Purpose of these resistors and caps...

[Rogue]

I tried to search but wasn't sure what they are called, so nothing came up. This was posted in the fender forum, and I've seen them in other circuits as well.

http://ampgarage.com/forum/download/file.php?id=41581

V1B, V4A and V4B all have resistors (rather large value) and capacitors bypassing the grid to the plate. I've seen bypass caps, either to the B+ side of the plate resistor or to ground, used for either HF attenuation or oscillation, or both. I'm not sure if these serve the same purpose or not. I'm guessing it is the same result, but I don't know. But the large value resistors in series with the caps makes it even more a question mark as to what they actually doing.


What's the purpose of this setup?

Also on V1B, it's a 22M, a cap, and another 22M. Any reason the cap is sandwiched between the two?

thanks!

[roberto]

Grid stoppers, they cutoff highs together with Miller capacitance.

The 22M plus cap is local feedback.

[Rogue]

Ah, thanks Roberto.

Wouldn't all three be a local feedback circuit then? And I assume they would be negative feedback, right?