Dumble Slidewinder?

[Fischerman]

I wonder if Frost just got the two mfr. names reversed. Maybe he meant that the Marshall needs a lower cathode resistor? It's all somewhat dependant on the tail resistor since all the current (which is determined mostly by the cathode resistor value) goes through the tail to 'lift' the whole PI.

So in a Marshall with a 10K tail you need a good amount of current to get enough voltage drop across that 10K...so 470 works well. In the Fender with a 22k tail you need less current to get a similar voltage drop across that 22k...so 820 works there. Yea...there were PIs over the years that used all sorts of combos but that's my take on it. I've been meaning to get some 680 ohm resistors just for PIs because it's often the perfect Rk value.

Also, I've hypothesized for the longest time that Fender designed the BF PI to work with a 12AX7. Just look at the values...they SCREAM "designed for a 12AX7". But then somebody stuck a 12AT7 in there and said; "Oooooh...it's cleaner...and cleaner is better." and they just used the 12AT7. It wasn't until CBS came along that they optimized the circuit for the 12AT7 (the one with 47k plates, 330k PI grid loads, etc.). The CBS amps get poo-poo'd a lot but some of the stuff they did was good. And that PI was one of them imo. Can't tell you how many times somebody 'Blackfaces' their SF amp...but it sounds worse. All imo.

[Fischerman]

And I even checked to make damn sure it hadn't already posted.

[jelle]

Also, I've hypothesized for the longest time that Fender designed the BF PI to work with a 12AX7. Just look at the values...they SCREAM "designed for a 12AX7". But then somebody stuck a 12AT7 in there and said; "Oooooh...it's cleaner...and cleaner is better." and they just used the 12AT7. It wasn't until CBS came along that they optimized the circuit for the 12AT7 (the one with 47k plates, 330k PI grid loads, etc.). The CBS amps get poo-poo'd a lot but some of the stuff they did was good. And that PI was one of them imo. Can't tell you how many times somebody 'Blackfaces' their SF amp...but it sounds worse. All imo.

I have been thinking the same for years!