Well, I checked the grid exponents for 6L6GC, 6V6, 13E1 and EL34. The g2,g1 is aligned for the 6L6GC, 6V6 and 13E1 and non-aligned for the EL34.
6L6GC g2 exponent = 1.28, 6V6 g2 exp = 1.3, 13E1 exp = 1.36
and the EL34 g2 exponent = 1.5
Confirms my suspicion that aligned grids reduce the exponent for g2 from the 1.5 nominal (via aligned g1 grid wire shielding).
6L6GC g2 exponent = 1.28, 6V6 g2 exp = 1.3, 13E1 exp = 1.36
and the EL34 g2 exponent = 1.5
Confirms my suspicion that aligned grids reduce the exponent for g2 from the 1.5 nominal (via aligned g1 grid wire shielding).
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For reference, some sweep tube g1 exponents (2.0 is ideal for class A )
(and 2nd number is the g2 exponent):
21HB5A 2.3 1.4
6LQ6 2.05 1.05
6LG6 2.88 1.28
6GE5,6JN6,6GV5 2.5 1.4
6MC6 2.2 1.2
6DQ5 2.01 1.14
6LB6 2.26 1.33
6LR6 2.6 1.3
6LX6 2.8 1.2
6GT5 2.5 -- (g2 probably 1.4, no data avail.)
6LF6 2.1 1.37
6CB5 2.2 1.32
6LW6 2.8 1.4
6HJ5 2.33 1.3
6JC5 3.09 1.33
6L6GC 2.15 1.28
EL34 2.4 1.5
6V6 2.1 1.3
6GB5 2.25 1.47
10JA5 2.27 1.36
38HE7 2.63 1.23
13E1 2.06 1.36
300B 2.0 1.5
Well, that 13E1 is a lot better tube than 2x 6LW6's in parallel after all.
But the beam tetrode winner is the lowly 26DQ5 for only $3
However, the exponent for variation of Mu with current (versus Vg1 actually) in Triode mode is (g1 Exp)-(g2 Exp), and the 300B wins there.
Note:
Any tube with a g1 Exponent above 2.0 can have it reduced down to 2.0 using a low value tail resistor below the P-P class A stage cathodes (WE harmonic equalizer or Kiebert equalizer), so no need to get obsessed with 2.0 tubes for class A.
(and 2nd number is the g2 exponent):
21HB5A 2.3 1.4
6LQ6 2.05 1.05
6LG6 2.88 1.28
6GE5,6JN6,6GV5 2.5 1.4
6MC6 2.2 1.2
6DQ5 2.01 1.14
6LB6 2.26 1.33
6LR6 2.6 1.3
6LX6 2.8 1.2
6GT5 2.5 -- (g2 probably 1.4, no data avail.)
6LF6 2.1 1.37
6CB5 2.2 1.32
6LW6 2.8 1.4
6HJ5 2.33 1.3
6JC5 3.09 1.33
6L6GC 2.15 1.28
EL34 2.4 1.5
6V6 2.1 1.3
6GB5 2.25 1.47
10JA5 2.27 1.36
38HE7 2.63 1.23
13E1 2.06 1.36
300B 2.0 1.5
Well, that 13E1 is a lot better tube than 2x 6LW6's in parallel after all.
But the beam tetrode winner is the lowly 26DQ5 for only $3
However, the exponent for variation of Mu with current (versus Vg1 actually) in Triode mode is (g1 Exp)-(g2 Exp), and the 300B wins there.
Note:
Any tube with a g1 Exponent above 2.0 can have it reduced down to 2.0 using a low value tail resistor below the P-P class A stage cathodes (WE harmonic equalizer or Kiebert equalizer), so no need to get obsessed with 2.0 tubes for class A.
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Back in post #17 I stated that I was experimenting with dual drive as a way to avoid blowing the screen grid out of the tube when overdriven. Last night I proved that dual drive isn't foolproof either.
The weather has not been conducive to getting much done outside, or inside an unheated old mobile home (my storage location). It was -2 F this morning, and -10 is expected tomorrow night. So I piled up a stack of test equipment including a brand new digital scope that I bought before leaving Florida, and never used. I wired up a simple single channel dual drive test amp using a pair of small sweep tubes, the 6AV5GT. I expected 30 to 40 watts from them, which I got easily. I was squeezing the amp hard to find out just what it would do, when there was a white flash inside one tube, and poof....one of the grids was gone. Not sure which one yet....
The little amp was happily cranking out 80 watts at 2.5% THD. The supply voltage was 420 volts and the 300 mA current meter pegged when I passed 60 watts, so I don't know how much was flowing. It sat at 80 watts output with no signs of distress for several minutes, but blew up when I pushed it harder.
This is not a problem, and even expected with 50 cent hamfest tubes, but don't try this with expensive stuff.
The weather has not been conducive to getting much done outside, or inside an unheated old mobile home (my storage location). It was -2 F this morning, and -10 is expected tomorrow night. So I piled up a stack of test equipment including a brand new digital scope that I bought before leaving Florida, and never used. I wired up a simple single channel dual drive test amp using a pair of small sweep tubes, the 6AV5GT. I expected 30 to 40 watts from them, which I got easily. I was squeezing the amp hard to find out just what it would do, when there was a white flash inside one tube, and poof....one of the grids was gone. Not sure which one yet....
The little amp was happily cranking out 80 watts at 2.5% THD. The supply voltage was 420 volts and the 300 mA current meter pegged when I passed 60 watts, so I don't know how much was flowing. It sat at 80 watts output with no signs of distress for several minutes, but blew up when I pushed it harder.
This is not a problem, and even expected with 50 cent hamfest tubes, but don't try this with expensive stuff.
13E1
Hi this is just a short note to say that in my experience of 53 years building Tube (valve) amplifiers....the 13E1 strapped as a Triode with 375 volts on the Plate is without doubt the sweetest sounding Tube I have ever heard.....The mid range is to die for....very reminiscent of the Single Plate 2A3 except with bags of guts....good luck and go ahead and build it PP or SE you will not be disappointed. Not only there is very few Tubes that look so impressive on a chassis than the 13E1
Hi this is just a short note to say that in my experience of 53 years building Tube (valve) amplifiers....the 13E1 strapped as a Triode with 375 volts on the Plate is without doubt the sweetest sounding Tube I have ever heard.....The mid range is to die for....very reminiscent of the Single Plate 2A3 except with bags of guts....good luck and go ahead and build it PP or SE you will not be disappointed. Not only there is very few Tubes that look so impressive on a chassis than the 13E1
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