PI grid stoppers?

[MHProd]

Is it worthwhile to install let's say a 5K6 or 6K8 or more on the PI grids to prevent oscillations or blocking distortion?

Anyone has experience with this?

[Gaz]

Assuming Long tail pair, yes, you can do it, and go way higher too (e.g. 47K-100K). It could help with blocking, but probably isn't necessary. On a cathodyne it's needed to get rid of the nasty raspberry sound (which I actually like to a certain extent), and 500K to 1M is more typical. The Vale Wizard (Merline Blencowe's) preamp book has a lot more info on that.

[roberto]

Yes, the reason why you can raise by one order of magnitude on the cathodyne, without affecting the high frequencies, is that gain is (less than) one, so miller effect is way lower.