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In Reply to: RE: Too low plate R value for a triode ? and CCS substitution? posted by Tre' on March 23, 2017 at 07:59:11
didn't you just argue with Victor that the load has no effect on the gain of a stage?
from the SET asylum..
Lowering the plate load resistor will limit the max output swing but will not lower the mu (and therefore the gain of the stage) at all.
now you state that going to a CCS will increase the gain which seems in direct opposition to your statement above.
I realize this is not a black or white argument and the truth lies in the middle and requires a judgement call as to what constitutes a change in relation to the other mitigating factors. From a purely technical standpoint a CCS gives you gain = µ and a dead short give a gain = 0 so by varying the load you can set your gain anywhere inbetween those two points :-)
dave
Follow Ups:
What I was trying to say, and doing a poor job, is this.....If you keep the plate load resistor high enough as to not substantially increase the HD, the amount of gain reduction from a proper value plate resistor to a less than optimum value plate resistor is so small as to be of no real consequence.
Of course the gain will drop if you load the tube with a vertical load line but why would anyone do that?
I guess I should ask Victor.
"I have just bought a BAT VK5se preamp for good deal.
What I have found is the plate resistor being abnormally low value for the parallel 2 section of 6h30. The plate R of 6h30 per section shown in EH datasheet is 840 ohm per section then parallel 2 section is 420 ohm.However the plate resistor is only 1250 ohm which is less than 3 times of 420 parallel section of 6h30. Is it normal for high priced preamp design?"
So Victor wasn't just "saying" that you can lower the gain of a tube by loading into a vertical load line, Victor is actually "doing" just that.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 03/23/17 03/24/17 03/24/17
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