I bought a box of old raido parts. Carefully wrapped at the bottom were two Cunningham C-302 tubes. They have vacuum "tipped" tops, brass bases, and four short pins. The tubes have a golden hue. The writting on the bases indicate they are transmitting tubes. Can these tubes be tested? What year were they made? Any and all information will be appreciated. Wes

Hi Wes, Cunningham was a bootleg tube maker after WW1, he made tubes without patent license and the legitimate makers persued these backyard operators vigorously to shut them down. For reasons not well understood Cunningham managed to strike a deal with RCA to stop making his own tubes but to be able to sell RCA tubes with his name branded on them. At this time the first number identified the manufacturer, RCA used "2" e.g. 2o1, 200, etc. Cunningham tubes used the prefix "C3", so the RCA 201 was a Cunningham C301, etc. Your C302 was a low powered transmitting tube originally designated 202 by RCA and made from 1921. It was one of the very early production low power transmitting tubes made by RCA. I can't find any data readilly to hand but I'll see if I can find some in the next day or so. I'm not sure if it's a bright emmitter with a high temperature tungstan filament or a low temperature dull emitter. The golden color suggests it could be a dull emitter with a phosphorus or similar getter (to keep the high vacuum) rather than the more usual magnesium getter with its silver coating. Tungstan filament tubes usually didn't have a getter as they could tolerate a poorer vacuum without cathode poisoning. It would be good to know the condition of the tubes but I think they will be of most use as a collectible rather than to use them operationally. I'll see what I can find on them. Cheers, Don Black.

: I bought a box of old raido parts. Carefully wrapped at the bottom were two Cunningham C-302 tubes. They have vacuum "tipped" tops, brass bases, and four short pins. The tubes have a golden hue. The writting on the bases indicate they are transmitting tubes. Can these tubes be tested? What year were they made? Any and all information will be appreciated. Wes

Hi Wes, Cunningham was a bootleg tube maker after the first world war. He made tubes illegaly without patent rights and was persued by the legitimate makers for infringement. In a deal that's not well understood, Cunningham struck an agreement with RCA to stop making tubes but it allowed him to sell RCA tubes under his own brands. The tube numbers at that time indicated the maker by the first number. RCA tubes started with 2, e.g. 200, 201, etc. Cunninham tubes were prefixed by C3 (C300, C301). Your C302 is a Cunningham labeled RCA 202. They started production in 1921 and I think your tube would be made soon after. I don't have any data on it yet except it was an early low powered triode transmitting tube. The golden bloom inside the glass suggests it used a phosphorous or similar getter instead of the more usual magnesium gettering that silvers the glass. That suggests a dull emitter filament rather than the early tungstan bright emitter filament. I'll try and find some data. It would be good to know their condition but they're more likely to be of value as a collectible rather than an operating tube. Hopefully the care with which they were wrapped might indicate they were good when stored away. I'll get back if I can find more. Cheers, Don Black.

: I bought a box of old raido parts. Carefully wrapped at the bottom were two Cunningham C-302 tubes. They have vacuum "tipped" tops, brass bases, and four short pins. The tubes have a golden hue. The writting on the bases indicate they are transmitting tubes. Can these tubes be tested? What year were they made? Any and all information will be appreciated. Wes