"6L6" _is_ a lot like peanut butter.
They change the formula every decade.
There was the 807, it was good, but expensive.
There was the Metal 6L6, 24.Mar.1936, supposedly a cheaper 807.
The 6L6 had many fathers and enemies. Someone else had a patent on Power Pentode, so the 6L6 had to work as good as a pentode yet appear to not be a pentode. A combination of spacing and side-bars do what G3 does in a pentode. A straight pentode is a pig for G2 current, RCA bought a patent that was deemed too expensive for production and invented a machine to make it practical, and got G2 current way down. Great tube, but a lot of hype around it.
The metal 6L6 was expensive, RCA also registered a glass 6L6G on 08.Jun.1936.
6L6 was so popular, Osram made something like it for the european market, the KT66. This does not seem to be a copy but a work-alike. If you don't strain it, you may hardly know a difference. In fact the original spec shows the same performace. But the original KT66 lacks the G2/G3 kinks of original 6L6 and may sound different when slammed. It could also make more power in amps designed for KT66.
The 6L6GA of 1943.
Coke-bottle went out of style, cylindrical was in, so 6L6GB.
Tung-Sol was tired of making good headlights, went into tubes, niche was extra-tough tubes for applications which were killing standard tubes. Their 5881 works in nearly any 6L6 socket but will take more abuse.
Tube major-improvement peaked in the mid-1930s, then developers rested or worked on getting costs down. Then a war with a few fabulous developments and a lot of old-warhorses.
Close examination of these tubes shows that the electrode structures varied from 1936 onward. Improvements, short-cuts, many different makers doing things a little different. Also the Power Pentode patents either expired, wer captured, or were cross-licensed, and pentode-like structures crept in.
But then came TV. Cost a LOT of money. If costs could be brought down total sales would rise. So the tube designers really changed things up. The 2nd biggest and costliest tube in a TV set is the H-Sweep tube. And that's kinda an Audio tube with some adaptations. Someone took the 6L6 cathode, re-thought all the rest, and made a great sweep tube. When that was in production they omitted the high-voltage cap and offered it as an audio tube. Because the 6L6 family was still SO popular, they called this nearly-new tube 6L6GC. But it's really a different tube than original 6L6.
Meanwhile the transistor was eating the tube's breakfast and going for the tube's lunch. Tube development mostly stopped. The people making them kept on for a couple decades, but also yard-saled their excess machinery to eastern europe where the Russians studied it (but they had their own good production, self-designed types and US/EUR work-alikes), then on to the Chinese.
6P3P is the Chinese 6L6 and may be made on some old USA machinery.
The Russians had several tubes like 6L6. 6p3s was in production a long time with many variations.
So which Jif are we picking? The original from 1958? The updated Jif of the 1990s when even dads picked Jif? How about Skippy, which fell into the claws of the Corn Products Refining Co. after stealing the name and stashing a cartoonist in a nut-hatch?
Use your ears.
Don't expect a tube to make music FOR you. It's just a tool, like a peanut crusher.
Topic: 6L6 VS. 5881 (Read 12824 times)