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previous: Josh I am trying to figure out what valu... -- 8/22/2000 5:43 PM

Re: cap value for cathode-bias amps

8/23/2000 4:47 PM
Dave H.	Re: cap value for cathode-bias amps Last time I worked it out 250/10 came to 25 not 12 Making the impedance of the cap 1/10 the impedance of the resistor will bypass the resistor for AC signals but you need to know the lowest frequency of the signal because the impedance of the cap is 1/2piFC. The lowest note on the guitar is ~80Hz so you need a cap C=1/(2piFR) or 1/(2pi8025) = 80uF but 22u sound good to me with 250 ohms and 2 x 6V6s. Why not try 250u and 25u and a few values in between and then fit the value that sounds best to you. The theory is OK but it doesn’t beat tweaking and listening. Dave

8/23/2000 4:47 PM

Dave H.

Re: cap value for cathode-bias amps

Last time I worked it out 250/10 came to 25 not 12

Making the impedance of the cap 1/10 the impedance of the resistor will bypass the resistor for AC signals but you need to know the lowest frequency of the signal because the impedance of the cap is 1/2piFC. The lowest note on the guitar is ~80Hz so you need a cap C=1/(2piFR) or 1/(2pi*80*25) = 80uF but 22u sound good to me with 250 ohms and 2 x 6V6s. Why not try 250u and 25u and a few values in between and then fit the value that sounds best to you. The theory is OK but it doesn’t beat tweaking and listening.

Dave

Replies:

Josh yes, you are right. I had the numbe... -- 8/24/2000 3:25 AM