I'm sure that they will work fine if the screen grid is kept somewhere near 150 volts. I know that they don't live sitting idle at 300 volts. A pentode amp at 300 volts (or more) on the plates will live if the screen is kept at 150 volts or less. where the limit is on a triode connected tube, I don't know since I only tried 300 volts. These kind of failures take a long time to develop. One of my 6LW6's lasted for about a year before blowing up. I think it was the last one at 375 volts or so.
I haven't observed any gray plate 6W6's. I have a big bag full of used tubes from really old to not so old......all of them have black plates. So do all 6 of my NOS tubes.
I remember your post. I don't have any 12EN6, but I have 25 or so used 6W6GT's and a few new ones, so I plan to test them a bit further.
the 12EN6 and the 12W6 differed only in the tube marking, i believe
they are the same tubes...i bought around 40 tubes in all at the time when they were at U$1 at Rogalskie's...
i remembered that Anatoly liked the 6W6 a lot....
i guess i can attribute the success of that build to the fact that i
handpicked a quad that biased perfectly alike for all four that i used...
they are the same tubes...i bought around 40 tubes in all at the time when they were at U$1 at Rogalskie's...
i remembered that Anatoly liked the 6W6 a lot....
i guess i can attribute the success of that build to the fact that i
handpicked a quad that biased perfectly alike for all four that i used...
i run my tubes at 80%, but remember, tv tubes can take more heat from published specs.....
never seen a 6w6 with grey plate....all of mine are black plates...
my bad, guys, I (as a semi-young crowds) do not have boxes of tubes in my stash, neither I have decades of experience with "those magnificients". ..
Yet gray vs black was asked rather generally, for like e.g. 6AV5GT commonly exists in both. I have a sleeve of ea 6W6GT and 6AV5GT, planning to dedicate some time next year for experimenting on them and hopefully followed by a build.
80% ? that'd be hot. While working on SHIII (on which I will resume soon) I finally settled with very nicely working cathode bias network of Z+R+C, which allows to run a PP on 50% quiescent with same outcome as of R+C biased at 80%.
Pentode for Hi-Fi. .. kind of feels not exactly right to me, though of course the excellent results can be achieved. I tend more to the UL, but here same issue with G2 at about as much Voltage as plate arises. Along with regulated G2 the Pentode certainly requires higher Primary impedance, IME at least twice as for Triode; figured it as an approx rule of 3.5K (T) -> 5.5-6K (UL) -> 8K (P) p-p for small power tubes of 5-12 Wa plate dissipation.
BTW, for those who do not want the complicated PSU, instead of G2 regulation a simple 100-150V Zener does the job very well.
Yet gray vs black was asked rather generally, for like e.g. 6AV5GT commonly exists in both. I have a sleeve of ea 6W6GT and 6AV5GT, planning to dedicate some time next year for experimenting on them and hopefully followed by a build.
80% ? that'd be hot. While working on SHIII (on which I will resume soon) I finally settled with very nicely working cathode bias network of Z+R+C, which allows to run a PP on 50% quiescent with same outcome as of R+C biased at 80%.
Pentode for Hi-Fi. .. kind of feels not exactly right to me, though of course the excellent results can be achieved. I tend more to the UL, but here same issue with G2 at about as much Voltage as plate arises. Along with regulated G2 the Pentode certainly requires higher Primary impedance, IME at least twice as for Triode; figured it as an approx rule of 3.5K (T) -> 5.5-6K (UL) -> 8K (P) p-p for small power tubes of 5-12 Wa plate dissipation.
BTW, for those who do not want the complicated PSU, instead of G2 regulation a simple 100-150V Zener does the job very well.
50C-A10
With an internal Mu of 8 and 30 Watt Pdiss, it would seem to be in the 6L6GC - 6550 - KT88 class. From the pics below
from: Japanese Triode
it would seem that it is a beam pentode with mica insulators, that has been triode strapped internally. A Mu of 8 would space the screen grid out further from the grid1 than in a typical low Mu (3 to 4) TV Sweep tube. How far the grid posts are from each other on the Mica would likely be the key to long tube life in triode mode. I see 450 V B+ stated as the max, same as a 6L6GC screen grid rating.
Another factor could be whether the tube was back filled with something fully getter-able (like N2) before it was finally evacuated. Residual Argon (inert, non getter-able, 1% in air) is probably responsible for damaging the Mica insulators over time by ion bombardment in many tubes.
Might be interesting to compare the 50C-A10 triode curves with a triode connected 6550.
With an internal Mu of 8 and 30 Watt Pdiss, it would seem to be in the 6L6GC - 6550 - KT88 class. From the pics below
from: Japanese Triode
it would seem that it is a beam pentode with mica insulators, that has been triode strapped internally. A Mu of 8 would space the screen grid out further from the grid1 than in a typical low Mu (3 to 4) TV Sweep tube. How far the grid posts are from each other on the Mica would likely be the key to long tube life in triode mode. I see 450 V B+ stated as the max, same as a 6L6GC screen grid rating.
Another factor could be whether the tube was back filled with something fully getter-able (like N2) before it was finally evacuated. Residual Argon (inert, non getter-able, 1% in air) is probably responsible for damaging the Mica insulators over time by ion bombardment in many tubes.
Might be interesting to compare the 50C-A10 triode curves with a triode connected 6550.
Attachments
That 6C-A10 and the 8045G seem to muster a lot of current on the Vg1=0 triode line, about twice what 6550 or KT88 manage in triode mode. They must have a large cathode like the TV Sweep tubes. But most of the Sweep tubes have an internal Mu of only 3 or 4. One could use two KT88 in parallel for a sub, I suppose. Maybe just two 6L6GC (110 mA max DC each) in parallel would do for the 6C-A10 (200 mA max DC).
8045G rated 300 mA max DC, will take two 6550 or KT88 to match.
OR.... use a big sweep tube, and instead of jumpering g2 with the plate for triode, use a Mosfet follower driven by a 2 to 1 R divider from the plate to run g2. (doubling the Mu to 8)
8045G rated 300 mA max DC, will take two 6550 or KT88 to match.
OR.... use a big sweep tube, and instead of jumpering g2 with the plate for triode, use a Mosfet follower driven by a 2 to 1 R divider from the plate to run g2. (doubling the Mu to 8)
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OR.... use a big sweep tube, and instead of jumpering g2 with the plate for triode mode, use a Mosfet follower driven by a 2 to 1 R divider from the plate (to cathode) to run g2. (doubling the Mu to 8)
That might be the solution for "Triode" longevity too (from Sweep tubes). But that will double the "triode" rp.
That might be the solution for "Triode" longevity too (from Sweep tubes). But that will double the "triode" rp.
Several of my friends have Lux Amps SQ 38 using 50C-A 10 the Japanese made tubes are very expensive.
I modified a LUX 3045 amp using the 8045 with KT88's but you lose a lot of power the Lux 3045 has PCB's you would use in transistor radio!! the money men ruined this amp . Shuguang sells 50c -A10 not cheap and may not be very good. Has any one tried them?
I think the 8045 and 50C-10 is close to impossible to find, they bring lots of money on EPay.
I modified a LUX 3045 amp using the 8045 with KT88's but you lose a lot of power the Lux 3045 has PCB's you would use in transistor radio!! the money men ruined this amp . Shuguang sells 50c -A10 not cheap and may not be very good. Has any one tried them?
I think the 8045 and 50C-10 is close to impossible to find, they bring lots of money on EPay.
There are a few others that have identical guts as well. The 12L6, 25L6, and 50L6 have the same internals as the 6W6 except for the heater ratings. I have several tubes marked 25W6GT / 25L6. Note that the 6L6 and the 35L6 are each unique and have no resemblance to each other or the 6W6GT family.
The same guts also appear in a 9 pin miniature tube. The 6GC5 is a 6W6GT in a fat 9 pin bottle.
I like those X'mas tube ornaments. Now to design an amplifier that uses them without smoking them...
I saw the funniest illuminated Santa front lawn display this morning. An automated Santa steps out of what sure looks like a little "out house" on the front lawn, the door swings open, and he looks to either side. Like he's trying to sneak out without being seen. Maybe its from "Scrooge Products Inc". I laughed so hard.
The Mu of 8 versus 4 mod deal was to get some big sweep tubes to look like the 8045G tubes in triode mode. It reduces the voltages on grid 2 by 1/2, so the sweep tube should be happy in triode mode that way. (long life, avoids runaway)
Other than a gain change, the main effect on the sweep tube is that its rp would effectively double versus straight triode wired. (damping factor) But it should be approx. matching the 8045G then, so no problem for use in a LUX amplifier (the OT designed for that). Would be an issue in an OTL amp though, but nothing a little NFBK couldn't fix. Same output power.
I saw the funniest illuminated Santa front lawn display this morning. An automated Santa steps out of what sure looks like a little "out house" on the front lawn, the door swings open, and he looks to either side. Like he's trying to sneak out without being seen. Maybe its from "Scrooge Products Inc". I laughed so hard.
The Mu of 8 versus 4 mod deal was to get some big sweep tubes to look like the 8045G tubes in triode mode. It reduces the voltages on grid 2 by 1/2, so the sweep tube should be happy in triode mode that way. (long life, avoids runaway)
Other than a gain change, the main effect on the sweep tube is that its rp would effectively double versus straight triode wired. (damping factor) But it should be approx. matching the 8045G then, so no problem for use in a LUX amplifier (the OT designed for that). Would be an issue in an OTL amp though, but nothing a little NFBK couldn't fix. Same output power.
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