This Red Top from QRS Music is described as an amplifier and 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.
The two parallel triodes are not visible from the side. All their valves had the same construction and it is possible that they were selected for application on test.
The original box indicating that the intended use was as a detector and/or amplifier.
Thanks to Joe Gruber for sending the images.
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.