Heatsinking the LM3886

[Brymus]

Hi yet another 3886 question...
I read a thread here that pretty well detailed the options of heat sinking the 3886 chip
Except for a couple of things I would like to clear up before going further.

Is a TO220 insulator big enough (or should I say wide enough)for adaquate thermal transfer?
I have a couple of TO220 mounting kits w/the Mica insulators and was hoping to use that.
It just doesnt quite cover the whole surface to be sinked.

And what do you guys use for mounting these audio chip amps?

Like as in part #s and source I found some Keystone Mica insulators but the one with the largest surface  area was the TO220.

[J M Fahey]

I use a TO218 mica (the one used by Tip142/IRFP250/etc.)
I use it sideways, covering perfectly the metallic part of the tab, with only 2 minor problems: 1) a new 4mm hole has to be punched , and: 2) The original hole leaves a small area uncovered, but since it´s on the "frontier" between metal and plastic, I have never had any problem so far.
Another option would be to reclaim a piece of mica from, say, a clothes iron heater, and cut/punch it to size.
Of course nothing beats getting the original correct part, but I'm so used to having to improvise Saturday nights, when Murphy's Law orders stuff to break, just before the show, that I've gotten used to it.

[Brymus]

Thanx JM
I searched the Mouser cataloge (I have hard copy)
And T0-220 largest size I could find.
Where do you order your insulators from?
And do you know of a supplier of just a small sheet of Mica?

I was thinking of cutting two small strips off of another TO220 mica insulator,...
But was afraid the cuts would distort the edges so as to make the thermal transfer less efficient and negate the benifits. any thoughts?

Also the thermal compound I have from Radio Shack says it has a dielectric rating of 300V
isnt that sufficiant for the small area where the insulator isnt covering? given the small gap and no actual contact?

I know 4 more questions
But I do appreciate the advice JM its has been very helpful as always.