The Lincolnshire Heritage Exchange

PMBX 2/2b

The PMBX 2 switchboard is a manually operated switch, requiring an operator to connect all calls, each exchange line could be switched through to an extension for night service.

We have this 2+6 switchboard wired and working in our display, as well as having a 3+12 also on display.

These Switchboards were usually appropriate for small businesses and the operator would also act as a secretary or receptionist.

On the left we have the equipment associated with the switchboard.

The top unit is the power unit, this provides 50v dc to the switchboard and extensions and it also provides the ac ringing current.

In the middle can we have the cable connections, the plug to the right of that is where the switchboard connects.

The bottom unit is a relay set is for auxiliary apparatus like an external extension.  [click on the can to see inside]

On the right is the switchboard it’s self which has two exchange lines, six extensions and three connecting circuits.

How does it work?

On the first row we have the exchange lines on the first two switches, the next six are are the extensions and the last one connects the operators telephone.  The second row is identical to the first row.  The third row has only three switches, the first two being the hold for the associated exchange line and the third connects the audible alarm or sets the switchboard to night service.

Connection of the lines to the extensions or operator is achieved by moving the appropriate switches up or down in the first row and up only in the second row, moving the extension keys down in the second row applies ringing current.  So any key that is switched to the same position in a row connects them together, however the exchange lines are wired so that the second line will cut the first line off if moved into the same position.

Click on the switchboard for more detailed information....