Tube tester
From Wikipedia, the free encyclopedia
This article is an orphan, as few or no other articles link to it. Please introduce links to this page from other articles related to it. (February 2009) |
A tube tester is an electronic instrument designed to test certain characteristics of vacuum tubes. Tube testers evolved along with the vacuum tube to satisfy the demands of the time, and this evolution faded with the tube era, yet with the High-End advent, they became a pricey piece of equipment. The first tube testers were simple units designed for specific tubes to be used in the battle fields of WWI by radio operators, so they could easily test the tubes of their communication equipment.
Contents[hide] |
[edit] Types of tube testers
[edit] Filament continuity tester
The simplest one is the filament continuity tester, usually with a neon lamp connected in series with the filament and a current limiting resistance fed directly by the mains.
[edit] Emission tester
Next in complexities is the emission tester, which basically treats any tube as a diode by carefully connecting the cathode to ground, all the grids and plate to B+ voltage, feeding the filament with the correct voltage, and an ammeter in series with either the plate or the cathode. This effectively measures emission, the current which the cathode is capable of emitting, for the given plate voltage, which can usually be controlled by a variable load resistor.
Older testers may call themselves Plate Conductance if the ammeter is in series with the plate, or Cathode Conductance if the meter is in series with the cathode.[1]
The problems of emission testers are:
- they do not measure key characteristics of tubes, like transconductance
- they do not perform the tests at real load, voltages and currents
- they test the tube under static conditions, which are not even near the dynamic conditions the tube would work with in a real electronic device
- tubes with grids, might not even show the real emission because of hot spots in the cathode, hidden by the grids under normal conditions
[edit] Short circuit test
Usually, emission testers and better testers have a short circuit test which is just a variation of the continuity tester with a neon lamp, and which allows to identify if there is any shortcut between the different electrodes.
[edit] Mutual conductance tester
The mutual conductance tester, tests the tube dynamically by applying an AC voltage to the control grid, and measures the AC voltage obtained on the plate, while maintaining the correct DC voltages on the plate and screen grid. This setup actually measures the AC gain of the tube, rather than the actual transconductance.
[edit] Dynamic conductance tester
The dynamic conductance tester is just a variation of the emission tester with its implications, where a proportional AC voltage is applied to each electrode. This tester exists thanks to Jackson mainly to avoid infringing the patents of the mutual conductance tester held by Hickok, but obviously do not provide the same measurements.
[edit] References
- ^ Know your Tube and Transistor Testers, Robert G. Middleton
[edit] External links
[1] The idiot's guide to tube testers