came equipped with built in metering to monitor the diesel engine generator's voltage and current output, plus an ammeter in the antenna. The first receivers on the coast were magnetic detectors, so named because of the horseshoe shaped magnets comprising the bulk of the unit. These receivers were mechanical in nature and required the operator to wind the clockwork mechanism. Screw drivers, pliers, wrenches and the like be the tools required to get an early station back on the air.
   The operators on the stations were trained to trouble shoot the equipment they operated, and had to demonstrate they were proficient in order to receive their operating licenses.
   The operators soon learned to listen to their transmitter's spark crackle. Many signs of an impending failure would be reflected in the sound of the spark. Trouble shooting would entail noting any irregularities in the readings of the supply voltage and current, or the current flowing in the antenna. Faults most likely would appear, as they still do in today's equipment, where ever there is heat or stress. High voltage transformers, the spark, and the capacitors would all be likely suspects. Many of the repairs could be made with simple tools and parts made from the operator's junk box.
   Wireless technology improved and by the late 1920's spark transmitters and associated receivers were being replaced by vacuum tube equipment. Servicing became a magnitude more difficult and specialty test equipment was required. Something to test the vacuum tubes was required.
   Vacuum tubes could develop shorts/leakages between their internal elements, and more likely, a reduction in cathode emission. Wireless technology improved and by the late 1920's spark transmitters and associated receivers were being replaced by vacuum tube equipment. Servicing became a magnitude more difficult and specialty test equipment was required. Something to test the vacuum tubes was required.
   Vacuum tubes could develop shorts/leakages between their internal elements, and more likely, a reduction in cathode emission. A tube checker, such as the Simpson Model 222 (late 1930's) in the photo, would test for these faults. Tube to be tested would be removed from the equipment, the checker's switches set as the Simpson handbook would specify for that particular tube, the tube inserted, and result seen on the meter in the middle of the instrument.
   This model checked for inter-electrode leakage, cathode emission and filament operation--a basic test.

   Of course the larger transmitter vacuum tubes could not be plugged into a checker. In that case, if the transmitter's own metering didn't tell the tale, a simple removal and substitution of the suspect tube with a known good would be made.
   A tube checker, such as the Simpson Model 222 (late 1930's) in the photo to the left, would test for these faults. Tube to be tested would be removed from the equipment, the checker's switches set as the Simpson handbook would specify for that particular tube, the tube inserted, and result seen on the meter in the middle of the instrument.
   This model checked for inter-electrode leakage, cathode emission and filament operation--a basic test.
   Of course the larger vacuum tubes used in transmitters could not be plugged into a checker. In that case, if the transmitter's own metering didn't tell the tale, a simple removal and substitution of the suspect tube with a known good would be made.


DayRad Radio Set Tester

   In the 1930's the next step up from a simple tube checker would be this device made by the Dayrad Corporation based in Dayton, Ohio.
   Called the "#52 Radio Set Tester" it is designed not only as a simple volt, ohm and current meter but also as device to go in series with the tube under test. The radio repairman would remove a suspicious tube from the radio, plug the tube into the Dayrad, then plug a cord from the Dayrad into the vacant tube socket. Then by manipulation of the Dayrad's switches the various voltages and currents at the tube could be measured under operating conditions. What the added distributed capacity of the interconnecting cable did to the receiver's tuned circuits can only be imagined.
   Dayrad was eventually became part of the Bendix Corporation.
   Manual is available here.

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