The National Signal Meter SM-57 was an external accessory designed for the National NC-57 receivers. The SM-57 plugs into the rear of the NC-57 chassis by means of octal plug and socket. The SM-57's dial lamp gets its power from the receiver. Has a set-screw needle limit adjustment. The SM-57's cabinet matches the receiver.
This one was working when removed from an NC-57 Receiver.
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