What kind of final should this radio have in it?

[nomadradio]

So this was gonna be another "what's wrong with this picture", showing a 2SC2166 driver and a counterfeit 2SC1969 final transistor together on the heat sink of a Galaxy DX2547 radio.

Bobbled the file transfer, lost that shot.

The point was to show how to tell that the bipolar transistors in this radio are not the right ones to use. Don't know who installed the older bipoar parts, but there was no chance for them to work in this unit. This radio had the switchmode power-supply "brick" in it. Those appeared when the radio was redesigned for lead-free, and to use the IRF520 MOSFETs as driver and final transistors. That alone should have been a clue.

Here's the bias trimpot for the driver transistor. Marked "104". Like the three color bands on a fixed resistor, this is a 100,000 or 100k ohm trimpot.

The older bipolar driver transistor would have a 1k trimpot marked "102".

And the final stage has the same thing.

The original bipolar bias trimmer pot would have been marked "201" or "501".

Don't know if this question will ever fall into your lap, but if you find yourself wondering whether the radio is built to use the older bipolar driver/final or the current-day MOSFETs, this is the quick answer. Just look at the bias trimpots.

73

 

[Handy Andy]

R244 right next to it, is another strong clue - don't get too many Bipolar Biasing schemes using a 47K Resistor

They seemed to have used it's 1/2W package for the purpose of looking into those bins and - "Oh here's one!"

 

[nomadradio]

I think the half-Watt package for R244 has more to do with the spacing between its mounting holes. The part used for biasing the bipolar transistor needed the higher Watt rating, was either 150 or 180 ohms IIRC.

But RCI was stuck with that lead spacing, probably would cause the insertion machine a headache trying to stretch a smaller part across those two holes.

73