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← 300 A
Cold War
300 AB   Irak
200W short wave transmitter

The 300-AB was a 200W long-range short-wave (SW) spy radio transmitter for the 10-18 MHz frequency range, developed in Czechoslovakia in 1961 by Správa 6 1 for use in international espionage outside Europe, by the secret state police (StB) and by Správa 1 (espionage). It consists of the 300-A Transmitter, the 300-B Power Amplifier and the 300-C Antenna Tuner. It was first used in 1961 in Congo and was later also used from 1965-1968 in Kurdistan (North-Iraque).

The 300-AB was developed to overcome communication problems between Congo and Czechoslovakia. The bare 300-A transmitter, with its 20W power output, wasn't powerful enough, and even the Kongo 50W transmitter, which was introduced a year earlier in 1960, was not always strong enough to reach Control.

The image on the right shows the complete setup, with the transmitter at the bottom right and the power amplifier on top of it. The device at the left is the 300-C heavy duty antenna tuner that came with the 300-B Power Amplifier.
300-A transmitter, 300-B PA and 300-C antenna tuner

The 300B Power Amplifier is extremely heavy as it also contains a mains power supply unit (PSU). When installed on top of the transmitter, the mains plug should be inserted into the socket at the right side of the transmitter. This 220V AC socket supplies the fully filtered mains voltage. The antenna output of the Transmitter is connected to the input at the left side of the Amplifier.

The 300-AB was probably produced in small quantities, as the units have no project number and no engraved text on their front panels. Instead, the text and the model number are applied by means of Dymo labels. No documentation and/or circuit diagram is available at the moment. The unit was used in Congo in 1961 and in Kurdistan (a.k.a. North-Iraque) from 1965 to 1968.

  1. Správa 6 refers to Government Department 6: Communication Technology.

300B amplifier on top of 300A transmitter 300-A transmitter, 300-B PA and 300-C antenna tuner 300-A transmitter (20W) 300-B Power Amplifier (200W) Front panel Tuning the PA grid Rear view of the 300C antenna tuner
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300B amplifier on top of 300A transmitter
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300-A transmitter, 300-B PA and 300-C antenna tuner
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300-A transmitter (20W)
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300-B Power Amplifier (200W)
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Front panel
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Tuning the PA grid
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Rear view of the 300C antenna tuner

The diagram below shows the controls and connections on the 300B Power Amplifier. The black lead at the right should be connected to the 220V outlet on the right side of the transmitter. The output of the transmitter goes to the input of the amplifier at the left, via a short coaxial cable. The antenna is connected, via the 300C antenna tuner, to the output socket at the rear.

The amplifier should be placed on top of the transmitter, where two wooden rigs ensure sufficient cooling for both devices. Like the transmitter, the amplifier is switched on in two stages: (1) the LT voltage for the filaments and, once they are heated, (2) the HT voltage. The large knobs are for tuning the grid and plate of the PA valve for a maximum reading of the corresponding meters.

The construction of the amplifier is very simple. The right half contains the large and heave transformer, whilst the left half contains the actual amplifier with the QE08/200 valve at its heart. Access to the PA valve is possible via a removable panel at the rear, fixed with 4 screws.

The image on the right shows the PA, as seen from the rear of the device. At the left are he tuning capacitor and the tuning coil. The large PA valve (QE08/200) is at the top right. The PL519 output socket is at the top left.
The 200W QE08/200 valve

Access from the rear The 200W QE08/200 valve The 200W QE08/200 valve
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Access from the rear
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The 200W QE08/200 valve
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The 200W QE08/200 valve

Valves   tubes
  • QE08/200
    200 Power Amplifier
  • 300-A4
    Transmitter 20W
  • 300-B5
    Power Amplifier 200W
  • 300-C3
    Antenna tuner for 300-B
The 300 A and the 300 AB were used in the following countries:

  • Angola
    1961 (300A)
  • Congo
    1961 (300AB)
  • Kurdistan
    1965-1968 (300AB)
  1. Anonymous, 300-AB transmitter and amplifier - THANKS!
    Devices kindly donated by anonymous former user. July 2015.
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Crypto Museum. Created: Wednesday 19 August 2015. Last changed: Wednesday, 28 February 2018 - 22:43 CET.
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