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RE: How did the 6550 evolve?

Freo-1, hi. The 6550 was the brainchild of Tung Sol as was the 5881. RCA used the Tung Sol 6550 in many amplifiers including MI-9289 which yielded 200 W continous with four 6550 - cherry picked from the Tung Sol line. The 6550 was a tough tube. The MO Valve KT-88 derived from the 6550 not the other way around. It is not so easy to duplicate the quality and reliability found in tubes such as the TS 6550 built as they were at the peak of manufacture. The 6L6 is a sheet beam tube where G3 is the beam forming plate. G1 and G2 are wound to "shadow" each other in relation to the anode or plate. In this way are 6L6's related to the 6550. Count how many Beam Power tubes there are in a tube handbook. Lots. They all relate back to 6L6 - just one of many to use this principal. RCA tried using the RCA 6146 as an audio tube push-pull AB1. After all, it was RCA's tube. RCA billed itself as "The Fountainhead of Modern Tube Development" at this time though they did not develop the 6550. But, they had the 6146. Why not use it for audio - and Class C RF telephony, and Class B, and... One Tube. Does all. In practice it proved to be bias unstable. These amps were reworked for 6550. If you see a classic coke bottle 6550 labeled RCA it was made by Tung Sol. The RCA branded ones might just beat out the regular Tung Sol versions in transconductance. RCA only picked the cream. As you say the 6550A version is all GE.


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