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. Also made in Italy by Fivre. The 813 is a work horse .
These tubes were designed in 1937, and yet it is hard to find anything comparable on the market today! They are far more stable in GG operation than either 811 or 572 tubes, and usually can be run without parasitic suppressors. According to data presented in the last edition of Orr's Radio Handbook, they even have better IMD performance than a 572 or 3-500Z. Just remember to use a pi-net input for best performance. A pair will run at 600 watts output conservatively, but many hams have pushed them much harder. They seem to be indestructable, and because so many were made they are still reasonably available! Many hams have reported that they have been using the same pair of tubes for decades. The early graphite plate versions probably have a bit more reserve plate dissipation than the metal plate varieties. RCA, GE and others made these tubes. Cooling requirements are very modest, a small fan moving air over the tubes is all that is required.
Compliments of the energizer bunny .
