]I would be concerned aboot that connecting the two transistor cases both thermally and electrically in a manner that affects the deliberate isolation provided by that BeO disc. ![Shocked :o](https://www.eevblog.com/forum/Smileys/default/xshocked.gif.pagespeed.ic.CrwtrNUjLO.png)
mnem
![Tweak :-/O](https://www.eevblog.com/forum/Smileys/default/smiliey_cal.gif.pagespeed.ce.yYMcAvxBJk.gif)
Gorilla glue is an insulator.
Nevertheless I should check they aren't somehow electrically connected.
For some value of "insulator". We're talking about a 200G
input here, so what counts as an insulator by normal experience may not count as an insulator in this particular application. However, if memory serves this is a long tailed pair and if the cases are going to be connected to anything internal to the transistors it's going to be the 'common' side of the long tailed pair where the circuit is only going to have something between a few ohms and a few k ohms between the two devices so the leakage from a 1G
'short' between them isn't going to matter more than a fart in a hurricane.
What is your opinion aboot the change in mass of the junction? It seems to me the BeO disc was chosen for both thermal conductivity and electrical insulation properties...
mnem
![Confused :-//](https://www.eevblog.com/forum/Smileys/default/confused0024.gif.pagespeed.ce.5xOqKkq0Co.gif)
The whole point of the assemblage is to keep the two transistors as near the same temperature as possible to keep input offset voltage from the temperature sensitivity of V
BE as close to fixed as possible. Any changes here are going to affect offset voltage and offset voltage drift with temperature. The offset voltage can be trimmed with the front panel offset pot, drift is minimised by maximising the thermal coupling of the two transistors. That this comes with a
front panel offset adjustment suggests that the whole thing was not Mr. Stable in the first place so there's clearly no long term 'baked in' stability to worry about. With that in mind, going to the expense and trouble of a BeO washer attached to the
tops of the cans in hoping to replicate a
monolithic matched pair (that's how it's drawn so we must presume that at some point in its production history there really was a monolithic matched pair there) with just a matched pair smacks of magical thinking.