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RE: RH84 test amp: multiple problems found ...

Posted by Tre' (P) on September 24, 2016 at 11:50:44

In Reply to: RE: RH84 test amp: multiple problems found ... posted by DAK on September 24, 2016 at 11:03:24:

I probably shouldn't say anything but elblanko just posted a link to a great article by Corwhurst where he explains that if the grid line spacing is not even along the load line, to the left and to the right from the idle point, harmonic distortion is the result.

Read the "Load line conclusions" starting at the bottom of page 2.

With the 12at7 I can not see where a operating point and load line can be placed where the plate voltage swing will be even to the left vs. to the right of the operating point. (P.S. 450vdc at 5ma. and 350vdc at 7.5ma. look OK but the tube is only rated to 300vdc plate so we can't use those operating points. We have to stay below 300vdc plate)

No matter where you operate the tube and no matter what the angle of the load line, the plate voltage will change much more when the tube is driven along the load line to the left of the idle point vs. to the right.

A linear tube has even spacing between the grid lines and it's easy to fine a operating point and a load impedance that causes the tube's plate voltage to move in a equal and symmetric way, to the right vs. to the left.

Tre'

Have Fun and Enjoy the Music
"Still Working the Problem"

• http://ken-gilbert.com/images/pdf/acpart1.pdf   (Open in New Window)

Edits: 09/24/16 09/24/16

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