The Red Top from QRS Music is described as a super detector.
The following is from UV201.com:
The QRS Music Company produces and markets mechanical music items, and are best known for player pianos and rolls. The company is still very much alive and concentrating on their traditional market, but for a brief time in the 1920's, they also sold a line of radio tubes.
The QRS tubes were distinctive, to say the least. They were dipped in a clear red lacquer and, appropriately, called Red top tubes. Naturally, this had no effect on their operation, but they look great when they are lit. In the early days of radio, when this technology still had a magic quality about it, appearance was as important as actual performance. The exotic appearance of the QRS tubes, with two red lights burning in each one, must have been very impressive to the gullible customer.
Functionally the super-detector, is equivalent to the UX-200A. It is actually two triodes connected in parallel internally.
The dome has been dipped in red lacquer. and with a hole in the gettering the filament glow would be visible.
The base cap features a logo with an S in a rectangle inside a horizontal diamond.
The wide glass tube envelope is 35 mm in diameter, and excluding the UX4 base pins is 91 mm tall.
References: data-sheet & UV201.com.
Absolute Maximum Operating Conditions¶
PDF scanned from an original document held by the museum
Updated July 06, 2021.