On Thu, 21 Apr 2011 21:15:25 +0100, Baron wrote:

josephkk Inscribed thus:

On Mon, 18 Apr 2011 17:36:42 +0100, Baron
wrote:

N_Cook Inscribed thus:

1.8mm slabs of porcelain under TO220 devices.

I would check that ! Its more likely that they are Beryllium_oxide !
http://en.wikipedia.org/wiki/Beryllium_oxide

Tried grinding a clearance notch on the side of one
pad but got nowhere as ceramic.
Not only that but I had no trouble holding the slab in fingers while
trying to grind a slot, it was barely getting warm - good thermal
insulator or small grinding wheel not generating heat as not cutting
into the material ?

The dust from grinding or abrading Beryllium_oxide is highly toxic !

BeO is very expensive. I would be very surprised to find any in such
application.

I wonder how much 12 dozen TO3 BeO insulators would be worth ?

The last time i saw a price they were over US $1 each, but that was over
30 years ago and for military use. Between the now rabid regulation and
the expected cost i would be rather surprised to find them in commercial
instrument amplifiers. Of course with Chinese manufacture such bets may
be knocked into a cocked hat.