[Boatanchors] compairson of 5R4 tubes

[John King]

I note that there are various 5R4 tubes with different letters after the  5R4, which I suspect refers to the bulb shape, height or other style designations. I am going to order a number of 5R4 tubes for older transmitters such as DX 100s and early Viking transmitters. Is there any difference other than style between the various 5R4 tube versions? Some versions are significantly cheaper than other versions. What are your thoughts regarding the best bang for the buck for these old boatanchor transmitters? Thanks and 73, John, K5PGW