I'm telling you about the design of Soviet resistors MLT-2 (9 photos)

Hello everyone. Today I would like to talk to you about Soviet radio components. Specifically, we will talk today about MLT-2 resistors.





Appearance of four MLT-2 grandfathers of different denominations

As you all know, resistors in electrical circuits are necessary for solving various problems: current limitation, energy absorption, etc., and their main characteristics are: their resistance value and the power for which they are designed.

The MLT-2 resistors are a classic example of a Soviet resistor and can be found in almost any equipment of that time. The abbreviation MLT stands for Metal-Film Varnished Heat-Resistant. The number 2 means the power of the resistor in Watts that it can dissipate. That is, the MLT-2 is designed for 2W. Also on the resistor body there is a marking indicating its nominal resistance.



Resistor MLT-2 33 kOhm 2W

In general, the marking of the resistor shown in the photo is deciphered as follows: Metal-film varnished heat-resistant resistor with a nominal value of 33 kOhm, capable of dissipating power up to 2W.

Let's look at the design of this resistor. In general, it is shown in the photo below.





The design of the MLT-2 resistor

The entire resistor is covered with varnish paint, which has electrical insulating properties. It is usually red-brown in color.



And this hard worker was literally "roasted" at work

Please note that if the resistor heats up for a long time during its operation, this paint may change its color.



I scraped off the paint from the resistor and exposed its copper nickel-plated cup

If you scrape off this paint with a sharp object, it easily comes off the resistor and exposes the parts located underneath. So, on the sides of the resistor there are copper cups with a nickel coating, to which copper tinned leads are soldered.



If you scrape hard on the nickel-plated coating, you can reach the copper in the cups

Depending on the year of manufacture, these terminals may be silver-plated. There is no point in collecting these terminals for the sake of extracting silver, you will spend more money on reagents, since the silver content in one MLT-2 resistor is only about 0.006 g. But this fact should be kept in mind by financially responsible persons who are responsible in the organization for old equipment that is on the accounting books and in which these resistors may be found. When writing off such equipment, all these resistors will have to be either extracted and handed over separately or transferred to a specialized organization. The presence of silver in these resistors can be clarified in the form for the equipment in which they are contained. You can visually determine the presence of silver in the terminals by their blackening over time, and such contacts will be worse soldered than ordinary copper tinned terminals.



The conductive resistive film has been exposed

If you continue scraping the paint off the resistor tanks, you can see that a ceramic tube is clamped between two copper cups, on which a resistive film is applied along its surface. It is this film that is responsible for the resistance rating of the resistor. The spirals that you are leading in the photo are cut on a ceramic base. By changing the material of this film and the number of turns of these spirals cut into ceramics, the final resistance of this resistor is adjusted.



Bitten MLT-2 into two parts



MLT-2 in section

If you split the resistor in half, you can see that the main volume of the resistor is occupied by ceramics, and the resistive film is very, very thin.

For today, that's all I wanted to tell you about MLT-2 resistors, if you have any questions, write to me, I'll be glad to answer them.