L. M. ERICSSON
SWITCHBOARDS No. 651 - 654

No. 651 is shown pictured to the right.

As supplied to the National Telephone Company, Ltd.

These boards are entirely enclosed, the wood-work being of very superior finish and beautifully polished.
Fitted with a jack and indicator for each line, and with pairs of plugs and cords, combination ringing and speaking keys, and ring-off indicators for making the connections.

When operating, pulling the key forward puts the service hand micro-telephone into circuit, and pushing it backward puts generator current on to the calling cord. The central position of the combined key is the through position. A so called "ringing-back key" is fitted at the right-hand end of the key shelf, and serves for ringing on the answering cord if the calling subscriber should leave his telephone while the connection is being made. The equipment includes a hand micro-telephone, hand generator, and a ringing vibrator, which indicates to the operator whether the ringing circuit is in order.

These boards are so constructed that four or five of them can be fitted side by side, sufficient space being left in the jack panels for fitting multiple jacks. The ring-off indicators, which are bridged across the cords, are of the tubular iron-clad type, and have a very high coefficient of self-induction.

Last revised: March 29, 2024