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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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Originally Posted by ricard View Post
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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Old 6th Oct 2019, 11:48 am   #25
Paulus.d
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Default Re: Tandberg series 12

I've put this machine away as after changing all the transistors and electrolitic caps the channel 2 amp is still completely silent .. just touching the imput spade connector doesn't produce any hum .. it still requires another r/pb head as i'm swapping it out of my Series 15 to test it.
The channel 2 record/ play switch does not make the recording indicator light upand there are many signs that this machine has been worked on before...
Ill come back to it later on.....
Regards Paul
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