Russian transceiver 10 PT 12

In WW2, the Russian army, as well known, took a big part in fighting the German Nazis. They too, used a large amount of different radio systems for their communication.

One of these radio systems was the 10 PT 12 or 10 PT 26. The 10 PT 12 was mainly used in armoured car vehicles, while the 10 PT 26 was used in their famous tanks, like the T-34.

But just at about the last part of the war. In the beginning at about 1941/42, most tanks, like the T34 even did not have radio, later only the commander tank did have a transmitter and a receiver, while the other tanks had only a receiver. But at the beginning even no one did have any radio, while the attacking German tanks did have. Signs to the others were given by flag signs? That radio was  a big adventage for the Germans.  It seems, that the Russians suffer big losses, because of lack of communication. But later, at the end of the war, with the help of better communication, these T

-34’s were superior to the German tanks, like Tiger or Panther.

This also not because of their (smaller) guns and armour, they were smaller, but mainly because of their bigger speed. They could change their direction or changing position much faster then the heavy weight and bigger armoured German tanks.  That was the the big difference and was therefore most effective.

About the block diagram circuitry, it is much alike the Brittisch and Canadian Wireless set no 19. This transciever also use a transmitter mixer stage, with 2 signals mixed in it, the BFO on the frequency of the MF and the oscillator stage of the receiver.

The frequency covering of the 10 P(R)T 12 or 26 is 3,75 Mc till about 6.0 Mc. Also 2 crystal channels could be used.

The transmitter had a power of 3 watts on CW and 2 watts on phone. The antenna was mostly a 4 meter whip antenna.

After the war, the radio set was also used by the East German NVA army, also other Eastern Block countries.  So the Tsech army used it. You can see it at the Tsech or German text plates on it.


My experience with the 10 RT 12.

I managed to let the installation work in the 80 meter band.

But the transmitter seemed to be very tricky in use, because of his many unwanted harmonic signals , comming out of it. Also sometimes self-oscillating of the transmitter part occured. Why, I have maybe some explanation for it. See my my explanation below.

The frequency of the signal of the transmitter mixer part is in the receiver, is only pre tuned by one tuned  resonance  coil. ( mixer circuit 305 in the schematic diagram).The receiver needs to be realigned very secure, because this circuit 305 could be easily tuned to a false or  harmonic frequency, also other circuits in the anode circuit of the HF stage of the receiver.

In the transmitter part, there is no effictive pretuning to the working frequency, only  2 HF suppressor coils, which are very broad. Also the coil in the PA output stage, is not exactly in resonance with the working frequency, it only matches the transmitter to the anrtenna.

Because of these HF suppressor coils, the buffer and poweramplifier amplifies almost all frequencies below the 6 Mc or even higher frequencies. So it is most important to fed the transmitter part with a very clean, free of harmonics, signal.

So the only tuning to the correct  frequency to be used, is the correct matching to the antenna lenght. You can see the  the antenna in series with the matching coil in the transmitter part, as a complete resonance circuit, tuned to the working frequency. Otherwise harmonic frequencies become very strong!

You can easily match the wrong signal to the antenna!

I did a very secure alignment of all, spend a lot of time to it, but did not succeed in suppress the harmonics sufficient enough.

But maybe, that was not such a problem at that time. It was “wartime” , the British should say: Nowadays it is much more critical.

So I decided  to use the 10 RT 12, only for receiving signals, not to use the transmitter, untill  I have managed to solve these problems. But I am afraid I have to modify the schematic of the buffer/ amplifier stage to do so. Maybe a tuned circuit in the anode line of the buffer, and a real tank coil in the ande line of the PA? But then the transmitter is not original anymore, I have to think about it.

 The transceiver 10PT12.


 10PT12 012

Left the power supply for 12 volt, in the mid the receiver with crystalbox and right the transmitter.

The receiver 10PT12.


The receiver part, which is in my case, a modified 10 RT 26, the heatercircuit is modified from 26 volt to 12 volt, because the whole system is 12 volt. The receiver containes also a part of the transmitter.  It containes a transmitter mixer stage. In this mixer, 2 signals are mixed to the transmit frequency, eg. the crystal controlled calibration oscillator at 525 Kc( a kind of BFO) and the receiver oscillator. This signal from the mixer is fed through circuit 305 to a connector on the right of the front to the transmitter, to be amplified.

The transmitterpart 10PT12.


The transmitter part. It consist of a power amplifier with buffer amplifier. Also one modulator stage is in it. It is modulated by a carbon microphone element in the tank helmet. You can choose 2 channels, the yellow and the red band section, but in the same overal frequency band.. The 2 knobs are tuning the the antenna matching of the 4 meter whip antenna. So it is easy to switch to a another channel without tuning again.

The rotary transformer, power supply 10 PT12.


The powersupply unit for 12 volt. left up the receiver dynamotor and right up the transmitter dynamotor. In the mid the strange on/off switch. Battery power on receive is 7 ampere, on transmitt 17 ampere!

The crystals of the 10PT12.

The crystals are very different of the western allied types, I never saw it before.

On the picture below, you see 2 crystals. In the internal mid, you see the normal crystal plate.But at the left and right of it, you see a condensor. See also the schematic diagram at the end of this post.

When the operator chooses a red or yellow crystal channel, the main frequency tuning variable condensors are switched off. Now the correct tuning of the receiver oscillator circuit and the HF stage circuit are not correctly tuned anymore.  In this case the condensors in the crystal case are switch by. The value of the capacity is that way, that both stages are tuned correctly on the to be used frequency. So a quick frequency channel change is done without retuning. Technical it is a very beautiful solution.


crystal box

The crystal box with spare crystals just placed on the upper side of the receiver case.

Cover plates.

When once tuned the transciever to the to be used frequency channel, the cover could be placed on the fronts. This to prevent damage to it. When a tank is on the move, many mechanical shocks occure inside the tank or vehicle. The knobs are easily retuned after touching them by accident.

frontcover side onefrontcover  side 2

The frontcover of the receiver. The cover can be fastenend by the 2 knobs on the receiver front.


Here to bee seen the cover mounted on the front of the receiver.

Tuning knobs of the transmitterpart 10 PT12.

transmitter earial tuning

A close up of the tuning knobs with scale of the transmitter part. In the mid, the connection, where the transmitter mixer signal is fed to.

Battery 12 volt 150 Ah.

battery 12 volt 150 Ah

The big battery of 12 volt 150 Ah. It is sure needed, because during transmit, the battery drain is 17 Ampere.

The schematic diagram of the 10PT12.

schematic diagram

The schematic diagram.

Note that the early versions of the 10 P(R)T have small changes in the circuitrycomparing it with the postwar 10RT26.

 The 6k7 valve in the left lower part is the transmitter mixer, with in its anode line the 305 circuit. This circuit is also used during receive as the input circuit for the HF stage.

The valve 6k7 with the crystal, is the calbration oscillator, which can also be used as a BFO for CW or SSB. The crystal frequency is 525 Kc, just like the MF frequency. The 2e valve at the upper left is a penta grid valve, the 6G7.  It function as a self oscillating mixer, eg the oscillator for  the receiver.

Both the BFO frequency and the receiver oscillator are mixed in the transmitter  mixer on transmit. Al tuned circuits need a very well alignment for transmit !!

Posted in Russian_navy_army.

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