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Old 15th Dec 2018, 3:22 am   #25
Argus25
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Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
Default Re: More Chinese AM radio kits

There is one thing to watch out for on all these transistor radios that use the red slug oscillator coils.

There are many of these red top coils that look identical from the outside and have the same application in MW band AM transistor radios. Wouldn't you know it, there are two types. One has the phase of the windings reversed. So if it is put in a radio pcb or wired up for the other version, there are no oscillations.

A lot of radio kits or other circuits using these coils get built and the constructor doesn't know why the the kit won't work and the transistor often gets blamed.

The suppliers for these coils, eBay or elsewhere never know which version they have. The only way is to test them. I had not known this until recently, having used these many times in the past, even in my childhood making AM radios, until I built a circuit with two VFO's using these coils and I got a bunch of them from a few suppliers. It was a big surprise to me that there where two types and it explained why I had read about troubles with kits using these coils.
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