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In Reply to: RE: Take a look at this Cary SLP-90 schematic posted by Michael Samra on November 13, 2014 at 17:38:31
Michael, I'm sure you were thinking of something else, but the 22K resistors are power supply dropping resistors and are decoupled from the tubes' plates via the 470uF caps. If you can measure the current draw of these tubes you could then substitute both 22K resistors with Hammond's 153-159 series chockes that have the appropriate current rating. These will most likely end up being somewhere in the range of 15 to 30H and in addition they're small and inexpensive units.Because the chokes' DCR values will be a lot less than the resistor values, you would then need to adjust the PSU's voltage by properly sizing the first cap. My guess for this would be anywhere from .22uF to 2uF. If you could measure the transformer's off-load voltage and DCR values at the rec sockets (with no tubes in), you could design a nice power supply having the desired output voltage in PSUDII. If and when you take said measurements, you could post them here and perhaps we could help a bit too. If not, we'll still be very interested in whichever way you decided to go.
Edits: 11/14/14Follow Ups:
I think the biggest improvement you could make would be to directly couple the preamp stages.
After that, use all that excess voltage to build a regulated B+ supply.
You might also try not having parallel triodes up front.
The paralleled triodes on the CF and paralleling them raises the transconductance and halves the output impedance.I thought about using one triode in the CF but I hate having one nonfunctional.
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Paralleling the voltage amp halves doesn't really do anything beneficial.
How about paralleling 3 of the triodes for the cathode follower.
The two triodes in the CF if the line stage are already paralleled..Where are you getting a 3rd CF section? I agree that I haven't heard much sonic benefit to the paralled triode.
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Edits: 11/14/14
The voltage amp section also has paralleled triodes.
Yes but that isn't a cathode follower tho.
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Yes, there are four triodes per channel. Two are voltage amps, two are cathode followers in the stock circuit. As a mod, you could take one of the voltage amp triodes and add it as another cathode follower triode.
Wouldn't I lose gain tho?
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No. If you removed one of the parallel voltage amps, you'd double the cathode resistor and plate load. There would be no loss of gain.
Thanks..When I saw the absence of the plate resistors on the paralleled follower,I somehow thought at glance that the PS resistors in that divider network acted as the load resistors...I like that idea that you've presented.
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