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Old 24th July 2015, 11:33 AM   #1
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Default Pegeant AV-126-TR Projector

HI,

I am working on the audio circuit of this very, very old projector. My concern are the 2 power transistors. They are 2N307, a TO-3 germanium power transistors. When tested base to emitter and base to collector forward bias, they read about 10 ohms. When tested reverse bias, they read about 3K ohms. When tested collector to emitter both ways, they read about 600 ohms. Are these low resistance readings normal for germanium power transistor or are the transistors leaky. I am not familiar with germanium power transistors. I am also unable to find a suitable replacement. Can someone please help.

Thanks

Carlos
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Old 24th July 2015, 12:37 PM   #2
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That sounds about right to me. They are normally slightly leaky with a 0.4V junction voltage unlike 0.7V for silicon.
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Old 24th July 2015, 12:56 PM   #3
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Originally Posted by JonSnell Electronic View Post
That sounds about right to me. They are normally slightly leaky with a 0.4V junction voltage unlike 0.7V for silicon.
Thanks, JonSnell, I will try out the transistors and let you know.

Carlos
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Old 25th July 2015, 11:36 AM   #4
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Thanks, JonSnell, I will try out the transistors and let you know.

Carlos

Hi,

I put in the transistors and tried. There is sound but distorted. It cannot be the capacitors as I have changed all the capacitors on the board. The only problem is that the values are not exact. Like I replaced the 60uf with 56uf, 75uf with 68uf, 25uf with 22uf and so on, all within the 20% range. I have tested the small transistor and resistors as well and they are OK. One of the power transistor seems to get hotter and faster than the other. These PNP transistors are totally obsolete. Can I use a silicon PNP transistor as a replacement. Will the circuit work. Please advice.

Thanks

Carlos
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