[R-390] tube testers

[bernie nicholson]

I have been repairing instrumentation with tubes in it since the 1960 s and have always been of the opinion that the best tube  tester is the circuit that the tube is in, it is easy to check the parameters of the circuit by measuring the voltage drops in the circuit i.e..  across screen resistors ,cathode/plate resistors ect ,with the mental application of Ohms law the currents are easily seen ,if no current is flowing the resistor is open circuit or the tube has no emission its as easy as that and all you need is a voltmeter, I never substitute a tube until I find a reason for problem,in my tool box I have a selection of tube extenders ,so voltages can be read easily above the chassis ,these are all home made from plugs  and valve sockets, there have always been people who had pretensions to being technicians and used to endlessly swap tubes around,in Australia we used to refer to them as valve jockeys , the large government department where I trained did have a tube tester in the lab and used to sample tubes from the manufacturer to check they were in specification , when you look at the original specification for a radio like the RCA AR88 it called for full performance from the radio if ANY or ALL of the TUBES were down  to 30% EMISSION ,the reality is that well engineered equipment doesn't make great demands on the tubes ,   Our family acquired a television set in 1956 it had 23 tubes by 1970 , most of the tubes were original , the only tubes that had been replaced were the horizontal O/P, damper diode , eht rectifier ,Ht rectifier, and a double triode in the cascade amp in the tuner, the monochrome picture tube also was at the end of its life, lots of people these days have the idea  that tubes are CONSUMABLE ITEMS  that need replacing every so often ,I often here people talking about RE TUBING their  rig ,,, WHAT A CONSUMMATE WASTE  OF PARTS AND TIME , Regards to every one , hope this is of interest .