Question for tube aficionados

Yes, you can definitely do better that what you've been using. 

As a general note, please remember also that replacing a tube alone is not good enough. Compensating tube production variations, tube aging (and, especially, when using equivalent models) always demands a check and adjustment of bias voltage. I experienced surprisingly significant sound differences from the bias voltage differences of 5%. To make it more challenging, certain systems will benefit from setting a bias voltage that is different than the one recommended by the amp manufacturer. Additionally, my recent observation indicates that the replacing tubes and adjusting bias can also introduce embellishment and extension of trebles that can be easily taken for increased resolution while it only adds graininess.

Hi Folks...

Need to correct almarg and raindance about those grid resistors.  I was in touch with Jeff Fischel, now heading up c-j, about those PV-11 grid resistors.  Apparently the sources the previous posters used were wrong. Here is his reply to me:

"Bob,

 Actually on all 3 of these models we do employ grid resistors on all gain stages , typically a 47R5 resistor. All CJ preamps use grid resistors either 47R5 , 100R or 332R.

 Thanks,

 Jeff Fischel

conrad-johnson design inc.

703-698-8581

http://www.conradjohnson.com/"

Guess doing it correctly is one reason their equipment consistently sounds so good.

Actually on all 3 of these models we do employ grid resistors on all gain stages , typically a 47R5 resistor. All CJ preamps use grid resistors either 47R5 , 100R or 332R.

Thanks, Coppy. Good to know.

That information doesn’t appear to be consistent with the schematics I looked at for the PV-10 and PV-12 at HiFiEngine.com, and 47R5 (i.e. 47.5 ohms) seems much lower than usual for the value of a grid stopper resistor that would be effective in these kinds of designs. But in addition to the high confidence I would have in an answer provided by Mr. Fischel the bottom line would seem to be, as you said, that "their equipment consistently sounds so good."

Thanks again. Regards,
-- Al

I have no idea what you’re talking about, but I can tell you the preamp is terrific,
even after all these years!