> much lower plate knee voltages
At similar current-- not hugely different. At 15mA and 150Vg2: 6AU6 ~~40V, 7056 ~~60V. Enough to notice on test. Not enough to turn happy to sad.
At Vg2=150V, the 6AU6 does ~~15mA, the 7056 does ~~28mA. Both are far larger than most audio volt-amps need. We would tend to reduce Vg2 to more like what we need. This increases voltage gain, which can be used in other ways to improve overall linearity. For the same target current, 7056's Vg2 can be lower than 6AU6's, which will lower the knee voltage. I suspect they end up near the same place.
> depends on the operating conditions
Too confusing.
At similar current-- not hugely different. At 15mA and 150Vg2: 6AU6 ~~40V, 7056 ~~60V. Enough to notice on test. Not enough to turn happy to sad.
At Vg2=150V, the 6AU6 does ~~15mA, the 7056 does ~~28mA. Both are far larger than most audio volt-amps need. We would tend to reduce Vg2 to more like what we need. This increases voltage gain, which can be used in other ways to improve overall linearity. For the same target current, 7056's Vg2 can be lower than 6AU6's, which will lower the knee voltage. I suspect they end up near the same place.
> depends on the operating conditions
Too confusing.
8077 looks to be a 13.5V heater version of the 12BY7.
Citation II used 12BY7. Should be good.
If you want lots of gm, there is the 12HL7, same pinout as 12BY7 and 8077. High quality linearity (see triode curves below, no roll-over), might be micro-phonic. (frame grid)
If you want something that fits into a 6CB6 socket, then 6EW6 is your tube. (2 in series for 12.6 V Htr.)
Citation II used 12BY7. Should be good.
If you want lots of gm, there is the 12HL7, same pinout as 12BY7 and 8077. High quality linearity (see triode curves below, no roll-over), might be micro-phonic. (frame grid)
If you want something that fits into a 6CB6 socket, then 6EW6 is your tube. (2 in series for 12.6 V Htr.)
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Good afternoon Smoking-Amp
The plan as it stands is to find a 9 pin, 12V tube that I can use in place of a 6CB6. I'm building the RCA 50w amplifier.
The plan as it stands is to find a 9 pin, 12V tube that I can use in place of a 6CB6. I'm building the RCA 50w amplifier.
re: Wavebourn
That's good to know! Such a useful tube. Like a space age 12BY7.
I've been thinking about using a row of them for output tubes. Should be even less likely to be micro-phonic there. I'll bet 2 + 10 of them ring like a city of carillons though if I hit the chassis with a hammer. The Amplifier from H_ll that sounds like Heaven.
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That RCA 50 Watt amplifier uses -TWO- 6CB6s, so why not connect the heaters in series for 12 Volt?
Can get 6JC6 for $1. 6EW6 for $5
But, otherwise (9 pin 12.6V pentodes): 12BV7, 12BY7, 12DQ7, 12HL5, 12HL7, 12GN7, 12HG7, 12DT5, 12DB5, 12CS5, 12AU8 and more with triode+pentode
That's good to know! Such a useful tube. Like a space age 12BY7.
I've been thinking about using a row of them for output tubes. Should be even less likely to be micro-phonic there. I'll bet 2 + 10 of them ring like a city of carillons though if I hit the chassis with a hammer. The Amplifier from H_ll that sounds like Heaven.
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That RCA 50 Watt amplifier uses -TWO- 6CB6s, so why not connect the heaters in series for 12 Volt?
Can get 6JC6 for $1. 6EW6 for $5
But, otherwise (9 pin 12.6V pentodes): 12BV7, 12BY7, 12DQ7, 12HL5, 12HL7, 12GN7, 12HG7, 12DT5, 12DB5, 12CS5, 12AU8 and more with triode+pentode
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That 12HL7 triode curve set was taken a while back, but should be 50V/div horiz., 10 mA/div vertical, and -1.1V steps down from 0V on grid 1.
(Mu internal about 26-27, rp about 1250 Ohm at 30 mA) I just re-checked it with another 12HL7 tube on the tracer and that fits.
Screen supply rated for up to 330 V in pentode mode.
One thing different (besides gm) from the 12BY7 however is the 12HL7 pentode curves have some curvature in them from screen grid current. That's because the grids are not aligned, with g1 being a frame grid and grid 2 being conventional. So there is an optimum load Z for linearity.
On the other hand, 12BY7 has aligned conventional grids and very straight pentode curves, which allows continued linearity at higher load Zs.
(Mu internal about 26-27, rp about 1250 Ohm at 30 mA) I just re-checked it with another 12HL7 tube on the tracer and that fits.
Screen supply rated for up to 330 V in pentode mode.
One thing different (besides gm) from the 12BY7 however is the 12HL7 pentode curves have some curvature in them from screen grid current. That's because the grids are not aligned, with g1 being a frame grid and grid 2 being conventional. So there is an optimum load Z for linearity.
On the other hand, 12BY7 has aligned conventional grids and very straight pentode curves, which allows continued linearity at higher load Zs.
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In my amp it sees 480V while cold; when hot gets down to 250V through a 27K resistor. In pentode mode, of course!
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