CLOCK-UNIT, GMT 34

ELECTRICAL CLOCKS - PULSE TYPE
Clock Unit, GMT 34

1. General
 Clock Unit, GMT 34 is used to distribute pulses from a master clock (Clock No. 36) to telephone apparatus and clock systems.  It should be provided at offices where 30 second clock pulses and one or more of the following facilities are required:-

1. Pulses for the operation of 1 second clocks

2. 1 second, 6 second or 30 second pulses for telephone apparatus.

The unit is wired to Diagram GMT34 and the apparatus layout is shown on Drawing No. 61080. Installation details are given in B3301.

2. Description
The unit is wired for a maximum of eighty 30 second pulse clocks.  It is fitted initially with apparatus to feed pulses to:-

1. Twenty 30 second pulse clocks, i.e. two circuits of 10 clocks each (relay AP, Diagram GMT 34).

2. Ten 1 second clocks (contact BR2).

3. Telephone switching apparatus requiring 1, 6 or 30 second pulses (contacts BR1, CR1, CR2 and DR1).

A battery jack for a headlamp is provided on the unit.  Where more than one unit is connected to a master clock the additional battery jacks, if required, should be wired in parallel with that in the original unit.

3. Additional apparatus
If the unit is required to drive more than twenty 30 second pulse clocks, the additional apparatus (see Diagram GMT34) should be requisitioned separately and fitted locally.  The unit is equipped for 50 volt working but it can be used on other voltages by changing resistors R2 and R3.

4. Accommodation
The unit is designed for wall mounting in a horizontal position, and should be located close to the master clock for convenience in wiring and maintenance.

Warning
With the change from GMT34 to GMT34/1, the polarity of the clock circuits was reversed.  Previously, they had all gone to a common earth, but this was changed to a common battery.

Introduced circa 1955.

• Clock No. 36 - GMT32

• Clock No. 36 Mark 4 - GMT39/0

• Clock No. 36 Mark 5 - GMT39/1

• Clock No. 36 Mark 6 - GMT39/2

• Clock No. 36 Time Distribution using GMT34 - GMT34/0 and GMT34/1

• Clock No. 36 Time Distribution using GMT35 - GMT35/0 and GMT35/1

Drawings

• Clock Unit GMT 34 (Marks 2 and 3) - P/T 75 and P/T 76

Pictures

GMT 34 showing lid with thumbscrew cover retainers

Plan view of unit

View showing internal components.  The components in the lower central part of the picture have been added after the unit was installed - see paragraph 3.

View showing connection strip

Last revised: November 21, 2023