The EML 20 series must be tested at higher anode voltage as is possible by default with the L3-3. Maximum is 300Volt for the meter. However it should be possible to adjust for higher anode voltage, as long as you do not pull high current, and if the L3-3 tubes itself are good condition. To measure the voltage, connect a voltmeter between the deck ground banana connector, and connector A1 (which is located between sockets 1 and 2). The voltage measured is above 400Volts, so use appropriate test cables and respect the high voltage.

Note1: With this card, the meter inside the tester is switched off for anode voltage measurements. So you can only use the external voltmeter.

Note2: In general, and also here: If the measurent produces things which "can not be", switch off the tester measurement immediately, and find with the tester off, what error was made.

Procedure to check a new tube:

1. At this point, the tube is not inserted.
2. Plug in the card and connect the external voltmeter
3. Adjust the anode voltage and grid voltage, using data of the Emission Labs tube box. If the box is missing, use data of the card.
4. When the grid voltage Ug1 could be adjusted successfully, this was only for initial control. After this, increase Ug1 to the maximum value.
5. Set heater voltage to the minimum. (Both knobs counterclockwise). Insert the tube, and adjust the heater to 5V. Look inside the tube, for control.
6. Check again the anode voltage, and now adjust the grid voltage such that the plate current will flow, as marked "ideal" on the card. If you still have the tube box, and plate current on the box is another, use box data.
7. Read the grid voltage from the tester. This should be the same as on the tube box, when the tube is new.
8. Do the transconductance measurement. This should be the same as on the tube box, when the tube is new.

Procedure to check a used tube::

1. This is done best with the data of the original tube box.
2. First use card data. Set for ideal plate current, and test Gm. The "green zone" indicates already if tube is good.
3. Continue now with the box data.
4. Set anode voltage and grid voltage as as on the tube box.
5. Measure Anode current. For a new tube, this should be 100%.
6. A used tube should be above 70% and it is good.
7. From 60...70% the tube will probably work too
8. Below 40% the tube will probably fail.

If the tube is testing around 70%

1. The question may be for remaining life.
2. Increase heater voltage to 5.5Volts, but limit this kind of testing to 5 Minutes.
3. If this gives a significant improvement of plate current, this means little life is left.
4. If this gives only a small improvement, remaining life is perhaps a lot.
5. If a tube is testing very low, it is a good idea, to check the heater voltage of the working amplifier, with this tube inserted. It must be exactly 5V.