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Valves / Vacuum Tubes
Armstrong A220 design questions
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<blockquote data-quote="Ampdog" data-source="post: 803535" data-attributes="member: 144"><p>Concurring with compliments uttered in the previous post.</p><p></p><p>This post: What dof questions, El Sid? (You are confused by other posts - oops!)</p><p></p><p>The design uses the classic paraphase phase inverter (an unfairly criticised topology in some quarters, I might add). But firstly, may we rename the "leftmost R15' rather R13? - I do not find an R13 and from the print that "5" might well be a "3". I will thus refer to it as 'R13' further on. </p><p></p><p>The classic paraphase topology consists of R14, R15 around V7b. (For those not familiar, R14 and R15 are normally equal or near so in value. This creates anode-grid unity feedback. It thus follows V7a providing a balanced inverted signal via V7b to the power stage, therefore the name 'paraphase'.) The vaues are quite high so as not to have an effect on the load resistors of R9, R10. Remember they are feeding a valve grid as input which has very high impedance if relevant at all (one often sees 5-meg resistors there). The only limitation really is that imposed by bypassing stray capacitance and the anode-grid capacitance. (It is a very good topology - provided the designer knows his job!)</p><p></p><p>Hope this helps. </p><p></p><p>When we come to R13, that is an extra voltage feedback over V7a.</p></blockquote><p></p>
[QUOTE="Ampdog, post: 803535, member: 144"] Concurring with compliments uttered in the previous post. This post: What dof questions, El Sid? (You are confused by other posts - oops!) The design uses the classic paraphase phase inverter (an unfairly criticised topology in some quarters, I might add). But firstly, may we rename the "leftmost R15' rather R13? - I do not find an R13 and from the print that "5" might well be a "3". I will thus refer to it as 'R13' further on. The classic paraphase topology consists of R14, R15 around V7b. (For those not familiar, R14 and R15 are normally equal or near so in value. This creates anode-grid unity feedback. It thus follows V7a providing a balanced inverted signal via V7b to the power stage, therefore the name 'paraphase'.) The vaues are quite high so as not to have an effect on the load resistors of R9, R10. Remember they are feeding a valve grid as input which has very high impedance if relevant at all (one often sees 5-meg resistors there). The only limitation really is that imposed by bypassing stray capacitance and the anode-grid capacitance. (It is a very good topology - provided the designer knows his job!) Hope this helps. When we come to R13, that is an extra voltage feedback over V7a. [/QUOTE]
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Audio and Video Talk
Valves / Vacuum Tubes
Armstrong A220 design questions
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