Beam-power tetrodes I have known

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Two of my Friday Lunch companions play guitar -- one acoustic and one electric. Guitar pickups, amps, and other things luthier-ish come up in our free-ranging discussions over British ales and bangers and mashed or margaritas and molé.

I found this fun 2014 BBC documentary on Marshall Amps -- Play It Loud: The Story of Marshall Amplifiers -- yes, some go up to eleven, but no further spoilers here; watch it yourself. 

I noticed that Marshall were using KT-88 "valves," which are similar to the 6550 I used in the 25W bootleg AM transmitter I built in 10th grade.  KT-88s are also in the 75W McIntosh amp I rescued from the dumpster when SRI's Sound and Vibration lab was being shut down.  My mom's old tube amp used 6V6GTs and the PA amp my Uncle Norman used for Bingo Night at their shul used 6L6GTs.  All these are beam power tetrodes... so are the Eimac 4CX250B and 4CX5000A used in WRPI's old FM transmitters.

Poking around for info on the KT-88, turned up issue #19 of a magazine called Vacuum Tube Valley, which has a long article on the history and various versions of the KT-88 and the sonic merits of each. In fact, most of the issue is devoted to the KT-88.

Interesting, but the real find was the next article: part two of a fairly-scholarly series entitled "The Contest for High Fidelity: Western Electric vs RCA" by Scott Frankland. It talks about Edison, Fessenden, DeForest, Nernst, Steinmetz, Whitney, Langmuir, ... and the origins of industrial research in the US. George Wise, GE R&D's historian, who I got to know when I worked there in the 80's, is cited and quoted. Jackpot! 

I found Part 1 in issue #18, which ends with, "To be continued. (This is the first of a twelve-part series on the early history of high fidelity and the related electronics)."  Twelve parts!! Holy suppressor grid, Batman! (and, yes, I know that tetrodes don't have a suppressor grid) 

Back to archive.org to grab issue #20 and it says "Due to time constraints and space requirements, Scott Frankland's Contest for High Fidelity Part 3 is not in this issue. It will be featured in VTV issue #21, along with several other interesting articles."

Well.... sadly, issue #20 was the last issue of VTV, so all we have is the first two parts. Still well worth a read. 

Location: Menlo Park, CA, USA

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