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).
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).
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!).
A B+ regulator is one example of a voltage source (not ideal, but close!).
TubeCad. Cool. Printing several of his articles. ( I have a hard time reading PDF on a screen. Something about how they smooth)
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!
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.
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.
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.
And, for us capacitor phobes, you can keep the PS caps out of the signal current loops.
Visualized it all night and stared at the schematics a bit. I think I understand cvs. Let me take a crack at the ccs. It still requires the bypass cap or else it would try and track the grid making the plate current constant as well. The ccs should be pretty slow, so it only effects the bias, not the AC operation. You loose the feedback caused by varying drop across the cathode resistor. I just can't get my head around why it remains in class A as long as it has a bypass cap.
A bit early in my education, but do parallel tubes current hog like a bi-polar or self balance ( sort of) like a FET?
Depends on what you're using it for. The capacitor bypass causes it to stop being a CCS at higher frequencies. If you're using it in the cathode of a diff amp, that's not what you want. Or if you're using it as a plate load, ditto, no bypass cap. The only time people use a bypass cap on a CCS is if they're trying to use it in the cathodes of an output stage, and there (because the current is constant), you're restricted to class A, bypass cap or no.
They don't self balance, but as long as they're not gassy and the grid leak resistor isn't larger than the datasheet-rated max, they don't tend to run away.
Nope. Thanks dsa, I also printed a pile from tube cad journal so I can go hold up and read some more. I am sure I am close.
Guess I was not clear. I am thinking about an output PP stage. No problem understanding a diff amp. or on the plate. Following the mods on the MENG amp. I just can't see: "you're restricted to class A, bypass cap or no" I don't see why it does not produce totally a ccs, as in no audio, no amp except as you said, with the cap it stops being a ccs. Somthing big I am missing. Will check back tomorrow after I have read today's gleanings and articles. 200 pages or so.
Guess I was not clear. I am thinking about an output PP stage. No problem understanding a diff amp. or on the plate. Following the mods on the MENG amp. I just can't see: "you're restricted to class A, bypass cap or no" I don't see why it does not produce totally a ccs, as in no audio, no amp except as you said, with the cap it stops being a ccs. Somthing big I am missing. Will check back tomorrow after I have read today's gleanings and articles. 200 pages or so.
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