[Amps] multi-tube amplifiers

[Peter Chadwick]

Years ago, I designed a marine transmitter that had 3 6146B's in parallel. The available output power at a given IMD level ranged over about 3dB, because of variations in exciter IMD, power supply voltage variation and so on. This meant that in production, some of the transmitters could have reached rated power with 2 tubes, while others did need the three, and there wasn't anything quite big enough to do it with a single tube without overkill - the 8121 family were too expensive when compared with 6146Bs. I even know a guy who has a PA from an ex-marine tx which runs four 4-400s.
There were a number of transmitters in the '60's using fourteen (YES 14!) 4CX250Bs to get a kilowatt out, but they were distributed amplifiers with a very wide band instantaneous frequency range - and really poor mains to RF conversion efficiency.
Personally, I prefer one tube, but needs must when the devil drives, as the saying goes.....
73
Peter G3RZP/W6 (this week)