Quote:
Originally Posted by Electronic M
One quick way to find which tube is better would be to check introduction dates...Often the newer interchangeable type was an improved version of the older one.
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This was actually a great idea Tom. I looked up the 6BQ7, 6BQ7A, and 6BZ7 intro dates. The 6BQ7 came first with a mu of 35 per section. Then came the 6BZ7 with a mu of 38 and lower noise. RCA promptly retooled the 6BQ7A to match the noise figure of the 6BZ7 and upped the mu of each section to 39. The 6BK7 and 6DJ8 can also sub in parallel heater circuits, both offering an improvement over the 6BZ7/6BQ7A in a cascode arrangement. Then along came the Nuvistor and the rest is history.