Small cap to ground off rectifier socket??

I've been looking at some gut shots of an older Friedman Dirty Shirley, and I'm just wondering the purpose of the small film capacitor that's connected from pin 8 to ground off the GZ34 socket? I think it's .0047uf / 630V

It also looks like they put the standby switch between the rectifier and the first filter cap, which is a big no no.
Is the film cap related to that?
The Valve Wizard recommends a 47K / 2W resistor paralleling the standby switch if you do this filter cap arrangement. There is no resistor on this standby switch.

Just curious.
Thanks!

Small cap is to keep AC off of the cathode of the rectifier tube. Good grounding practice since B+ is used as small signal ground elsewhere in the amp. Extra cudos for attaching it directly to the pin of the tube for better harmonic stability/performance as stray lead capacitance can introduce problems.

Thanks for the info!
The pic is of a real Dirty Shirley, but I duplicated this in my clone build.
I also added safety diodes to the rectifier socket that the DS does not have.

fusedbrain":1w86xagz said:

Thanks for the info!
The pic is of a real Dirty Shirley, but I duplicated this in my clone build.
I also added safety diodes to the rectifier socket that the DS does not have.

Click to expand...

The safety diodes to the rectifier socket is a very good move too.