On 2015-Dec-24, at 1:58 PM, Jon Elson wrote: > 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.
Similarly, I've replaced Ge with common Si in repairs of 60s-era discrete-component equipment and had no problems.
