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In Reply to: RE: Dave... posted by PakProtector on June 14, 2021 at 03:20:24
I initially simmed this with a cascoded 10m45 since I already had the circuit built and indeed the values needed to be matched which seemed to confirm TK's original criticism. Then I went to a single lowly 10m45 and found for a 6SN7 with a 30,000Ω resistor on the left tube I needed a 30,775Ω to match the outputs from 100Hz to 1kHz. This combined with broskies use of the term "slightly" got me into this discussion. If this is picking nits then so be it but there is probably an equal chance of the same conversation happening if his underlying assumption was the mythical ideal CCS. If you look at his audience, I suspect a good majority of them fall into the group who think a single 10M45 is close enough to the ideal which makes me not take issue with his statement and I still feel adding the assumption of the ideal and then calling it in error is more akin to a cheap shot than a valid criticism.
dave
Follow Ups:
I can read the 10Mxx spec sheets...LOL Don't mistake me for thinking that beast is a good CCS used singly. Your spice results about parallel what I discovered whilst running longer and longer resistor tails( at higher and higher voltages ). The chip's specs are basically honest.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
I don't think it a question of "cheap shots" or anything like that at all.
Personally, I have an extremely high opinion of John Broskie, and I love the clarity and the precision of his articles. They are also very pedagogical, which is great.
Anyone can make the occasional mistake, though, and it is not at all a "cheap shot" to draw attention to the very exceptional slip-up if it occurs.
As I said, I like the clear and pedagogical style of his articles. But in an article on the long-tailed pair, the key pedagogical distinction to be made between the case of a cathode resistor connected to a negative voltage source, versus the case of the CCS, is that in the former one needs unequal anode resistors whereas in the latter case the anode resistors should be equal. One could certainly go on, after having made this clear pedagogical point, to discuss what happens when the CCS is not giving a truly constant current. But it just doesn't seem to fit with his usual clear style of writing for him to be assuming when he first introduces the CCS that it isn't a true CCS.
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