RCI 39VHP anyone know bias settings?

[Low_Boy]

Kind of a odd ball it looks like 2,13N10's driving 2, RT1 transistors. Whatever a RT1 is?

 

[Eldorado828]

I've asked that question myself on that specific radio. I can tell you that the rt1 is a irfz24npbf. Why they thought to call it their own (rt1) who knows.

 

[Low_Boy]

I see where they ground off what ever was on the final and put RT1 over it.

 

[Enterprise312ok]

3.5 to 3.7 volts on the gate makes a happy rt1 most of the time. Match a perfect pair of fets and no magic smoke most of the time.

 

[brandon7861]

3.5 to 3.7 volts on the gate makes a happy rt1 most of the time. Match a perfect pair of fets and no magic smoke most of the time.

Setting bias by voltage might not be a good idea. I don't know about those particular mosfets, but i have seen 520's have very different Vgs values. A small voltage difference makes a huge current difference.

Set bias by drain current or using a spectrum analyzer.

 

[brandon7861]

Find your largest spurious emission (not harmonic) and adjust bias to minimize that peak.

 

[Enterprise312ok]

Probably not the best way, the jumper arrangement in these radios is not Ideal for measuring current. The typical 50-70ma on the drivers and 100ma on the matched pair of finals.
When ranger used to publish service info they specified voltage on the am only models so many techs use voltage on the Conex style radios. I am sure a current or spectrum analyzer setting is superior but unlikely on an am radio.

 

[brandon7861]

Probably not the best way, the jumper arrangement in these radios is not Ideal for measuring current. The typical 50-70ma on the drivers and 100ma on the matched pair of finals.
When ranger used to publish service info they specified voltage on the am only models so many techs use voltage on the Conex style radios. I am sure a current or spectrum analyzer setting is superior but unlikely on an am radio.

You don't need jumpers, just run the radio on a bench supply with a current meter. Turn the driver and final off by dropping the gate voltage, then slowly raise the bias until the appropriate current change is noted on the supply's current meter.