With this card, you can test the firing voltage of the Regulator tubes and Staviliser tubes.

The procedure using this card is: Set the anode below the ignition voltage. Then slowly ramp up, until the tube fires. Firing will be a relative high current. Regulate down the current, within normal range. Now let the tube warm up, and then test it's condition.ts.

Though they apparently work the same, Voltage reference tubes, and stabilizer tubes have another purpose.

Voltage reference tubes gives a stabile voltage over a long time, but the specified stability and lifetime (for the stability) will only be achieved a the specified current. To test a stabilizer tube, check if the voltage is as specified, within the allowed current limits. Outside these limits, testing is not relevant.

Stabilizer tubes have a specified current range, over which it will produce a stabile voltage. So the voltage itself is not as extremely precise as with a stabilizer tube, but for that you can change the current range. To tes a voltage reference tube, set it for the normal current, and check if the voltage is correct.

Note, with each, they DO SEEM to work, when reversed, or if operated outside the specified current range, they seem to work, but stability is not good.

New tubes will an amazing precision, buz depending on brand and make, differences can appear. The most amazing are the GR150 tubes, as made specially fot the Funke tube testers.

Worn out tubes are characterized by not so good regulation any more. Though they often still work for the rest of it. This seems to have to to with a change of the gas inside the tube. Some tubes contain small traces of special gas, which seems to get inactive after long use. So what is left then is the normal gas. Such a tube still works, but precision is less. Also the burning color changes.

Good tube	worn out tube