Assymetrical caps on PI

[greiswig]

Hi,

I notice a lot of PI designs have different sizes of capacitor feeding each half of the PI. Like .1uF on one half, .02uF on the other. Why is that?

[ChrisM]

The 0.1uF is there to block DC voltage. Often times builers will use a cheap cap there because it has no real affect on tone.

The decoupling capacitor for the second grid (Cg2) must pass all frequencies to ground (down to 1Hz ideally), and can be found in exactly the same way as the input capacitor, although the fairly universal value of 100nF is usually suitable. In this case it will decouple down to 1.7Hz, which is sufficient.

More info here
http://www.freewebs.com/valvewizard/acltp.html

[greiswig]

I see...so I was looking for symmetry where doesn't need to be. Thank you!

[Drumslinger]

Good reading, thanks Chris.

[iknowjohnny]

The 0.1uF is there to block DC voltage. Often times builers will use a cheap cap there because it has no real affect on tone.

The decoupling capacitor for the second grid (Cg2) must pass all frequencies to ground (down to 1Hz ideally), and can be found in exactly the same way as the input capacitor, although the fairly universal value of 100nF is usually suitable. In this case it will decouple down to 1.7Hz, which is sufficient.

More info here
http://www.freewebs.com/valvewizard/acltp.html

I think it will affect tone if you have NFB.

[Richie]

Depends on PI used too, an 18 watt marshall doesn't have FB, and each side feeds each channel, so the caps will make a difference in the tone depending on the cap value used. I think your question is more related to wreck, and most marshal,l fenders, and others.