Tube tester

Examples of modern testers include the Amplitrex AT1000, the Space-Tech Lab AudioTubeTester, 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.

Next in complexity 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.

The main difference is the use of ‘proportional AC voltages’ in place of applying the current directly to the grids and plate.

A tester of this type applies DC voltage to the tube being tested, and datasheet values are verified under real conditions.

Some parametric testers apply AC voltage to the tube being tested, with verification under conditions which simulate DC operation.

The mutual conductance tester tests the tube dynamically by applying bias and an AC voltage to the control grid, and measuring the current obtained on the plate, while maintaining the correct DC voltages on the plate and screen grid.

At that time, tubes in consumer devices were installed in sockets and were easily replaceable, except for the CRT in televisions.