Germanium transistor replacement
 

Hi,
I saw this interesting message but I like to know how the story continues.:shrug:

https://www.vintage-radio.com/repair...or-faults.html

Is there any list available how I can interchange old Germanium-type transistors?
What about the other BIAS when using Silicon transistors?
A general chart list will be fine.....;)

Happy weekend,
German Dalek :angry:

Re: Germanium transistor replacement
 

Hi to all,
Hi German Dalek,

An interesting series of chapters (look at upper right of home page) on replacing Germanium transistors with Silicon and the bias changes required for proper operation :

http://www.hawestv.com/transistorize...htm#conv_intro

Hope this helps with what you want to achieve,

Best Regards
jhalphen
Paris/France

Re: Germanium transistor replacement
 

In the majority of cases there is sufficient tolerance within the circuit and transistors themselves to operate without bias changes. Early Ge transistors had a wide spread of characteristics, and the circuits designed for them had to work with all of them.

The big exception is the audio output stage, which almost always requires circuit changes to work properly with silicon.

Re: Germanium transistor replacement
 

As an example, a couple of weeks ago I had to replace a dead AF117 frequency changer in my Bush TR130 transistor portable. The only PNP transistor I had to hand was a common-or-garden silicon BC214. It works fine. It of course ran at a lower collector current because of the higher Vbe of the silicon device, so I increased it by lowering the emitter resistor value. But that made no apparent difference to its performance.

Martin

Re: Germanium transistor replacement
 

I've also found the BC214 to be a reasonably reliable AF11x substitute, but I only use them because I bought a big bag of them for peanuts years ago so have hundreds of the things. Modern BC55xs or 2N3906s will probably work just as well. It's always worth trying whatever you have to hand.

Re: Germanium transistor replacement
 

While it can be useful to replace germanium transistors with silicon ones, especially in new builds, there's also an alternative. Since you're located in Germany, there should be plenty non-whiskery germanium transistors to choose from as non-Philips brands were quite popular over there. Telefunken and Siemens should be just fine. Also imported types from Tungsram.

Re: Germanium transistor replacement
 

There are quite wide spreads in transistor parameters, so in a lot of respects you can get away with murder. But the most dependable parameter is Vbe. Roughly assumed to be 0.7v for Silicon, and close to half that for Germanium.

Carefully designed circuitry takes into account fairly large variations in gain from device to device, but Vbe is taken as almost gospel.

Where things get difficult is in circuitry with either very low supply voltages, or with very crude bias arrangements. You need to look at the circuitry around each transistor being replaced to spot these cases and then consider bias resistor value changes. Most often, you can do the job by changing one or two resistor values, but you do need to check.

Silicon still has a significant sensitivity to temperature, but it's much tamer than Germanium, so substitution is often an improvement. In general temperature compensation with germanium transistors was a problem, and often not done, so you aren't likely to run into trouble with too little temperature sensitivity.

The current gains of some Germanium power transistors were somewhat better than many silicon types, so care is needed here.

David

Re: Germanium transistor replacement
 

I recently replaced a noisy OC71 (PNP) with a high gain BC558 (PNP) and changed one of the bias resistors. This is in a Decca TP85 (1963).

It works but needs adjusting. This first audio stage seems to have been originally designed for minimum current consumption. The emitter current is about 30 microAmps. The collector voltage is near Vcc and so there is not much room for voltage swing.

Leakage through the bypass capacitor which is across the emitter resistor, and leakage through stage coupling capacitors (electrolytic) can have a significant effect on the bias.

Re: Germanium transistor replacement
 

Many thanks to all for your inputs!:beer:
I shall work it out, will make a nice translation of it
and bring it to book standard.
The print-out will be saved.
Then I shall see, if I have more questions.

Best regards,
German Dalek :angry: