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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 7th Aug 2019, 1:38 pm   #21
TIMTAPE
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Default Re: Tandberg series 12

I probably mentioned this before but when I worked for a company servicing Phillips dictation gear we had those Germaniums regularly break down. We discovered it was always a "base to case" short and I think we ended up placing an insulating washer between the case and the chassis, or something like that.

With the Tandberg machines of my own or a customer's I've used the same idea, this time cutting the copper heatsink plate vertically down the centre, separating each transistor's case from the other while still maintaining the heatsinking. It was a resignation to the likelihood the "whiskers" would only reform at some stage, apart from the scarcity of such Germaniums new these days.
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Old 7th Aug 2019, 3:34 pm   #22
ricard
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Default Re: Tandberg series 12

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Originally Posted by TIMTAPE View Post
I probably mentioned this before but when I worked for a company servicing Phillips dictation gear we had those Germaniums regularly break down. We discovered it was always a "base to case" short and I think we ended up placing an insulating washer between the case and the chassis, or something like that.

I wonder if that's because the base in these transistors is actually a large (-ish) slab of germanium, compared to the other electrodes which are small 'lumps' on the base substrate, so the likelyhood of a 'base to case' short is much higher than for the other two electrodes.
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Old 8th Aug 2019, 8:36 am   #23
Paulus.d
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Default Re: Tandberg series 12

Had the amp working for about 10 seconds!!!! then silence again...
I'll look for a complete new set of transistors for it....
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Old 8th Aug 2019, 12:32 pm   #24
TIMTAPE
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Default Re: Tandberg series 12

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Quote:
Originally Posted by TIMTAPE View Post
I probably mentioned this before but when I worked for a company servicing Phillips dictation gear we had those Germaniums regularly break down. We discovered it was always a "base to case" short and I think we ended up placing an insulating washer between the case and the chassis, or something like that.

I wonder if that's because the base in these transistors is actually a large (-ish) slab of germanium, compared to the other electrodes which are small 'lumps' on the base substrate, so the likelyhood of a 'base to case' short is much higher than for the other two electrodes.
Thanks Ricard, interesting and plausible idea.
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