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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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13th May 2022, 6:36 am | #1 |
Hexode
Join Date: Jan 2011
Location: Düsseldorf, Germany.
Posts: 367
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Germanium transistor replacement
Hi,
I saw this interesting message but I like to know how the story continues. 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
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13th May 2022, 8:53 am | #2 |
Hexode
Join Date: Jul 2004
Location: Paris, France
Posts: 346
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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 |
13th May 2022, 10:30 am | #3 |
Moderator
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,787
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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. |
13th May 2022, 11:33 am | #4 |
Nonode
Join Date: Aug 2015
Location: Cambridge, Cambs. UK.
Posts: 2,196
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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
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13th May 2022, 11:41 am | #5 |
Moderator
Join Date: Jun 2003
Location: Oxford, UK
Posts: 27,787
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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.
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13th May 2022, 12:17 pm | #6 | |
Dekatron
Join Date: Dec 2007
Location: Haarlem, Netherlands
Posts: 4,185
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Re: Germanium transistor replacement
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13th May 2022, 12:31 pm | #7 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,801
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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
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13th May 2022, 6:01 pm | #8 |
Nonode
Join Date: Jun 2007
Location: Coulsdon, London, UK.
Posts: 2,152
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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. |
19th May 2022, 2:48 pm | #9 |
Hexode
Join Date: Jan 2011
Location: Düsseldorf, Germany.
Posts: 367
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Re: Germanium transistor replacement
Many thanks to all for your inputs!
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
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