Advice with germanium transistors

[Bill Coleman]

On May 18, 2004, at 9:28 PM, Doug Shields wrote:

> Hello all,
>       I have done a lot of design with transistors and integrated
> circuits
> but not with germanium parts.  I just got a "working" Heathkit IP-27
> power
> supply and found two of the three germanium power transistors are
> shorted
> (collector to emitter.)    Replacement germanium parts are available
> but
> VERY expensive.  I have thought about replacing them with modern
> silicon
> power transistors.  What should I watch for in the conversion?  Any
> help
> from the real semiconductor gurus out there?  Thanks very much.

I am NOT a semiconductor guru, but the key difference between germanium
and silicon components is the voltage drop across a PN junction.

Silicon devices will drop anywhere between .6 and .8 volts, with the
typical value being .7. Germanium, on the other hand, has a much lower
threshold - about .3 to .4 volts. So, those germanium pass transistors
may be designed for much less than a 1 volt drop at full rated voltage
and current. You won't be able to do that with a silicon device.

Depending on the raw supply voltage before the regulator, you may run
out of regulator headroom with silicon devices sooner than germanium,
because of the difference in voltage drop -- so your ripple could
increase at higher voltages and/or currents.

Some of these ancient germanium devices may be prevalent in old junk
boxes. You might want to check for them at hamfests and swapmeets.


Bill Coleman, AA4LR, PP-ASEL        Mail: aa4lr at arrl.net
Quote: "Not within a thousand years will man ever fly!"
             -- Wilbur Wright, 1901

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