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The text below is my feeble attempt at writing a white paper on this tester, but nothing can compare to the Navy’s original specifications. Reading this one cannot help but to be impressed with the tester that resulted from these specifications, and also the designers that implemented it. Click here for the 273 page pdf, and here for the supplement. Below is just an oversimplified summary.

 

The Cardmatic tube tester is an ingenious design.  Various power supplies, a gm bridge circuit for measuring transconductance, a decade resistor box, and an accurate metering circuit are all connected together at the card reader so that anything can be connected to anything.  Replace the card reader contacts with relays and you have an ideal platform for computer control.

The tester is capable of at least 17 different test configurations, ranging from simple triode transconductance tests to high voltage rectifier tests to voltage regulator tests.

We'll start with the shorts test.  One of the functions of the power supply is to supply a regulated positive and negative 150VDC.  Among other things, these voltages are used for the shorts tests.  They are applied to the tube elements in the opposite polarity from normal.  This means no worry of cathode stripping, and any sort of grid emission will cause a short lamp to flicker.  If there is enough leakage between any elements to allow enough current to flow to light a neon lamp, then the tube is defective.  The sensitivity of the shorts test is adjustable and is part of the calibration procedure.

At the same time, the meter is placed in series with the heater and cathode to measure heater/cathode leakage.  The meter can be programmed to reject tubes with as little as 10 uA of leakage current or as much as 170 uA.  It can also be disabled, which is done in the case of directly heated filamentary tubes.

For the quality test, the tester can be configured a number of ways depending on the tube to be tested.  Here are some examples:

Transconductance Test:  

·  Full scale meter reading can be programmed from 500 to 128,000 uMhos in 100 uMho steps.

·  The tube can be in grid bias or self bias mode.

·  Negative grid bias, if used, can be set to -.1VDC to -99.9VDC in .1 volt steps.

·  In self bias mode, the cathode bias resistor can be anywhere from 0 ohms to 70K ohms in 10 ohm steps.

·  In self bias mode, the cathode bias resistor can be bypassed by a 1000uf capacitor.

·  A regulated signal voltage of .222VAC is applied to the grid.

·  The plate voltage is regulated and can be from 10VDC to 260VDC in 10 volt steps.

Plate Current Test:

·  Full scale meter reading can be programmed from 100 uA to 500 mA in 100uA steps.

·  The tube can be in grid bias or self bias mode, or can be a diode.

·  Negative grid bias, if used, can be set to -.1VDC to -99.9VDC in .1 volt steps.

·  The plate circuit resistance can be set anywhere from 0 ohms to 70K ohms in 10 ohm steps.

·  The plate voltage is regulated and can be set from 10VDC to 260VDC in 10 volt steps, or an unregulated 360VDC, or up to 1200V P-P AC.

Knee Test for Sweep Tubes

·  High current test where the tube is having to charge/discharge a large capacitance as its load.  Most testers lack this test.

These are just a few of the more common tests, and we've already hit quite a few different combinations of test configurations.  Since most of the more obscure test configurations are used only for tubes that are already programmed into the database we will not go into details here.

During the gas test, the tester simply measures grid current.  If there are gas ions present in the tube, they will be attracted to the negative grid and grid current will flow, causing the meter to deflect.  If it deflects above the green area for gas, then more than 3 uA of grid current is flowing and the tube should be rejected.

This tester also has:

·  A filament power supply that is programmable from .1 volts to 119.9 volts in .1 volt increments.

·  An auxiliary B+ supply that is regulated and continually adjustable from 30 to 300 volts (used mostly for voltage regulator tube tests).

·  A bias off supply that is used to keep unused tube sections biased off during tests.

·  A test button that allows us to test two identical sections within a tube with one test.

·  Protection circuits that automatically shut the tester off in case of power supply overload or grossly off scale meter deflections.

All in all, one nice tester!

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04-14-2016