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Those Magnificent Television Tubes
Those Magnificent Television Tubes
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Old 27th August 2018, 07:47 PM   #1071
piano3 is offline piano3  United Kingdom
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What's the catch? Are the sockets hard to get?
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Old 27th August 2018, 10:17 PM   #1072
TonyTecson is offline TonyTecson  Philippines
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Those Magnificent Television Tubes
those are 9 pin miniature types, sockets are ubiquitous....
but i like the bakelite sockets better than ceramic types when buying chinese......

smoking-amp, great posts as usual, i hope we can have a "like button" in the future....
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Old 27th August 2018, 10:18 PM   #1073
TonyTecson is offline TonyTecson  Philippines
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Those Magnificent Television Tubes
Quote:
Originally Posted by smoking-amp View Post
Here are some triode mode curves for the 9DX base pentodes: 6LQ8 and 6HZ8.

6LQ8: 50V/div Horiz., 10 mA/div Vert., 0.5V steps (frame grid, about 50 Mu)

6HZ8: 50V/div Horiz., 10 mA/div Vert., 1 V steps (non frame grid, about 25 Mu)

You will have a tough time finding "real" triodes this good!

this might put the tube off the dollar list, but nice to know anyway...
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Old 27th August 2018, 10:40 PM   #1074
piano3 is offline piano3  United Kingdom
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I see, so the 9DX refers to the pin configuration then, is that right?

Indeed, SA's posts fascinating as always.
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Old 27th August 2018, 10:42 PM   #1075
TonyTecson is offline TonyTecson  Philippines
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Those Magnificent Television Tubes
yes and there are a lot of tubes that belong to that base, 9DX

NJ7P SQL Tube Database Query
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Old 27th August 2018, 11:54 PM   #1076
smoking-amp is offline smoking-amp  United States
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Here is the list (from the back of the GE manual) of the actual 9DX 9 pin mini base tubes:

6AU8, 6AW8, 6BA8, 6BH8, 6CX8, 6EB8, 6GN8, 6HF8, 6HZ8, 6JE8, 6JL8, 6JT8, 6JV8, 6KR8, 6KS8, 6KV8, 6LB8, 6LF8, 6LQ8, 6LY8, 6MV8, 10JA8, 10LW8, 10LZ8, and higher heater V versions of these

then (similar/compatible base) 6KT8, 6GN8, 6ET7, 6KU8

Keep in mind that getting a good triode curve does not guarantee reliable operation in triode mode over extended time. Some sweep tubes tend toward bias run-away in triode mode after long hours. But if you keep the B+ reasonable, they probably will work OK in triode mode. Usually 300V or 330V datasheet screen grid ratings for these. (versus some TV sweeps with just 250V ratings) These tubes were intended for low screen V (150V typical) in practical operation, so no need to push the B+ up too high anyway.

Good triode curves also mean low distortion pentode curves, due to the grid not being too close to the cathode. These can work great for the pentode driver scheme with N Fdbk to the screen grid.

Some of the other 9DX tubes need to be curve traced yet to see how good they are. I've just cherry picked the most likely ones so far. 6HZ8 was a real surprise, big enough to replace a 6BM8 for low power, low cost, two tube P-P amplifiers.

Last edited by smoking-amp; 28th August 2018 at 12:05 AM.
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Old 28th August 2018, 12:01 AM   #1077
TonyTecson is offline TonyTecson  Philippines
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Those Magnificent Television Tubes
i understand Don, will running those tubes at a lower B+ help?
i have run high transconductance tubes that way....
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Old 28th August 2018, 12:35 AM   #1078
smoking-amp is offline smoking-amp  United States
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I would guess that 400V peak in triode would work OK, but that's just a guess.
Maybe can go by some pentode tubes that do give triode ratings.

The screen grid support rod only has a small bit of mica between it and the grid1 rods. While typically a plate has a cut out air gap in the mica around the support rod. Any leakage over to grid 1 and away it goes...poof! Of course a low impedance drive that limits the (positive) excursion of grid1 would greatly help, so that probably should be a design emphasis. A SS diode limiter for grid1 (from cathode) would be a good idea. As well as a low Watt fusible cathode resistor. Or a CCS tail. A grid2 stopper resistor (to plate) would also be helpful for triode safety.

Last edited by smoking-amp; 28th August 2018 at 12:39 AM.
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