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Original Message
Re: My parafeed 300B prototype and questions
Posted by dead_SHORT on May 24, 2004 at 00:13:18:
Hi Tanker.
I use almost exactly the same circuit with the major difference being using a 6C45Pi rather then a 6SN7. My resistor values, choke loads and currents are different as a result. I bypassed the cathode-anode resistor (R2 in your schematic) of the driver tube with a 47uF film cap rather then the cathode-ground resistor (R3) as you did.
C2 is a 47uF as well and I got this value basically as I had this size of motor-run oiler on hand.
My ripple at the speaker terminals is 3.5 mV of mostly 60 Hz. The 120 Hz ripple is largely canceled by a Steve Bench type nulling circuit. This I can live with on my 94 dB Tannoys. Without the nulling circuit, I had ~8 mV hum which is perceptable to me.
For C3 I use a 4 uF 1000V oiler.
Regards, David