wrote:
What I consider the better TO-3s are aluminum, not steel.
** Though once common, Aluminium TO3 paks are no longer used by most manufacturers due to problems with thermal expansion of the aluminium base causing microscopic cracking of silicon chips.
Thermal expansion of aluminium is about 7 times greater than that of silicon, limiting the number of full thermal cycles such devices were good for.
https://www.engineeringtoolbox.com/t...als-d_859.html
Steel and copper alloy packs are used instead, with most having a "coin" made of a metal with intermediate rate of expansion soldered between the chip and the pak.
Another advantage is that they won't bend as much if the mounting
surface is not perfectly flat.
** Yuck. Better use only flat heatsinks.
..... Phil