On 12/24/2015 01:22 PM, Jay Jaeger wrote:
On 12/24/2015 9:59 AM, Michael Thompson wrote:
We have been able to fix all types of broken flip-chips. Sourcing the
components is sometimes a challenge. The Germanium transistors for the TU20
on the PDP-9 were hard to find.
I remember replacing a germanium (at least I think it was) transistor on
an SMS card with an ordinary silicon transistor in a 7094-II floating
point unit back around 1974. Luckily, that worked fine, though for a
museum I imagine one would prefer to use the "real thing". ;)
Yes, I overhauled an old HP digital frequency synthesizer
that was all built out of PNP Germanium transistors (no
ICs.) I substituted the first one with a VHF Silicon
transistor and did some tests on the bias, etc. and was
pleased to find it was a total drop-in replacement. I
replaced over 10 of them in that unit, and they all worked
flawlessly.
I can imagine some difficult circuits where you couldn't get
away with this, maybe a magnetic read amp or a timing
circuit or something, but I think in most cases a Silicon
transistor will work well.
Jon
