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In Reply to: RE: Question for Banat posted by Lew on February 18, 2014 at 18:55:30
"Circlotron often baffles me, I admit, but I see the PS capacitors as being in parallel with the output, not in series. You may say that this is a distinction without a difference. I wouldn't know until I try it."
I would say that, roughly speaking, the upper half of the audio waveform passes through one of the power supplies, and the lower half passes through the other power supply. (With a relatively minor amendment to that statement, since there will be some lesser amount of quiescent current through each set of tubes at the cross-over point in the waveform.)
In any case, if you trace the current through the loudspeaker, tubes and power supplies, it is evident that whatever audio current passes through each set of output tubes passes also through the power supply connected to their anodes (since it can go nowhere else). So if it is agreed that the audio signal is passing through the output tubes, then it must necessarily also pass through the corresponding power supply.
Chris
Follow Ups:
That seems correct and logical.
But the issue you raised is whether that 1000uF capacitor bypassing the cathode resistor has a topology identical to or different from that of the PS capacitors, with respect to the signal. I suggested that the PS capacitors "look" to me to be in parallel with the signal, whereas the proposed cathode resistor bypass cap is in series. I am not in a position to argue, I just want to know whether I am right or wrong in thinking that way. That is, I want to learn something.
(By the way, I hope we all agree that the term "cathode resistor" is not used in the conventional sense of the term; the signal is taken from the distal end of the resistor, at the ground potential of the PS that serves that side of the circuit, not from the junction of the resistor with the cathode of the power tube. The resistor is there just to promote current sharing among the output tubes.)
Lew
Yes !, by Circlotron OPS PSU C`s are definitive in Parallel with load(speaker)! , but cathode(s) res. bypass C`s are definitive in Series with load(speaker) !
( That`s can easy open new `playground` for probes & experimentation with different sorts, brands names and values for Rk bypass Elko`s :), but it is relative easy now since this cathode bypass C`s are relative available & cheap.)
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Enlightened Evolution-Astral Projection
"Yes !, by Circlotron OPS PSU C`s are definitive in Parallel with load(speaker)! , but cathode(s) res. bypass C`s are definitive in Series with load(speaker) !"
I don't agree. Look at the schematic; the upper pair of tubes, the supply B1 and the loudspeaker are all connected in *series*. Likewise, there is a second series-connected loop comprising the lower pair of tubes, the supply B2 and the loudspeaker. One of those loops predominantly handles the upper half of the audio waveform, and the other loop predominantly handles the lower half of the waveform. In each case the corresponding power supply is in series.
(The discussion is slightly complicated by the fact that each set of tubes conducts for rather more than just its half-cycle of the waveform, but this is inessential to the key point.) If we consider the bulk of the audio waveform, away from the crossover region, either one set of tubes or the other is passing the overwhelming portion of the current. We then have a simple loop, comprising the speaker, the set of conducting tubes, and the associated power supply, all in series.
One wants, for example, that the two power supplies should have as small an impedance at audio frequencies as possible. If the capacitance of the filter capacitors was too small then the output impedance of the power supplies would rise significantly at the lower frequencies and there would be a loss of low-frequency audio output, exactly as would happen with any situation where a capacitor is in series with the speaker.
Chris
FWIW, what you say is consistent with my experience: the more PS capacitance, the better the bass response, subjectively.
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