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In Reply to: 1622 vs. 6L6 posted by zona jim on February 1, 2007 at 07:49:44:
ZJ,Sibley, in "Tube Lore" states that they are "6L6 selected for long life in theater sound systems, et al; derated to 15W." But, although the maximum Ep is still a guess, it's been well documented that you can often get away with higher plate voltages as long as you keep the plate dissipation low. Perhaps try it with 360V Ep while monitoring cathode current to keep the dissipation around 10W for a few hours - then creep up to 12 for a few hours, etc., and see what happens - the extent of your experimentation depends on how many of these valves you've got to spare/sacrifice. You might even get the full 6L6 dissipation as the power derating appears to be an attempt to extend the tube life - theatre sound systems in the late 1930s often had remote power amps in the ceilings near the speakers, etc., which made long life that much more desirable and having part of the sound cut out in the middle of a film was disasterous in those pre-TV days.
Follow Ups:
Hello Rob -Agreed! Since I am running adjustable fixed bias, I can do just what you are thinking - sneak up from 10W to a reasonable wattage. This is the only time I kind of wish I could see the plates. <: )
Thanks for your input, and it looks like I should get a copy of "Tube Lore". Sounds like a fun read.
Jim
ZJ,I heartily recommend the tome! While Duncan's TDSL and such have surpassed some of it's uses - TL was around before TDSL - there is a great wealth of advise within and it's a much quicker reference if you just want to determine "what a tube is" - the TDSL reigns if you seek parameters. Sibley's history of the industry in the USA is significant as is identifying manufacturing evolution. Hell, stick it in your bathroom and you'll never get your "bottle heads" off the throne
.
Finally; I have suggestion for my birthday. The web has plenty of sources for the tube details, methinks, but the background is what I miss. Shoot - it's too bad they don't have it as 'book by radio'.
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