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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

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Old 26th Oct 2020, 9:21 pm   #1
BenHoper
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Default Bush TR82 - general transistor bias question

In the Bush TR82, in the pre-amp stage TR5, the voltage at the collector (output) is marked as 8.3V off a 9V battery.
Ref:
https://www.vintage-radio.net/forum/...3&d=1386851936

Why is that voltage so high? If you wanted a nice large clean voltage swing, surely you would have it closer to 4.5V?
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Old 26th Oct 2020, 10:40 pm   #2
Herald1360
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Default Re: Bush TR82 - general transistor bias question

It's because it's driving a transformer primary rather than an actual resistor. This means that the collector can swing dynamically as far above the 9V rail as it can swing down before it hits the emitter voltage level.

The transformer coupled output of a typical valve set behaves in the same way with the standing anode voltage sitting as near HT+ as the primary resistance voltage drop allows.
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Old 27th Oct 2020, 2:30 pm   #3
BenHoper
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Default Re: Bush TR82 - general transistor bias question

HERALD1360 thank you for the explanation, very helpful. I'll do some more reading on that. Thanks you.
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