I may be featuring a psychic hood in my game soon. I think true psychic hoods should be exceptionally rare, available only the the Adeptus Astartes and accomplished Inquisitors. As such, I'm not going to worry about things like price. I've been considering two major possibilities for the rules.

The psychic hood adds +2 to power rolls. In addition, any time another psyker manifests a power, the bearer of the psychic hood can try to nullify it. The psykers make an opposed WP test. If the psyker using the hood wins, the power is nullified and has no effect, aside from a possible flash or other neat effect as the warp power is dispersed.

The other possibility would be very similar. If the psyker with the hood wins the roll, the threshold for the power is increased by 10, and a further 10 (or maybe just 5) for every degree or success.

A couple of things I can't make up my mind on: Should psychic phenomena occur regardless of whether or not the power is nullified? I'm thinking yes.

Under the second method, should the psyker attempting the power be allowed to roll additional power dice (assuming he hadn't rolled all of them) after seeing the result of the WP test?

Thats a truly mighty item and i think its near unprice-able like some millions thrones
And i would renamed it to cowl/crown of psychic supremacy, hood just sounds to dull in my ears:P

To simplify things I think I'd just say the "hood" turns the person into a Blank, meaning no psyker powers go out and in. Rules for that was in the DotDG so that would make it a lot simplier.

Personally I agree.. rename it from Psychic Hood which sounds blah and Generic to something else. Maybe name it after a (small time local)Saint you create that was an infamous Blank who is said that a garment blessed in his name is infused with this same power.

Since a Cowl is a hood worn by a travelling monk, it would be a fitting name.

So for example

Saint Sarius' Cowl

-or-

Cowl of Saint Sarius

Maybe because he´s referring to the actual psychic hood thats rather infamous throughout warhammer fluff....

http://wh40k.lexicanum.com/wiki/Psychic_hood

Even if it wasn't already in canon, why the heck would it have to have some fancy, pointless name? Simple names are powerful ones. "Psychic Hood" invokes all kinds of ideas just as a descriptive term - why would you want to rubbish the emotive impact of that?

Yes, it is intended to be the same psychic hood that is established in the 40k background.

I don't feel the Null rules would be appropriate. I don't know if they're necessarily simpler, and I think it would dilute the flavor if these two very different objects/conditions had the same rules.

Ok
then id make an psy-jammer giving a +30( insted of +20) to resist psychic powers and the effect of pentagramic wards from DotG p.120
and if very generous i would allow the wielder to make an opposed invocation check against the enemy caster.
and the price will be so, that it can only be obtainable from i very few individials with a black market price ranging from 0.5million to 5 million thrones.