RCA 12BH7 Black Plates versus Grey Plates

[ceylon]

What is interesting is they made tubes for each other and for OEMs. So a RCA tube could be their own, an Amperex/Phillips/Westinghouse, a Mullard or a Telefunken depending on if and who they outsourced manufacturing. So like a RCA EL34 that is marked 6CA7 made in England with red letters was a black plate tube made by Mullard. View attachment 128472

Tube manufacturers outsourced with each other either making the parts or the whole tube.or would collectively engineer a tube and one manufacturer make them all. The plates EI/Tesla in Yugoslavia made Telefunken 12a_7 tube plates. and the EL84 but also made the plates to assemble for Ton-sol back then. EI/Tesla had RCA make their EL34. But also back then Ton-Sol had Amperex make tubes so you will see Ton-Sol made in Holland was an Amperex build.

yes, manufacturers bought, re-labeled and re-sold each others tubes. in addition, many vendors and retailers rebranded the tubes they purchased prior to retail sales. i did not know maufactures bought parts from each other--there always seem to be noticeable differences upon attentive inspection

EI and tesla arent related. tesla was czechoslovakia. tungsram was UK then hungary.


what do you think of RCA 12BH7 Black Plates versus Grey Plates?

 

[ceylon]

i have never compared the RCA black vs grey plates. i have never owned the grey plates and may have enough 12BH7. enough experienced tube audio folks prefer RCA black over grey plate that i never bothered to buy the RCA grey.

in generqal the tube type seems a bit dark in a circuit not optimized for their use, in the only ony piece of gear i own has ttransformers that can easily handle the addition heater current of 12BH7. i wish i had more experience with this type as a driver or perhaps low wattage push pull amplifier. soon enough ill build a powere amp and an aikido line stage for 12BH7. i cant make up my mind to use 12BH7 or 5965 as cathode followers. even in a zero feedback circuit, i dont think the CF makes much a sonic difference. it certainly makes a difference in output impedance.