Lafayette Model TE-50 Tube Tester
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Tube Tester

One of the disadvantages of vacuum tube is its limited lifetime. Burnt out heater is quite common failure. However most of the tubes are no longer manufactured, so it is natural to buy spare tubes. Getting many junk tubes at a flea market, check the continuity of the heater by an analog circuit tester... If the heater lights when a battery is connected, it promises the further life of equipment in which the tube is used.

As I studied the vacuum tube electronics, however, I learned a problem so called low emission. Cathode material deteriorates after hours of usage or storage, less electrons flow within the tube. Poor performance may result if emission is not enough. Another problems are the heater leakage and short between electrodes. Therefore it is not always possible to examine the tube condition by the heater continuity check. Tube Tester is desired.
Lafayette TE-50 Tube Tester: click here for larger image

Lafayette TE-50

Lafayette TE-50 is a simple and compact Tube Tester primarily used by radio servicemen. It can perform heater test, short test and emission test. It cannot provide characteristic tests which are possible by a laboratory grade tester, however, still it is very convenient.

Bottom half of the cabinet of this tester is a drawer in which a operation manual and tube setting instruction can be stored.

Operation is a little bit complex. Each switch arranged in-line is to be set either to ground, heater, plate or no-connection, depending to the tube type. Heater voltage is to be set by a rotary switch. "Load" control must be set according to the each tube type by referring the datasheet. Set the mode switch to QUAL, insert a tube into the socket, wait until tube becomes operational, then examine the reading of the meter. If it indicates GOOD, you feel happy.

Even if the meter reading shows NG, there may be a chance for that tube to be used. Not all of the circuits require full emission. After all, you can use that tube if your equipment works satisfactory.
Click here to view the manual (PDF 3072KB)

Circuit of the tester is quite simple, as you see it on the diagram shown here. It has no voltage regulator, so you cannot get absolute result unless you calibrate the power supply voltage.

The power transformer provides many voltages for heaters, and is an auto-transformer. The power switch of this tester has HI and LO position. If the line voltage is between 115 and 125 volts, HI position is used. If the voltage is between 105 to 115 volts, LO position should be used. When LO position is selected, the auto-transformer steps the voltage up so that enough voltage is applied to the plate of the tube.

The tester has no protective circuit. Improper operation may result in the damaged tester and/or the tube.
TE-50 Circuit Diagram (Click for larger image)

The seller of this tester said "virtually new condition" on his ad. Panel and meter is in excellent condition indeed. However, paint surrounding the slide switches shows apparent wear, indicating considerable amount of usage. 9 pin socket terminals are worn. The previous owner used this tester with great care.

All of components are mounted on the panel. No dust or rust observed, it is quite like new. Wiring to the tube sockets is colorful. Japanese made capacitors of 1960s are desired to be replaced, as they tend to show excessive leakage.

Because this is a Lafayette in 1960s, it is of course made in Japan. Not sure which company manufactured this unit - Leader, maybe? - Then one of our visitors, Mr. Jaak van Waeg from Brussels, wrote that it is identical to the Kyoritsu Model K119. Thank you for your info, Jaak.
TE-50 Inserior View (Click for larger image)

Method becomes purpose

Checking the spare tubes was the original reason to buy this tester. When the tester is obtained, however, started to buy many junk tubes to use the tester. When the original purpose is forgotten, a vacuum tube fan became a vacuum tube mania. I began understanding the feeling of gentlemen who own thousands of tubes. How dangerous.....

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Copyright (C) NoobowSystems Lab. San Jose, California 1999
Copyright (C) NoobowSystems Lab. Tomioka, Japan 2000, 2002, 2004

Jan. 24, 1999 Created.
Jan. 30, 1999 Revised.
May. 05, 2000 Reformatted.
May. 10, 2002 Revised.
Aug. 17, 2002 Reformatted.
May. 16, 2004 Reformatted.