When I ordered transformers for my Fi Primer L-W Jack at Electra-Print gave me this mod. He said the amp would be sensitive to tube variations; well guess what, he was right. Swaping 2A3's from left to right channel makes little or no difference, however when swaping 6SL7's the voltage variations simply move to that channel. Despite ordering matched 6SL7's, there's still a 2ma difference between 2A3 bias current. I'd like to get the channels closer than that, so I've ordered 6 more matched & balanced 6SL7's & am hoping will find two which will be a better match. If that doesn't pan out, then I may decide to try this mod. Wondering what the EE's think of the mod? The original circuit uses a 390K 2A3 grid resistor in place of the 47K in drawing........ & the original circuit uses a 820 ohm resistor in place of the 100 ohm pot & 750 ohm resistor (replaces 820 ohm middle resistor in string)
I later added the volume control as the amp has more than plenty of gain for a CD player. After using this amp for several weeks now & despite the minor fiddling around, I still feel it's one of the best sounding amps (if not the best) I ever had & I've had (& still have) quite a few including OTL, SET as well as the usual PP SS & tube amps.
I later added the volume control as the amp has more than plenty of gain for a CD player. After using this amp for several weeks now & despite the minor fiddling around, I still feel it's one of the best sounding amps (if not the best) I ever had & I've had (& still have) quite a few including OTL, SET as well as the usual PP SS & tube amps.
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