WARNING:

This tester is a highly professional instrument, not intended for amateur use. Do not use it at the level of a multi meter, or for learning by doing. Do only what you know is right.

Legally, we must say, the purpose of these cards is only to show you, what we use in our own company, and there is no other purpose. Please understand the legal reasons why we have to say this.

We only can say, we use these cards ourself here, and they work good to the best of our knowledge. They are experimental products by definition, because there is no guideline from the tube tester manufacturer, how to make those cards. Do not buy those cards, if you expect something else.

It is definitely needed, to read and understood the manufacturers manual belonging to this tester. Moreover, the user must be qualified to work with high voltage, because warnings can not replace experience and knowledge.

These safety rules will not replace the manufacturer's recommendations, please regard this additional, very important information when using the L3-3.

1. The tester has a ground plug (banana plug) at the deck plate, and by default works with the whole tester not grounded. Given the tester has a good quality mains transformer, this is a safe option. However there will be some capacitive current flowing, which sometimes can be felt, and also you are not protected against any kind of internal failure. Given the wiring is old, and given the tester's history is unknown, personally I do not rely on this, and I ground the tester, by using a grounded mains cable. I attach live and neutral to the two wire mains plug. Then, from inside that plug, I let a ground wire come out. On that ground wire I attach a banana plug, which fits into the ground plug in the deck plate.
2. If the tester would test smaller rectifiers in parametric mode (Forward Voltage Test) the forward voltage and plate current is not dangerous. Yet at some of the the switch board plugs, very high voltages are present still, even when the card is programmed for low voltage.
3. However in the rectifier POWER MODE, a very high voltage must be applied to the switch panel, to the plugs, and to the tube anodes as well. Also, at many of the unused sockets, there are pins which have this high voltage as well applied to it. This can not be avoided, because all sockets are connected in parallel.
4. On the shafts of the pins of the switch board, can be high AC or DC voltage to ground. This depends on the cards and the settings of the knobs. Sometimes it is very little, but sometimes it can be up to 550V to ground. So it is life threatening dangerous to lean with one hand on the metal handle, and with your other hand touch by mistake the pins of an empty socket, or the metal part of the plugs. It is generally better, not lean on the tester with one hand, and operate it with one hand only. Like this an electric shock, if it happens, will probably not go through the body.
5. If the glass of a tube breaks while you pull it out, specially with rectifier power tests, there is 1100 Volts AC from anode to anode. (so 1100 Volts center tapped, for 2x 550V). You can be seriously injured when that happens. Worst case you are dead, but you can also very badly burn your hand. The hand muscles will close violently, because of the electric stimulation, and the electric current may cause a third degree burn.
6. For this reason, officially you should always switch off the tester before inserting or unplugging tubes or card pins. Specially with rectifiers in the power testing mode, this rule should be strictly followed.

Sorry for the many warnings.... but it is better to say it clearly.