Understanding CCS vs CVS

[tvrgeek]

OK, made it through Morgan Jones. Almost understand it. Just need to do a lot of playing with load lines and comparison it to my various samples and I could be dangerous.

What he did not describe is some why's about CCS vs CVS vs regulated B+. Only real comment was CCS was fantastic for a diff amp stage. I don't quite understand why CCS is class A only, or the effective plus and minus of all three technologies. Is there another reference that discusses this more completely?

Secondly, I would bet some smart fine gentleman has put all this tube parameter selection stuff into a model somewhere. Any tips on where I might find such a thing? ( Now I have a clue what it means, I am not afraid to use a tool. I don't believe in calculators until you can do the math. Hint, I learned on a slip-stick).

[barretter]

Have you been to John Broskie's Guide to Tube Circuit Analysis & Design ?

[tvrgeek]

Nope, new one to me. ( I am new to tubes). Thanks.

[SY]

MJ explains it pretty thoroughly. Basically, an ideal CCS has infinite impedance and will assume whatever voltage it needs to in order to keep the current flow constant. It's also called a Norton source. A constant voltage source (or a Thevenin source) will pass whatever current is necessary in order to hold its voltage constant.

A B+ regulator is one example of a voltage source (not ideal, but close!).

[tvrgeek]

TubeCad. Cool. Printing several of his articles. ( I have a hard time reading PDF on a screen. Something about how they smooth)

[tvrgeek]

Originally Posted by SY

MJ explains it pretty thoroughly. Basically, an ideal CCS has infinite impedance and will assume whatever voltage it needs to in order to keep the current flow constant. It's also called a Norton source. A constant voltage source (or a Thevenin source) will pass whatever current is necessary in order to hold its voltage constant.

A B+ regulator is one example of a voltage source (not ideal, but close!).

Understand what a ccs and cvs are, but as far as their effect on how a tube stage functions is where I am reaching for.

Now, you are confirming that a regulated B+ is essentially the same functionally as a CVS in the cathode? Just that a B+ regulator has to run at several hundred volts, and placing it on the cathode means at a few volts. Do I have that? Hense something like a RLD is a slick cheap way to obtain more predictable behavior. But would not a 317 used in the normal voltage regulation mode be easier providing enough dropout margin than a hundred LED's? Noise or response time etc cone in to play?

I don't get why a ccs forces class A. Should it not still be where the bias point is set? I am catching on, but slowly. I have not been able to visualize all of the subtel things tubes do. Hey, a Snoopy smile!

[SY]

But would not a 317 used in the normal voltage regulation mode be easier providing enough dropout margin than a hundred LED's?

Sure it would. However, it's a lousy voltage source at high frequencies and has pretty pathetic overload recovery if it's bypassed properly. The idea of using the LEDs was that the recovery was instantaneous and they maintain their low dynamic impedance at high frequencies.

[SY]

I don't get why a ccs forces class A.

What's the definition of Class A? That should answer your question...

[tvrgeek]

LET, faster, makes sense.

Well, in a PP stage, that would mean the entire swing remains within the conduction range of both tubes. They would have to overlap completely. Which would beg the question why not make it simpler and build it SE with the two tubes in parallel and change the transformer. appropriately. I know I am missing something.

With the cathode voltage held exact... deleete, delete delete. Need to visualize some more. Otherwise I will have problems removing my foot from my mouth.

[Eli Duttman]

Originally Posted by tvrgeek

LET, faster, makes sense.

Well, in a PP stage, that would mean the entire swing remains within the conduction range of both tubes. They would have to overlap completely. Which would beg the question why not make it simpler and build it SE with the two tubes in parallel and change the transformer. appropriately. I know I am missing something.

With the cathode voltage held exact... deleete, delete delete. Need to visualize some more. Otherwise I will have problems removing my foot from my mouth.

PP "iron" costs LESS than SE stuff of equivalent capability. Cancellation in the O/P trafo makes B+ ripple less problematic. Keeping 1 tube from hogging the current, when a parallel setup is used, is a PITA.