BRIMAR TUNOGRAPH TUNING INDICATOR, 1933

The Brimar 'Tunograph' is essentially a visual resonance indicator, and as such can be used in a radio receiver to facilitate and indicate correct tuning. This is the result of research to provide a means of inexpensively indicating the strength of tuned radio signals. In the 1930's the Superhetrodyne receiver was becoming more popular, this enabled automatic gain control to stop the overloading of tuned signals and provide maximum sensitivity for weak ones. The AGC circuit produced a flat output response from the Intermediate stages of the receiver making it difficult to tune to the strongest part of the signal. Tuning indicators were the answer to this problem,
The following was taken from Brimar Sales documentation.

'' In receivers employing automatic volume control, many people experience considerable difficulty in tuning accurately to the wanted station. When the Brimar 'Tunograph' is employed, however, this is simplicity in itself. The 'Tunograph' is a modification of the well-known Standard Telephone's Cathode Ray Oscillograph tube, (item A1304) operating on precisely the same principal, but produced at an extremely competitive price for incorporation in radio receivers.''

Once launched the Tunograph was overtaken in 1935 by the American RCA 6E5G which rendered it obsolete overnight.
It is a small cathode-ray tube, where the electron current from the cathode, was focused into a narrow beam and passed through a hole in the anode to a fluorescent screen. A pair of plates were used to deflect the spot and this deflection depended upon the signal strength.

Nortel Collection

A1303