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RE: Scott 233 tube recomendations

Posted by Eli Duttman (A) on June 27, 2008 at 17:47:53

In Reply to: RE: Scott 233 tube recomendations posted by Mark W. on June 26, 2008 at 21:33:17:

Mark,

Refer to the schematic again. Please notice that the OEM values for the caps. (C16/C17) coupling the phase splitter to the "finals" is 0.1 μF. That's fine, when the 7591A grid leak resistors are 470 KOhms. Unfortunately, that value is too small in combination with the essential 270 KOhm grid leak resistor value. Deep bass performance is adversely affected.

Mere age made the coupling caps. candidates for replacement. Electrical reality demands the change. Use 600 WVDC/0.22 μF. 716P series Orange Drop parts in those coupling cap. positions.

C14 combines with R26 to form a high pass filter that's outside the NFB loop. Decreasing the value of C14 to 0.01 μF. will keep infrasonic noise out of the power amp section, which protects the O/P trafo against nasty sounding core saturation. Soviet surplus paper in oil (PIO) parts are a good choice here, as NFB will not cause sonic homogenization.

Eli D.

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