Question for tube aficionados

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

Raindance 3-16-2018
They are also prone to oscillation with the wrong tube choices because of CJ's refusal to follow good design practice and use grid stopper resistors.

Interesting point, which I hadn't been aware of.  I couldn't find a schematic for the PV11, but I took a look at schematics for the PV10 and PV12 which are available at HiFiEngine.com.  And I can confirm Raindance's assertion for at least most of the tube stages in these designs.  I have no idea why CJ wouldn't have put grid stopper resistors having at least relatively low resistances into these designs, but as Raindance indicated not including them is definitely not good design practice.

The following article provides good background on this subject, even though it is oriented toward guitar amp applications:

http://www.aikenamps.com/index.php/grid-resistors-why-are-they-used

Regards,
-- Al
 

Hi RV,

First, I note the following statement in the manual for the PV11:

It is well known that tubes of a given type vary sonically depending on the manufacturer. We have chosen the brands of tubes we supply based on extensive auditioning of available brands. The choice of brands has been made solely on the basis of sonic performance without regard for either cost or prestige. We know of no vacuum tubes available which will improve the sonic performance of your PV11....

... Please note: The indiscriminate substitution of type 12AX7 tubes for the 5751 will seriously degrade the sonic performance of the unit.

Also, apparently four of the six tubes in the PV11 are used in its phono stage, and only two in its line stage. And I would not necessarily assume that a given tube is likely to exhibit similar behavior in the two kinds of applications.

Given all of that, it may be worthwhile contacting CJ and asking if they can tell you what tubes were originally used in the PV11.

Beyond that, FWIW like some of the others I have had fine results with Gold Lion reissue 12AX7 and 12AU7 tubes, in my case in line-level and driver stage applications in a Chinese-made Paxthon integrated amplifier I used for a while some years ago. They handily outperformed a number of vintage tubes I also tried in that amp, including some vintage Telefunkens which go for considerably higher prices.

Good luck. Best regards,
-- Al