Date of Design The Type 48 Series {Types 48, 48C, 48X and 48Y} were the products of the 1933 period - this was widely fitted in our "big hitters" during and after WW2.  An example only of those ships fitted with or earmarked to be fitted with are shown below:-
Type 48: [BASIC SET] - Liverpool, Manchester, Newcastle, Sheffield, Southampton, Sydney, Signal School Portsmouth  etc.
Type 47C:  Ark Royal, Belfast, Dido, Devonshire, Fiji, London, Forth, Mauritius, Queen Elizabeth, Renown, Signal School Portsmouth, Sirius, Valiant, Warspite etc
Type 48X: Dorsetshire [torpedoed the Bismarck] and was Commanded by Captain Martin, a former Gunner [Warrant Officer].
Type 48Y: Leander
Frequency Range
Transmitter 2S L/F Low Power 2S H/F Spark Transmitter 6D
Master Controlled Self Excited Master Controlled Self Excited
Frequency range 60-500 kc/s 60-500 kc/s 60-500 kc/s 3000-16500 kc/s 3100-15500 kc/s 70-500 kc/s 60-500 kc/s
Power supply 20kW  Alternator 20kW  Alternator 11kW Alternator 20kW  Alternator 20kW  Alternator 20kW  Alternator 20V Battery
Filament supply 11kW  Alternator 11kW  Alternator 11kW  Alternator 11kW  Alternator 11kW  Alternator -  -
Valves used 7 4 3 7 4 - -
Wave form CW & ICW CW & ICW CW & ICW  CW & ICW CW & ICW  Spark Spark
Associated wavemeter G56, G57  

G56, G57


G56, G57  G57 G57 G56, G57  G56, G57 
Approximate range in miles 1500 1500 100 World wide at times World wide at times 150 50
Date of design 1933 1933 1933 1933 1933 1930 1928
Power Supply See above to Frequency Range. The power board consists of two panels [upper and lower] which are secured to the transmitting panels.

Type of Set See above to Frequency Range.
Wave Form See above to Frequency Range.
Method of Producing Oscillations Self
Where used/fitted.

Type 48 series is the main transmitting set for heavy ships and cruisers and replaces the Type 36S. It is a high power set.

The set has four power boards which carry the necessary switches, fuses and instruments for the distribution of power to the set and W/T office. The transmitting circuits are carried in eight main valve panels which face the power boards and the rectifying and smoothing panels which are fitted in a convenient position inside the safety cage.  A small panel containing the H/F neutralised condensers, etc, is secured to  the back of the H/F main transmitting panel. The switches necessary for the control of the set are assembled in "Board 2S Controlling" which is mounted on a stand and fitted in the CRR [central receiving room] {note, the silent cabinet, used from the very earliest of days -see PRE WW1 FILES - is no longer fitted/used}.

This was the first set with a MASTER OSCILLATOR which had a single controlling valve and was the primary means of producing the oscillations - All the Components of the H/F Master Circuit are enclosed in an earthed copper screening box supported by springs in Panel 3S H/F Master.  The set  was also fitted with the then conventional [all previous sets] Self Excitation which was used when and if the Master Oscillator became un-useable. The waveform characteristics were shown as follows:-

Waveform Method of producing oscillations Nature of Circuit Grid Excitation Feed Aerial Excitation High oscillating potential electrode
Master Main Master Main Master Main

TYPE 48 Transmitter 3S L/F Master Control

CW or ICW Master Controlled Tuned circuit between anode & grid Tuned circuit between anode & filament Direct inductive Direct inductive from Master circuit Parallel Parallel Direct inductive Anode
TYPE 48 Transmitter 3S L/F Self Excited - standby for Master failure
CW or ICW Self Tuned circuit between anode & filament Capacitive Parallel Direct Inductive Anode
TYPE 48 Transmitter 3S H/F Master Control
CW or ICW Master Controlled Tuned circuit between anode and grid Tune circuit between anodes of main valves connected in push-pull Direct inductive Direct capacitive from Master circuit Series Parallel Mutual inductive Anode
TYPE 48 Transmitter 3S H/F Self Excited - standby for Master failure
CW or ICW Self Valves in push-pull tuned circuit between anodes and grids Direct inductive Parallel Mutual inductive Anode
TYPE 48 L/F Low Power
CW or ICW Self Tune circuit between anode and grid Direct inductive Parallel Direct Anode

The L/F Master circuit is disconnected from the main transmitter and used as the Low Power transmitter, connected direct to the aerial via a contact arm of the L/F circuits change over switch [COS]. See this file which simply shows the working of the Type 48 Low Power Set 48 low power.pdf.

This transmitter was capable of high speed Morse transmission and used Grid Signalling to achieve this.  This necessitated HT to the main amplifying and master circuit valves being made continuously. Put simply, when the Morse is being sent [key down = 'marking' or mark condition] the aerial absorbs the resultant 'oscillatory signal' but when the transmitter is 'spacing' [key up = nothing being sent] the valves themselves were designed to absorb the 'non-oscillating' condition of the transmitter. The following file shows how the transmitter coped with the 'marking' and 'spacing' conditions 48 GRID SIGNALLING AND ABSORBING.pdf.  In direct association with high speed transmission, came the need to self-check for the accuracy of transmission.  This is the simple diagram to control that event, and note the undulator, a high speed automatic Morse keyer/sender - 48 self monitoring.pdf.

Associated Wavemeter See above to Frequency Range.
Small Schematic

See this file for the complete Type 48 48 OVERALL SCHEMATIC.pdf

Look here to see the all important big ship aerial circuits and the protection of receivers sited in offices remote from the main W/T office which use the aerials 48 aerial ccts and aerial protection ccts.pdf.

This is one of the aerial systems for the Type 48 48 AERIAL SYSTEM.pdf

The auxiliary switching circuits which we can liken to the traffic lights of a large and complex transmitter system.  These include the transmitter type used, its emission, its aerial, its protection circuits [equipment and personnel] etc 48 auxiliary switching circuits.pdf.

Type 3S H/F Master Control Equivalent Circuit

Type 3S L/F Self Excited [ignore the text in this case]


Above and below the Type 48 big ships transmitter system

2S Controlling outfit