Tube tester: Difference between revisions

Revision as of 21:18, 10 April 2014

Revision as of 05:46, 1 July 2014

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==Types of tube testers==

===Modern testers===

These perform a multitude of the below tests and are fully automated. Examples of modern testers include the Amplitrex AT1000, the Maxi pre-amp tester and the maxi-matcher (power tubes only) by maxi test and the new and somewhat more primitive DIVO VT1000 by Orange Amplification. While the AT1000 and the Maxi-test brand testers offer precise measurements of transconductance/Gm and emissions/iP at full or near full voltages the Orange tester offers a very simple numerical quality scale.

===Filament continuity tester===

The simplest one is the ''filament continuity tester'', usually with a neon lamp connected in series with the filament/heater and a current limiting resistance fed directly by the mains. There is therefore no need to select the appropriate filament voltage for the particular tube under test, but this equipment will not identify tubes that may be faulty in other (more likely) ways, nor indicate any degree of wear. The same checks can be made with a cheap [[multimeter]]'s resistance test.

===Tube checker===

The second-simplest of all tube testers after filament continuity testing. Tubes are used as low power rectifier, with all elements other than filament connections connected together as the anode, at a fraction of its normal emission. By mistake referred to sometimes as Emission Tester sometimesbecause they are a crude measure of emission in directly-heated types (but a measure of unwanted heater-cathode leakage in indirectly-heated types). Switches will need to select the correct filament voltage and pins.

===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 [[Battery_(vacuum_tube)#B_battery|B+ voltage]], feeding the filament with the correct voltage, and an ammeter in series with either the plate or the cathode. This effectively measures [[Thermionic emission|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. Switches will need to select the correct filament voltage plus which pins belong to the filament and cathode(s).

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.<ref>Know your Tube and Transistor Testers, Robert G. Middleton</ref>

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* 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

* grids will be forward biased to some extent - some fine control grid wires are limited in their ability to withstand this

* the amount of current that should be considered "100%" has to be known and documented for each tube type (and will be different for different emission test circuit details)

The ''advantage'' of an Emission Tester is,: from all types of tube testers available, it gives the most reliable warning for tube wear out. If Emission is at 70%, transconductance can be at 90% still, and gain at 100%. Best and most popular Version used by the German army, is the Funke W19.

The ''disadvantage'' of an Emission Tester is,: it can test a good tube as bad, and a bad tube as good, because other qualities of the tube are ignored by this type of Tube Tester. In America, Drug Store Tube Testers were very popular, and were intended to make money for their proprietors. Many Tubes were sold that were not needed based on the criteria of Low Emission. A Tube with Low Emission will work perfectly fine in most circuits, and should not be replaced by that indication alone, unless it measures much lower than specified or if it indicates a short.

===Short circuit test===

Usually, ''emission testers'' and better testers also 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 pairs of electrodes.

===Parametrical tester, DC Type===

This tester Applies DC voltage to the Tube under Test, and datasheet values are verified under real conditions. Good examples are '''Funke W20''' and '''Neuberger RPG375'''.

===Parametrical tester, AC Type===