02-11-2007, 12:29 PM
I get -8V at point B, and 55V at points C. The 55V at the C's seems ok (current of the 71A's (2x18mA) on [1400 + 187 = pins 1-2 + 2-3 of the multiresistor 25]Ohm). So, B should be at 187/(1400 + 187) = 12% of 55V = 6.5V.
Chris-
I don't have a 20 to make references from, so I can't add much more than this:
The grid voltage is often measured with respect to the cathode and something around -55v would sound right for the grid of a 71-A with plate at 300v. 71-A's are not meant to have this plate voltage.
I suggest you back your filter caps back down to 8 or 10mfd per section. 20 is way too much and will raise your B+ too high; if you have excess hum later, you can experiment with bigger caps. In other words, make it play first.
Chris-
I don't have a 20 to make references from, so I can't add much more than this:
The grid voltage is often measured with respect to the cathode and something around -55v would sound right for the grid of a 71-A with plate at 300v. 71-A's are not meant to have this plate voltage.
I suggest you back your filter caps back down to 8 or 10mfd per section. 20 is way too much and will raise your B+ too high; if you have excess hum later, you can experiment with bigger caps. In other words, make it play first.
Pete AI2V
