Purity and simplicity of amp design

[Hearinspace]

Yup , you're right. My bad. I was out to full course dinner. Got sucked in by an attitude and took the bait.
I know the circuit , I've actually built one (the topology) . . . and it works ! As soon as I posted I started wishing there was a delete function here. Thanks Sheldon.

[Hearinspace]

Sheldon, Sorry for the mess here. Still learning how to work with the forum's functions, I wanted to edit my post above but haven't figured out how to do it yet.

Anyway, I agree with you that I was wrong . Part of my clumsiness above comes from the fact that I didn't see the inductors as cathode bias elements. They aren't in series with the cathodes of the stages they get bias voltage for so don't carry their DC current.
The way it looks to me is, by referencing the local ground of the upper circuit to the B+ of the circuit below it, the drop across the choke acts as a grid bias , not a cathode one. But as you say, the inductor and diode are working together to get the full bias needed.

How's that?

[Sheldon]

Originally posted by Hearinspace
Sheldon, Sorry for the mess here. Still learning how to work with the forum's functions, I wanted to edit my post above but haven't figured out how to do it yet.

Anyway, I agree with you that I was wrong . Part of my clumsiness above comes from the fact that I didn't see the inductors as cathode bias elements. They aren't in series with the cathodes of the stages they get bias voltage for so don't carry their DC current.
The way it looks to me is, by referencing the local ground of the upper circuit to the B+ of the circuit below it, the drop across the choke acts as a grid bias , not a cathode one. But as you say, the inductor and diode are working together to get the full bias needed.

How's that?

No worries, and no apologies necessary. A little "edit" button appears at the bottom of a new post, for the poster. Just click on that and you can edit. It goes away after some time between minutes and maybe an hour, so you can't edit after that. But before that you can edit or delete the post.

Just to summarize the bias elements for clarity's sake:

The diode provides portion of the bias. It's dynamic resistance is lower than it's static resistance, so it acts like regular cathode bias, with a portion of the resistance bypassed. The current from the diode is returned to the supply common for the supply for that section.

At DC, the inductor acts like part of a fixed bias supply. The current from the section supply for the tube beneath the inductor goes through the inductor and creates a voltage drop across it. Since the grid is connected across the diode and the inductor, that voltage differential is added to the bias.

However, and I think this is the main point, the inductor is in the AC grid/cathode loop. It's influence will depend on the bypassing on one side, and variations in plate voltage at the other. I can't make a value judgement on it good or bad, just something to account for.

Sheldon

[Larry Lomax]

Originally posted by Hearinspace
I'll just toss on a couple more briquettes. Hope you don't mind some opinionated rants from an old fart on the other side of the boat.

First, if you haven't built anything then it might be a really good idea to build a well documented kit. I'm saying this in regard to getting a physical experience and feel for good practice in terms of design, layout, construction and safety. Many experienced builders liked studying the old military electronics manuals and one good reason why is that they never put a bunch of stuff in a lesson that wasn't essential to learning the lesson they were trying to teach, so you don't get overloaded with indigestible details . . . . CUT

Well, my intention was to write allmost the same... word by word...
Please, ponder on these hints... are good advice...