Re: Rogers B-510

[Eric Strasen]

Re: Spray-shield tubes. I’ve got a Rogers-Mjestic 7R621 for which I rounded up several Rogers and Marconi branded spray-shielded tubes with the help of some CVRS friends in Canada and a lot of patience. My most recent venture in the spray-shield world was with a 1933 Grigsby-Grunow Majestic (the first of many U.S. firms to use the "Majestic" brand name) Model 463 "Century Six." The G-G spray-shield tubes, which I suspect pre-date Rogers, are somewhat easier to find — but more often than not are non-functional. I wound up buying two or three of each type in order to find one that would work, and most of these tubes were N.O.S., N.I.B.! The G-G spray-shield tubes differ from Rogers in a couple aspects. All of G-G’s product, made in their own tube plant, are pre-octal. I don’t know of any U.S. manufacturer other than Majestic who made this type of vacuum tube, and Grigsby-Grunow was out of business before RCA introduced the octal tube. The spray coating on G-G’s tubes appears the same as Rogers, but does not cover the tube base like Rogers’ product. A ground connection from the G-G shield is made through one of the tube pins. G-G numbered their spray-shield tubes the same as non shielded tubes, but added a suffix "S". Thus, a 2A7 became a 2A7S, a 55 became a 55S, etc. Rogers created a whole different and sometimes confusing naming system for their spray-shield tubes.
So, if you don’t want to spend a lot of time and expense like I did on my two spray-shield radios, buy a non-shielded substitute tube, wrap a goat shield around it and ground the shield to the chassis. The substitute will probably function better than a spray-shield original anyway. There are substitutes for most (but not all) Rogers spray-shield tubes and you can find tube substitution lists on a couple of Canadian sites.