Spent all week-end taking that old Rochar counter to bits, what a job... it's built like a tank... I pity anyone having to actually fix or restore these things... they aren't meant to be worked on....
Anyway, just found this thing : on the power board, the big T03 pass transistor is obviously mounted on a heat sink and what did they use for thermal transfer to the H/S ? Paste ? Mica ?
Obviously not silicone as it's too old... no, none of that ! It's something new... new to me at least. Never even heard of it.... look at it !
A thick pad made of..... LEAD ?!

It sure looks like it to me ! It's made of metal, it's ductile, you can shape it effortlessly to whatever shape you want, doesn't kink, doesn't crack... it's like putty.
Qualities you would want for a H/S pad I guess !

I will try not to lick it, don't want to get some nasty disease.... not that I lick mica pads either, mind you...
Anyway that was quite surprising and educational so I thought I would share !
Do old beards here remember such things ??