There is a 6LU8 pentode and triode model here.
For triode connected pentode, I suppose you can just connect Vg2 to anode in pentode mode to get triode model. It will be accurate if screen current has been modeled correctly (I don't see G2 param so don't think it's modeled) also and Vg2 is 120V(?), you can try see it's any good.
For triode connected pentode, I suppose you can just connect Vg2 to anode in pentode mode to get triode model. It will be accurate if screen current has been modeled correctly (I don't see G2 param so don't think it's modeled) also and Vg2 is 120V(?), you can try see it's any good.
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Here are some triode mode curves (of the pentode) for a Montgomery Ward USA 6LU8 tube (looks like Sylvania construction, but measures closest to a GE 6LU8 I have)
Vertical 20 mA/div, Horiz. 50V/div, Grid1 4V steps down from 0V
I measured a Sylvania tube and was similar except 7% less Mu.
I measured a GE tube and was nearly identical.
I measured an RCA tube and that had higher Rp (the grid 1=0V line at 200 mA was at 150V plate instead of near 100V plate for the others.) Noticeable roll-over in the curves too. If the other 6LU8 RCA tubes I have measure like that, I'm throwing them all out. (Koonw's curves above look like they are from an RCA one, obvious roll-over)
Vertical 20 mA/div, Horiz. 50V/div, Grid1 4V steps down from 0V
I measured a Sylvania tube and was similar except 7% less Mu.
I measured a GE tube and was nearly identical.
I measured an RCA tube and that had higher Rp (the grid 1=0V line at 200 mA was at 150V plate instead of near 100V plate for the others.) Noticeable roll-over in the curves too. If the other 6LU8 RCA tubes I have measure like that, I'm throwing them all out. (Koonw's curves above look like they are from an RCA one, obvious roll-over)
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Out of curiosity, I ran a curve trace on the 38HE7 in triode mode to compare with the 6LU8.
Like the 6LU8, the 38HE7 pentode should be good for 14 or 15 Watts Pdiss when run -without- the damper diode in the same bottle. This can be done by powering just the pentode with 21V heater across pins 10 and 12. (available on about 80% of the 38HE7s I've seen)
The 38HE7 Mu is around 4.2 versus 6.5 Mu for the 6LU8. However, the 38HE7 is only rated for 150V on grid2, while the 6LU8 is rated for 300V on grid2. But then 38HE7 has an 800 mA peak rating versus 260 mA peak for the 6LU8. So it just needs to run at lower B+ but higher current.
Vertical is 20 mA/div., Horiz is 50V/div and Grid1 is 7V steps down from 0V.
Same graph scaling as used for the 6LU8 above, except for the bigger grid1 steps here.
Also, the 38HE7 pentode appears to be equivalent to half of an old style (double pentode sub sections) 42KN6. Only $1 for 38HE7, still on the $1 list at ESRC. (note: 12HE7 is on the list too, but it can NOT be run with just the pentode only, so 10 Watt Pdiss)
Like the 6LU8, the 38HE7 pentode should be good for 14 or 15 Watts Pdiss when run -without- the damper diode in the same bottle. This can be done by powering just the pentode with 21V heater across pins 10 and 12. (available on about 80% of the 38HE7s I've seen)
The 38HE7 Mu is around 4.2 versus 6.5 Mu for the 6LU8. However, the 38HE7 is only rated for 150V on grid2, while the 6LU8 is rated for 300V on grid2. But then 38HE7 has an 800 mA peak rating versus 260 mA peak for the 6LU8. So it just needs to run at lower B+ but higher current.
Vertical is 20 mA/div., Horiz is 50V/div and Grid1 is 7V steps down from 0V.
Same graph scaling as used for the 6LU8 above, except for the bigger grid1 steps here.
Also, the 38HE7 pentode appears to be equivalent to half of an old style (double pentode sub sections) 42KN6. Only $1 for 38HE7, still on the $1 list at ESRC. (note: 12HE7 is on the list too, but it can NOT be run with just the pentode only, so 10 Watt Pdiss)
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