Rectifier-Element No. 205
The Rectifier-Element No. 205 was introduced circa 1906.  It is thought that they were first fitted to the Headset No. 1, which was introduced at that time, to stop loud clicks and bangs in the earpiece.  They are Selenium rectifiers.

As the Headset was fitted close to the ear, a loud noise could easily cause acoustic shock to the user.  Not a nice condition.

The Telephone No. 746 was the first telephone to have this device fitted in production and the Telephone No. 706 was fitted with these when returned to the GPO factories.

The device to the left is the 205B and to the right a 205.

Variants
205 - This have two 35mm fly leads.
205A - This has two tags is soldered to the circuit board.
205B - This has two spade connectors for screw terminals.  The spades are centred at 12mm. 
205C - This has two spade connectors for screw terminals.  The spades are centred at 9mm.
205D - This has two fly leads soldered to two spade connectors.

A Rectifier Element is effectively two diodes connected across each other but reversed to each other.  These are then encapsulated and fitted with fly leads or fixed terminals.

The picture below shows how to make a Rectifier-Element No. 205.  Two 1N4001 diodes are used.  There is a white line on each diode to make identification of each end easy.

It has been found that on 200 type telephones the 1N4001 diodes can sometimes cause faintness and 1N4118 diodes seem to work better.

 
 
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Last revised: April 01, 2021

FM