Linear gain stage (glass)
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Nixie

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I was reading Wolcott's description of his tube-based linear gain stage (second stage described here, and couldn't completely figure it out. Can anyone comment on this? I went through the description several times, but couldn't come up with a clear circuit. For example, how does he make the plates see an effectively infinite impedance? The adding of feedback from other stages is also not clear.
 
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Quote:

Originally Posted by Nixie
I was reading Wolcott's description of his tube-based linear gain stage (second stage described here, and couldn't completely figure it out. Can anyone comment on this? I went through the description several times, but couldn't come up with a clear circuit. For example, how does he make the plates see an effectively infinite impedance? The adding of feedback from other stages is also not clear.


Try giving this a read:

http://www.dddac.de/op01.htm
 
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ppl

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Nixie

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ppl, why did you post all these links? I know what a White cathode follower and auto-biasing is. I was specifically asking about one part of the design.

Anyone know what the patents referred to are? The stupid USPTO site doesn't show any patents by Wolcott using the pre-1975 search.

EDIT: Strangely, the German patent database searches all US patents as well, including the pre-1975 ones which the USPTO website doesn't search...
I found four amplifier patents by Wolcott from the 60s. 3111630, 3328711, 3361981, and 3428912. I think the one I'm looking for is 3328711, figure 6 (use free.patentfetcher.com to get PDF). However, in the original link it said it has been significantly changed. Any comments?
 
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ppl

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Quote:

Originally Posted by Nixie
ppl, why did you post all these links? I know what a White cathode follower and auto-biasing is. I was specifically asking about one part of the design.

Anyone know what the patents referred to are? The stupid USPTO site doesn't show any patents by Wolcott using the pre-1975 search.

EDIT: Strangely, the German patent database searches all US patents as well, including the pre-1975 ones which the USPTO website doesn't search...
I found four amplifier patents by Wolcott from the 60s. 3111630, 3328711, 3361981, and 3428912. I think the one I'm looking for is 332871, figure 6 (use free.patentfetcher.com to get PDF). However, in the original link it said it has been significantly changed. Any comments?



all the info you need is in those links so since you still are asking this question
also the patent #332871 you reference is for a gas Burnner and only showes 4 figures see http://patimg2.uspto.gov/.piw?docid=...26RS=PN/332871

so how dose this relate to your question of obtaining a symmectricial output from A Elctron Tube moreover if you look at this link http://milbert.com/articles/CathodeP...Inversion.html your quest would end
 
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Nixie

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Quote:

Originally Posted by ppl
the patent #332871 you reference is for a gas Burnner


There was a missing 1 at the end; the correct number is in the first list of four written just above.

U.S. Utility Patent 3,328,711 -- Infinite Plate Load Impedance Amplifier
http://free.patentfetcher.com/Patent...tch&PN=3328711

Fig 6 is pretty different from the links you posted.
 
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erix

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Nice links ppl!

Thanks!

ok,
erix
 
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Ok now we add the correct patent number and you now state your wanting to know about the output stage as opposed to your first question saying the second stage Ok such errors happen so moving on to the output stage see http://www.tubecad.com/2004/blog0016.htm

The primary method of rasing the output impedance of the plate is via positive feedback this is illustrated hear> http://www.gem.hi-ho.ne.jp/katsu-san...c/STC_MX_1.gif
From this supper triode page http://www.gem.hi-ho.ne.jp/katsu-san.../7044_eng.html
Also see http://www.gem.hi-ho.ne.jp/katsu-san...1_english.html
A cross-coupled diff input diff output is also illustrated http://www7.taosnet.com/f10/figure7.gif
 
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Nixie

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Well, in referring to fig. 6, I was interested in the triode/tetrode second stage as driven by the cathode follower input. I quoted this particular patent as the second and third stages essentially correspond to the website description (in the webpage, the first stage is replaced with White cathode followers, and there is only feedback signal and no input at e1, and the connection to the output stage is DC coupled with current mirror, and there is stuff on the secondary 119). Now, there's probably more to it, given a comment at audioasylum (http://www.audioasylum.com/scripts/t...ubediy&m=51536), but...

Now I have four specific questions, please:
a) About the cross-coupled phase splitter -- the way I understand it, a mere CSS loading the triode also has the benefit of appearing like infinite plate impedance, so what's the point of doing it the way in the schematic? The only thing I see is that the positive feedback from the third stage cathodes makes for very high gain, allowing very high feedback (and very high frequency problems from this are dealt with by the feedback from the output through capacitors 122). Can't such positive feedback be done without this third stage, saving on tubes and complexity?
b) Capacitors 104 can be replaced by DC coupling through level shifting such as by a zener(as in other figs in the patent); what about capacitors 123 -- given it's in a local feedback loop, it's still in the signal path; any way to do away with it?
c) What about using this configuration in an OTL amp? Adding a negative rail, the load could be connected between the output devices, like the balanced single ended Aleph-X amps. But what if the output was to be unbalanced? How would the third stage outputs be properly coupled to a single output device? I'm asking because I have specific applications in mind.
d) In an OTL, since there's no tetriary winding 120, where would the main NFB be sourced? And in a way so that balanced input can be done without input transformers -- where would the main NFB be injected?

Yeah, I edited this message like five times...
 
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