[Amps] tube output power

[John Lyles]

When I worked for BE, I designed the cavity amplifier that was put into production in the FM3.5A and FM5A FM transmitters. The 'standard' tube used for 3 - 5 kW FMs that used tetrodes was the 4CX5000A, in RCA and other makes of power amplifiers. George Badger of Eimac showed us their new shortened 4CX3500A, which broke the traditional wisdom, and it ran beautifully in the 5 kW model (actually 5.5 kW with 110% power type accepted). While this isn't 2 x the dissipation rating, it does show that the tube chosen for a particular power level depends a lot on other things like cathode emission, expected lifetime, class of operation, screen dissipation, as well as plate dissipation. We did built a triode transmitter as well, using the 3CX1500A7/8877, although it was only running 1750 watts output. And the 8990/4CX20,000A was used in the FM30. In no case am I aware that we actually built PAs that produced output powers that were exceeding twice the plate dissipation. We were fairly
conservative, but we had a lot of customers and didn't want to fail in the marketplace at the time. 

John
K5PRO