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Aiken "Long-Tailed-Pair" Article Q's

3/6/2000 4:10 AM
Morris
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Aiken "Long-Tailed-Pair" Article Q's
I'm in the process of building an amp with a Fender blackface-style preamp (using a 6SL7 instead with a 250p/.02/.02 tonestack) and a 2x6V6 output section. I was going to use a 2xEL84 output section but the guys here thought my PT might be a little stiff for that (it's a Hammond 270FX, 275-0-275). I plan to run the 6V6's in UL with no negative feedback (except for the UL of course). My last problem is the resistor/cap values in the PI, which will also be a 6SL7. I read the great article on the "long-tailed-pair" at Randall Aiken's site but I still had one question. He states:  
 
"If no global negative feedback is used, the tail resistor should be made as large as practical, with respect to the amount of current being drawn, and the desired headroom of the amplifier. This will give the best balance to the PI outputs. This resistor has little effect on gain, but a major effect on balance and headroom."  
 
OK, I don't have a scope, so could anyone help me with some ballpark values for the tail resistor in a ZNFB configuration like the one I have? Actually, help in deciding the best resistors/caps to use throughout the PI for the amp I have would be greatly appreciated.  
 
Thanks in advance for your help!  

 
Replies:
Randall Aiken Aiken "Long-Tailed-Pair" Article A's -- 3/6/2000 7:04 AM