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previous: Bruce q{P.P.S. Your suggestions about kee... -- 7/23/2000 4:11 AM View Thread

Re: ... latest revisions (7/20)

7/23/2000 11:08 AM
Steve A.
Re: ... latest revisions (7/20)
Adding in the crossline 150k resistor and 1200pF mica cap right where the output coupling caps go to the grid stoppers seems to work much better than the other tweaks I had tried...  
By that you mean the 47pF through 470pF shunting cap I assume...
    For starters, yes! Ahead of the PI I was running the signal through a 1M resistor to ground followed by a 100k grid stopper... with the idea being to keep the ac voltage on the EL84's down to a reasonable level.  
    When I first wired up the Version 2A Express preamp to the cathodyne PI and EL84 output pair the sound was way too bright and harsh; it was when I rewired the EL84's as quasi-triodes that I was finally getting some great sounds out of the amp. The posts here warning me about the high currents being drawn in the triode mode persuaded me to seek another solution... :o    At this point, I'm running the EL84's mainly as fixed-bias pentodes, so I've dumped a lot of treble and gain along the way... like the 1MA pot instead of a 1M grid resistor on the first stage (which I usually set to about 4 or 5). Adding the 250pF mica caps across the plate resistors for the second and third stage. And adding a 100k grid stopper going into the second stage grid (your suggestion if I remember correctly).  
Steve Ahola  
P.S. I don't have the formula handy... what is the RC filter created by the 150k/1200pF couplet? And with it located across the two phases the resulting frequency response curve would be inverted- right? (At least when compared to the signal running through the RC network...)

eric steve, how do you like this compare... -- 7/23/2000 11:26 PM
Bruce The RC (150K/1200pF) circuit's freq... -- 7/24/2000 6:14 AM