I can not but rejoice in the revival of interest in tube electronics. However, there is something to ponder!

In one of the comments, I once wrote that "the third generation of electronic engineers who are not hit by anode voltage is already growing." Several recent publications with designs on electronic tubes have only strengthened me in this confidence.

I started back in those days when lamp constructions were not exotic, and the first thing that senior comrades taught young hams was how to safely carry out work under voltage. I want to share these “life hacks for geeks” in a publication.

Electric current is dangerous!

Everyone knows that electric current is dangerous. Caring parents insert special plugs into sockets and tell their unreasonable children that nothing can be put into the socket. Caring employers give employees safety briefings.

At the same time, people continue to die from electric shock!

As a rule, people fearlessly touch conductive circuits that they consider to be de-energized. However, a person does not have sense organs to determine the presence of electrical voltage at a distance. Touching live circuits can lead to death!

Briefly, but essentially, the basic rules of electrical safety in amateur practice are outlined in the article “Caution! Electric current ”- Radio No. 8, 1983, p. 55.

In 1983, designing with electronic tubes was no longer so relevant for young radio amateurs, so I will analyze some of the nuances of safe work with lamp structures in more detail.

Be sure to remove the plug from the outlet

Any installation work should be carried out only on de-energized equipment! To do this, the design must include a power switch with hard-locked positions and a power indicator.

The best practice was always not to rely on the switch, but to unplug the power cord from the outlet, i.e. provide "visible break of power supply circuits" of a design.

Also, be sure to remove the plug from the outlet when replacing the mains fuses. Of course, there are designs of safety pads that allow you to change fuses “on the go”, but if the spare fuse “flashes” right when you replace it, it will not have a positive effect on the body.

Capacitors must be discharged.

After the design is de-energized, it is necessary to wait for the discharge of capacitors!

It was considered best practice to discharge the capacitors of the smoothing filter of the anode voltage source through a resistor connected in parallel to the filter output. The resistor value was selected so that a current of the order of 1 mA flowed through it. To make sure that no charge was left on the filter capacitors, a voltage was measured on this resistor.

Capacitors are also dangerous because they can explode. To reduce the risk, follow the rules:

the rated voltage of the capacitor (especially in power circuits) should be 1.5 - 2.0 times higher than the current voltage of the circuit;
it is strictly forbidden to include polar capacitors in a different polarity, and therefore, to use them in alternating current circuits;
the condenser housing must not be damaged, swollen or leaking.

Eyes must be protected

Work on structures on lamps must be carried out with safety glasses! Safety glasses are easier to change than buying spare eyes.

I already mentioned exploding fuses and capacitors. I will supplement with melted ballons of lamps and fragments of resistors flying apart in different directions and molten drops of metal from conductors during avalanche-like processes in the lamp.

You can, of course, think that protection is not needed, but Murphy’s law is harsh, and the fried rooster does not sleep!

Insulation must be holistic

Not every design starts working right after assembly. When debugging, you have to climb into it with probes and screwdrivers, i.e. there is always a risk of voltage or circuit.

Struggle with this insulation of current-carrying circuits. Hook-up wires should have reliable integral insulation. Contacts must be protected against contact by insulating tubes.

It is advisable to isolate the points where you need to measure voltage or look at the waveform during debugging, so it is advisable to insulate with a PVC tube so that the tube is gently moved from the contact for the duration of debugging, and then returned to it. With shrink, it just won't work.

One-handed operation

There is a joke that a real electrician never eats with a fork and a knife, so as not to touch the conductive surface with his second hand.

The best practice when measuring was always to fix one probe of the device with a crocodile clip at one measurement point, place the device on a flat surface in a convenient and safe place, take the second probe of the device in your hand and take measurements with your other hand behind your back. In front of his eyes are safety glasses, of course.

On self-excitation in lamp equipment

Electronic lamp circuits are prone to self-excitation. Self-excitation can lead to a breakdown of the lamp, sometimes with "special effects", leading to the replacement of goggles.

They struggle with self-excitation, shortening signal circuits to a minimum and connecting the outputs of elements connected to a common wire to one point with a "star".

It is best practice to mount circuit elements directly onto the contacts of the lamp panels. They try to make the chains between the cascades as short as possible and arrange them so that spurious feedback does not occur.

The connection to the common wire by the "star" is also caused by the prevention of spurious feedback by flows through the metal chassis.

About transformerless power supply

No attempt to save on galvanic isolation from the network justifies itself! If you want to save money, find the power supply from the tube-semiconductor TV and change the capacitors in it. Get the glow voltage of ~ 6.3 V, the anode +360 V, the negative voltage for the bias circuits, and the power supply for transistors +30 V.

In short, you will be happy, but there will be no problems with the “phase” induced on the chassis.

About working grounding

Working grounding has a fundamental difference from protective grounding in that it serves to ensure the normal operation of the electrical installation.

An example of a circuit that requires a working ground can be a radio transmitter. A special case of a radio transmitter can be considered a Tesla transformer. Working grounding in such schemes is used as the second arm of the transmitting antenna, i.e. power is supplied to the working earth circuit!

In this regard, it is definitely not worth using heating pipes, water supply and gas pipes as a working ground:

the result of power transmission through a gas pipe may be an explosion of domestic gas;
voltage will be induced on the heating and water supply pipes and the water circulating through them, and, as I have already said, people fearlessly touch the conductive circuits that they consider to be de-energized ... In cases where, due to the lack of high-quality galvanic isolation with "transformerless power", such here is the "working grounding" gets the "phase", the chances of residents to survive are rapidly falling.

Instead of a conclusion

I can not but rejoice in the revival of interest in tube electronics. I really hope that my experience set forth in the article will help neophytes experience the joy of technical creativity. And I also really hope that following the simple recommendations set forth in the article, no one will suffer from their passion for lamp technology.

73! de RD9F

Warm, tube and very dangerous