Putting a 3 pole Low Pass in a Foreplay
This is an example only, it has not been tested!
This involves working with high voltages, attempt this at your own risk.
Added 4/28/01 Updated 4/28/01

As a rough estimate R4, R5, R6 need to be between 40K and 200K.

R6 should be >40K because the 12AU7's plate resistance is 20K at the Foreplay's bias levels.
When you calculate the response of the circuit, use 20K in parallel with 120K + R6 for the actual value of R6.
If R2 is a C4S, use 20K + R6 for the actual value of R6 in the filter equations.

The upper limit of 200K is to keep leakage currents under control.

C2, C2, C3 should be rated for at least 150V.

First version Apr 28 2001 Last change 4/29/01. 
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