10 kW H.F Broadcasting Transmitter Type B 6120

photo Marconi B 6120 THIS transmitter is of particular interest where economic considerations necessitate the minimum of outlay and running costs, without sacrificing quality of performance and dependability of service.


Air cooling is employed throughout.

Xenon-filled rectifiers are used, capable of operation over a wide temperature range and requiring no conditioning.

Miniature circuit breakers are incorporated which largely avoid the necessity for fuses and contactors.

Full protection of equipment is ensured by magnetic and thermal overload relays.

Personnel are protected from contact with high voltages by a key-type interlock system.

Installation costs are reduced to an absolute minimum. No floor ducts for cooling or cabling are required.

Efficiency is of the order of 50%, and thus running costs are extremely low.


The transmitter cabinet is built up from four standard units 7 ft (213cm) in height and 3 ft 9 in. (114cm) deep. The whole cabinet as sembly occupies only 37.5 sq. ft (86 sq. dm) of floor space, and is completely self-contained including cooling fans and high-power components.


Drive stages. The Drive Unit Type (HD 26) normally employed with this transmitter can be internally mounted.

A harmonic generator unit follows the crystal drive unit, to produce a frequency between 3.2 and 18 Mc/s which is passed to the r.f amplifiers.

R.F stages. There are three stages of r.f amplification. The first is a single tetrode stage; the second employs two tetrodes and is capacitance-coupled from its anode circuit to the grid of the final stage which uses a neutralized triode. The final stage has a balanced output circuit which is coupled into the outgoing feeder. This is a 600-ohm balanced pair.

Modulation stages. A system of high-level class B modulation is employed. Three a.f amplification stages are used to amplify the input signal to a level sufficient to drive the main modulator valves. An input signal of 0 dBm is sufficient to produce full modulation.

The modulator, which uses two triodes, is fed from the a.f amplification chain via a cathode follower stage.

Power supplies. The main h.t supply is obtained from six xenon-filled rectifier valves which require no conditioning. a.c valve heating is employed.

The control and protection circuits are simplified by the use of circuit breakers in place of fuses and contactors.

Power output 10 kW unmodulated carrier to aerial feeder
Frequency range Broadcasting bands between 3.2 and 18 Mc/s
Frequency stability To within ±10 parts in 106 over a temperature range of ±15°C
Modulation High-level, Class B
Scintillation Not greater than 1 c/s up to 90% modulation
R.F harmonics Less than 200 mW
A.F input 1 mW into 600 ohm for 100% tone modulation. (An attenuator is fitted to cater for inputs up to +12 dBm in 1 dB steps.)
A.F response Level within ±1.5 dB from 50 to 7500 c/s
A.F distortion Less than 3% up to 90% modulation (50 to 7500 c/s)
Output impedance 600 ohm balanced
Noise level Below 60 dB relative to 100% modulation, unweighted
Ambient temperature +45°C max.
Power supply 380-440 V (±5%) 50-60 c/s (±2%) three-phase a.c.
Power consumption 20 kV unmodulated.
22 kW at 30% modulation (1000 c/s)
32 kW at 100% modulation (1000 c/s)
Power factor 0.9 at full output power
Dimensions Height 7 ft (213 cm)
Width 10 ft (305 cm)
Depth 3 ft 9 in. (114 cm)
Weight (approx.) 2 tons (2032 kg)
Specifications may change without notice

RF stages AF stages and modulator
Number Type Number Type
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