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Old 1st October 2007, 11:11 PM   #1
m6tt is offline m6tt  United States
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Default 6lw6 tv sweep tube bias?

I picked up some GE 6LW6 tv sweep tubes today after digging around a room full of random tubes. They look interesting, but I cannot find much more data on them than is in TDSL/Tubedata/Frank's/Etc. I really need to know if I can drive them at all, I have 450 or so B+ on hand and -48 volts as well. Would PP Triode make sense here (I am working on modifying a destroyed PA system, I only want 40 watts or so for harp/guitar). I can't find load impedance either!
I saw a few posts here on these tubes, but nothing concrete...does anyone have either the data for these tubes or an idea of voltage and bias?
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Old 1st October 2007, 11:41 PM   #2
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The screen voltage limit on these is quite low - 250V... so triode mode would not make much use of them. Put 'em on eBay and buy a half dozen EL34s with the proceeds...
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Old 1st October 2007, 11:55 PM   #3
SY is offline SY  United States
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Or swap them with me! I like to use tubes like that in screen drive. Tom's right, they're not suitable for 'ordinary' audio output circuits.
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Old 1st October 2007, 11:58 PM   #4
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why not just use a 250V regulated screen supply, a 450-500V plate supply, and drive as you would a KT88?
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Old 2nd October 2007, 12:03 AM   #5
SY is offline SY  United States
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VERY nonlinear that way.
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Old 2nd October 2007, 01:28 AM   #6
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ah, that's unfortunate. guitar amp?
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Old 2nd October 2007, 01:45 AM   #7
SY is offline SY  United States
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Good thought!
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Old 2nd October 2007, 01:53 AM   #8
m6tt is offline m6tt  United States
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We had a 50-watt 6ca7 output PA. Something which the guitarist couldn't describe all too well happened which included "A flash at the TOP of the tube" "A very bad sound" "Bad smell" "turning the amp off immediately." The fuse was blown when I checked it. None of the resistors seem fried according to my DMM. I have been trying to get any kind of output tubes up here, and the local music shops want $60 for groove tubes and even my local electronics supplier wanted no less than $50 A PIECE for some 7591 russians. Blah. Off to the place with all the old TV tubes and miscellaneous. I found a Raytheon 5U4GB, which was a good deal, but I also found these wicked looking GE 6lw6 output tubes. I also found a single GE 6550A, sad there wasn't another one . Further research has indicated to me that A) they can handle 500+ volts on the screen for extended periods. B) Plate dissipation on these suckers is ridiculous. C) No one knows how the hell to bias them-no curves D) The anode cap will stick out of the amp _a little_, so I'd rather not have 500v sitting where idiots can touch or spill beer on it. Can anyone explain (grid voltage aside) how I figure out load impedance for these things if I cathode bias & triode them? I really don't want much wattage out of the push pull, 30-60 is really about all that's needed with a 2x12 in a small setting.
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If you have some of the more standard octal output valves you wanted to trade, I'd consider it...I'm not too far away from napa, might be travelling by soon. Some el34s or kt-anythings or even 6l6gcs would be fine, I have no real preference, except the wattage mentioned.
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Old 2nd October 2007, 02:20 AM   #9
jlsem is offline jlsem  United States
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Quote:
Or swap them with me! I like to use tubes like that in screen drive. Tom's right, they're not suitable for 'ordinary' audio output circuits.
I have a good-size box of new miscellaneous sweep tubes of that ilk that are looking for a new home. Free to anyone who will pay for shipping.

John
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Old 2nd October 2007, 02:38 AM   #10
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PM sent. Great quote btw. "we're in a tight spot!"
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