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Determining the size of inter-stage coupling cap

I'm trying to understand the determination of an appropriate sized cap for a cap-coupled SET. Working with Paul Joppa's update on Joe Roberts' WE91 300B, the schematic shows C7=0.1uF and R10=390k. Using the formula f=1/(2Pi*R*C) am I correct that this results in a corner frequency of 4.14Hz?

I also found Al's thread about replacing R10 with a choke that has the impact of changing R10 to 250k (http://www.audioasylum.com/cgi/vt.mpl?f=magnequest&m=11930). If I incorporate this change with a pair of nice NOS oil caps that measure 0.25uF, am I correct that this shifts the corner frequency to about 2.6Hz (and keeps phase shift below 26Hz)?

Am I calculating things correctly here? Does making this change result in any negative impacts that I am not considering?

Thank you for any input!

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Topic - Determining the size of inter-stage coupling cap - EricSan 18:24:42 01/22/17 (11)


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