Eighty years ago this month, the August 1946 issue of Radio Craft carried this circuit for a one-tube intercom. One station was required on each end, but since the signal amplified both coming and going, it was capable of great range. It had been submitted to the magazine by one G. Boult of Ottawa, who reported that he had used it over two miles.

The circuit calls for a 70L7GT, but the editor noted that a 117L7 could be used, without the need for the line-cord resistor.