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6AK5 in Triode - Plate Resistance?
6AK5 in Triode - Plate Resistance?
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Old 2nd October 2019, 01:36 AM   #1
FlaCharlie is offline FlaCharlie  United States
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Default 6AK5 in Triode - Plate Resistance?

I was able to find the curves for the 6AK5 wired in triode but no other info. Does anyone know the plate resistance?
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Old 2nd October 2019, 04:23 AM   #2
PRR is offline PRR  United States
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rp is just the slope of the line *around your selected bias point*.
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Old 2nd October 2019, 12:24 PM   #3
FlaCharlie is offline FlaCharlie  United States
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Quote:
Originally Posted by PRR View Post
rp is just the slope of the line *around your selected bias point*.
Thanks. So closer to vertical is lower and more toward horizontal is higher?

How did you come up with the figures 3.3k and 9k?
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Old 2nd October 2019, 02:06 PM   #4
DF96 is offline DF96  England
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By estimating the slope of the curve.
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Old 2nd October 2019, 02:21 PM   #5
kward is offline kward  United States
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Take the orange tangent line shown at grid = 0V for example. That tangent line crosses 24 mA and 12 mA on the Y axis. The plate voltage at 12 mA is 66 volts and the plate voltage at 24 mA is 108 volts.

Therefore the inverse slope of that tangent line is (108-66V)/(24-12mA) = 3.5k
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Old 2nd October 2019, 08:46 PM   #6
FlaCharlie is offline FlaCharlie  United States
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Thanks guys!
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Old 3rd October 2019, 02:42 AM   #7
PRR is offline PRR  United States
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Quote:
Originally Posted by FlaCharlie View Post
How did you come up with the figures 3.3k and 9k?
_I_ grabbed the orange line and slid one end down to 0V 0mA. Then peeped the V and mA at the other end of the line. Math as the others say; simple division.

This also highlights the fact that rp is NOT a "constant". It is different around every operating point, and for large swings around that point.
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Old 3rd October 2019, 11:00 AM   #8
RajkoM is offline RajkoM  Bosnia and Herzegovina
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The PRR is correct, of course.
rp is variable and depends of the operating point.
Some posters here on tube forum, find that rp is determined by the curve Vg=0 only, and "everything else is the internal resistance of the tube".

I didn't even have the will to discuss with them about it.
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Old 3rd October 2019, 11:20 AM   #9
TonyTecson is offline TonyTecson  Philippines
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6AK5 in Triode - Plate Resistance?
you can even get the mu and the gm from that curve....
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Old 7th October 2019, 06:12 PM   #10
FlaCharlie is offline FlaCharlie  United States
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Quote:
Originally Posted by kward View Post
Take the orange tangent line shown at grid = 0V for example. That tangent line crosses 24 mA and 12 mA on the Y axis. The plate voltage at 12 mA is 66 volts and the plate voltage at 24 mA is 108 volts.

Therefore the inverse slope of that tangent line is (108-66V)/(24-12mA) = 3.5k
OK, here's what I'm trying to figure out . . . a poster on another forum measured voltages in his FX-01 preamp that uses these tubes in triode.

The PS has rails that measure +34v / -34v. He measured 51v plate voltage (plate to cathode). He measured -32.19v cathode to ground with tubes installed and -34.44v cathode to ground with tubes removed. So I figure the cathode is at +2.25v so the grid is at -2.25v.

Looking at the curves, that operating point doesn't even seem to be on the chart. Or maybe it's super close to the X axis?

Working off the -2v curve I get: (60v - 45v) / (0.8ma - 0ma) = 18.75k

Am I doing it correctly? I'm confused because the cathode resistor is 200 ohms and that would indicate (2.25v / 200) a current of 11.25mA.
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