MARCONI SWB 18

GENERAL DESCRIPTION

THE INTERMEDIATE AMPLIFIER

photo Marconi SWB 18

The Intermediate Amplifier is a high efficiency two stage Class C push-pull circuit which magnifies the output of 100-120 watts from the Drive Amplifier to approximately 12 kW.

A notable feature of the design is the entire absence of long conductors carrying high frequency currents.

This is rendered possible by the adoption of a novel design of valve mounting and condenser assembly in which the valve jackets form an integral part of the anode tuning condenser.

This form of mounting is extremely rigid and compact and provides that high degree of electrical and mechanical stability so essential for high fidelity broadcasting.

The transmitter is designed to operate on any selected wavelength between 13.5 and 80 metres (22,222 - 3,750 kc.). Change of wavelength is by means of an ingenious design of interchangeable trucks carrying pre-set high frequency tuning circuits.

All contacts between the truck and the stationary components in the transmitter are self-aligning and cleaning and are of such ample dimensions as to prevent any undue heating. Special self-locking devices prevent any possibility of the contacts being only partly engaged, thus eliminating any trouble due to faulty connections.

THE MODULATED AMPLIFIER

The modulated Amplifier is a single stage Class C push-pull circuit which magnifies the 12 kW output of the Intermediate Stage to approximately 100 kW.

The stage consists of two water-cooled valves connected in a neutralised capacity bridge circuit.

Similar to the Intermediate Amplifier there is a complete absence of long conductors carrying high frequency currents, the same type of assembly for valves and condenser being used.

One hand wheel operating through a Lockheed hydraulic system controls the main tuning condenser, balancing condensers and output coupling, selection of any of the three adjustments being accomplished by small levers immediately beneath the hand wheel.

As in the Intermediate Amplifier chnge of wavelength is effected by means of interchangeable H.F. circuit trucks.

Change from one wavelength to another wavelength, for which the H.F. circuits have previously been adjusted, can be carried out by one man in the short period of 10 minutes between power "off" and "on."

THE MODULATOR

The Modulator is operated in a Class B condition and comprises a four stage distortionless amplifier, using two valves only, connected in push-pull in each stage.

Careful design of the stages ensures distortionless operation and the use of the Class B circuit provides high efficiency operation and consequently a considerable saving of input power.

CONTROL AND MONITORING DESK

Complete monitoring and control of all power supplies are centralised at the Control Table.

Switches operate the remote starters for the various motor-generators.

Voltage regulation is performed by motor-driven field regulators operated by conveniently placed controls on the table.

Indicator Lamps associated with the mechanical and electrical interlock safety system give a visual indication whether relays and circuit breakers have closed after any interruption of the interlock system such, for instance, as a change of wavelength.

TUBE COMPLEMENT
RF stages		AF stages and modulator
Number	Type	Number	Type
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THIS TYPE OF TRANSMITTER IS INSTALLED IN THE FOLLOWING COUNTRIES
	ITU	Country	ITU	Country
	MLA	MALAYSIA	G	UNITED KINGDOM