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In Reply to: RE: another interesting visual posted by Cleantimestream on December 24, 2012 at 13:01:40:
"A 5879 triode wired is rather interesting though."Not bad but compare that to a 6sn7 at about 14ma, 200 volts plate.
Notice how evenly spaced the grid lines are around the bias point?
When the grid is driven from -4 volts to -6 volts notice how much the plate voltage changes. Now look at the plate voltage change when we drive the grid voltage form -4 to -2. The plate voltage change is very close to being the same.
Also true for -4 to -8 vs. -4 to 0.
That's what we are looking for.
If the plate voltage change is not the same because the grid lines are spaced closer together to the right and farther apart to the left, (like they are with the 5879) the result is harmonic distortion.
Note, just use a horizontal load line. If the tube is not linear with a horizontal load (high impedance) it will only get worse as the load line is rotated toward the vertical (lower impedance load).
As the load line is rotated toward the vertical, following the load line, the grid lines get closer together to the right while getting farther apart to the left.
As an example I have arbitrarily picked a 12au7 (very non-linear tube) with a idle current of 10ma and 210 volts on the plate with a 10k ohms load.
The grid bias is -6 volts.
As the grid is driven from -6 to -12 the plate voltage moves from 210 to 260 volts. The plate has moved 50 volts.
As the grid is driven from -6 to 0 the plate voltage moves from 210 to 135 volts. The plate has moved 75 volts.
The grid has moved the same amount each way but the plate voltage has not.
The two halves of the wave form will be very lopsided. One half much larger than the other half.
This is where harmonic distortion comes from.
Even with a horizontal load line the plate moves 95 one way and 120 the other.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 12/24/12
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Follow Ups
- RE: another interesting visual - Tre' 19:15:21 12/24/12 (1)
- RE: another interesting visual - Cleantimestream 04:56:44 12/25/12 (0)
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