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Old 14th Apr 2019, 8:08 am   #138
Argus25
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Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,329
Default Re: More Chinese AM radio kits

Quote:
Originally Posted by Tully Bascombe View Post
Another kit to add to the collection, the RW08-7B, one I haven't seen before.

The circuit looks like the HX108-2 but the addition of a headphone socket and power LED.

The case is similar to the ZX2051 with the batteries side by side rather than either side of the speaker.
Unfortunately the circuit is really badly designed by a person with a limited knowledge of transistor design and who hasn't bothered to read Horowitz & Hill.
You will notice stages V2 and V5 with grounded emitters and base bias resistor to the power rail. Their circuit function and the collector currents are very dependent on the hfe of individual transistors that varies wildly among specimens. So the radio would work ok with transistors with just the right hfe, but if its too low or high then radio will not work or malfunction.
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