Cathodyne PI?

[Dingleberry]

Hi.
I'm finally doing final tweaks to my 5F11-style scratch build clone.
I'm using dc-biased cathodyne (aka. Paul C-mod) at the moment.
Which is the correct way to install a grid stopper in the cathodyne?
Schematic 1 or schematic 2?

-T

[roberto]

Schematic 2: mount the grid stopper directly on the socket.

[rdjones]

Hi.
I'm finally doing final tweaks to my 5F11-style scratch build clone.
I'm using dc-biased cathodyne (aka. Paul C-mod) at the moment.
Which is the correct way to install a grid stopper in the cathodyne?
Schematic 1 or schematic 2?

-T

#2.
The grid stopper needs to be right on the grid pin terminal.

On the Sunn amp I added the grid stopper to, the cathodyne is the triode half of a 6AN8 being driven by the pentode, direct coupled.
I used "only" 270k.
Careful DC measurements before and after revealed only a very small (about 2V) difference in DC operating point.
I probably could have gone higher on the resistor.

rd

[gingertube]

The triode section of a 6AN8 is a low mu triode designed to run at quite high currents. That suits a HIFI Amp quite nicely but is not really the best for a guitar amp. You want to emphasize some of the cathodyne overdrive warts by using a high mu triode. I've had good success with 6SL7.
Cheers,
Ian