POST OFFICE GULSTAD 304 RELAY, 1900's

The Gulstad Relay was invented by K.Gulstad of Copenhagen in 1898

The Relay was used in telegraphy for amplifying the power. The coil is energized by a very small amount of power which activates a contact moving larger locally supplied power.
Post Office Gulstad Relay
This relay is more sensitive to vibrating at high speeds than other P.O. Relays. It achieves this by overcoming delays in movement due to residual magnetism. Up to 200 words per minute is possible using this relay, the average rate of transmission was improved by 50% by fitting these relays on Duplex Systems, see item A0253. Recognised by the letter 'G' or the name itself. Suitable for a single needle telegraph or double plate sounder.
For types of P. O. relays see A0252.

A0238

POST OFICE RELAY 'B' No 14802, 1920's

Relay used in telegraphy acting as a form of amplifier for the signal, sensitive coils moved the contacts which controlled equipment that could be powered locally.

Post Office Standard Relay 'B'

This relay replaced earlier forms known as 'A' having coils of 100 ohms instead of 200 and being shorter in length. Relay 'B' also sometimes having differential coils (two winding on each coil) It can be of the polarised (see item A0239) or non polarised type the polarised version has a magnet and can be neutralised, as in use with the double plate sounder item A0227, provided it has double throw contacts, which means the pole or tongue 'T' is held between M(mark) and S(space) contacts.

The relay shown only has a single throw contact, and is not polarised (no Magnet).

A0278

POST OFFICE RELAY 'B' No 5462, 1920's

Odd version marked as 'B' but more like a 'D' relay, for information on Telegraphy relays see item A0252. it has a single throw contact is non polarised (no magnet) has only one coil, with no other markings.
Resistance 500 ohms.

A0277

POST OFFICE RELAY TYPE G, 1920's

Used in telegraphy systems to amplify power and and enable equipment to be powered locally. Post Office Relay 'G' on a pluggable base.

The 'G' Relay is a later model of the Gulstad Relay see item A0238. It works best in Duplex Systems. "Duplex working consists in the simultaneous transmission of two messages in opposite directions over a single wire connecting two stations "(sic) P249 Telegraphy T.E. Herbert 1906 see item A0252 for types of telegraphy relays.
Suitable for use on a single needle telegraph or double plate sounder. It has double throw contacts and is polarised, (has a magnet).

A0253

POST OFFICE RELAY TYPE B No 9534, 1920's

Relay used in telegraphy acting as a form of amplifier for the signal, sensitive coils moved the contacts which controlled equipment that could be powered locally. Post Office Standard Relay 'B'
This relay replaced earlier forms known as 'A' having coils of 100 ohms instead of 200 and being shorter in length. Relay 'B' also sometimes having differential coils (two winding on each coil) It can be of the polarised (see item A0239) or non polarised type the polarised version has a magnet and can be neutralised, as in use with the double plate sounder item A0227, provided it has double throw contacts, which means the pole or tongue 'T' held between M(mark) and S(space) contacts. The relay shown only has a single throw contact, and is not polarised (no Magnet).

Types of telegraphy relays

'A' Relay earlier version of relay 'B'.
'B' Relay can be polarised or none polarised. With differential coils. And single or double throw contacts.
'C' Relay larger magnet and similar to 'B' Relay
'D' Relay not polarised and does not have differential coils. (Much cheaper).
'G' Relay later version of Gulstad Relay

A0252

POST OFFICE RELAY TYPE B No 7938, 1920's

Used in Telegraphy to amplify the power lost on long cables, by activating a sensitive coil which moves contacts that operate equipment powered locally. Post Office Standard Relay 'B' taller version.

This relay replaced earlier forms known as 'A' having coils of 100 ohms instead of 200 and being shorter in length. Relay 'B' also having differential coils (two winding on each coil) It can be of the polarised (see item A0239) or non polarised type the polarised version (taller) has a magnet and can be neutralised as in use with the double plate sounder item A0227, provided it has double throw contacts, which means the pole or tongue 'T' held between M(mark) and S(space) contacts. The relay shown has a single throw contact. and is polarised (Has a magnet).
See item A0252 for types of telegraphy relays.

A0254

SIEMENS GIANT TELEGRAPH RELAY, 1930's

Hermetically sealed (watertight) Large Telegraphy Relay in Brass container.

A0774

GPO REVERSING RELAY, 1950's

Relay used for reversing polarity of lines, made from an old Morse sounder.
Originally sold at the BT Museum Auction

A0081

BRITISH RAIL RELAY, 1957

Originally sold at the BT museum auction .
Last used in 1957

A0082