Re: Adjusting pa bias (RV3) blows one of the final #ubitx


An indicator lamp (incandescent) is sufficient


On Fri, 29 Nov 2019, 17:18 Jerry Gaffke via Groups.Io, <> wrote:
Any particular "car lamp"?
There's headlights, tail lights, brake lights, dash lights, turn signals, ...
There's incandescent, halogen, LED, ...

My guess is that you are thinking of something like an 1157 incandescent light.

This has two different filaments, try the thinner tail light filament first.
If the voltage drops too much at the required current then try the thick brake light filament.
Could get a little bit more ummph by running both filaments in parallel.

Seems an incandescent light is well suited to this sort of thing since the resistance goes up drastically when it's hot.
So it has little effect at low currents, but severely restricts high currents.
An 1157 plus jumper cables to a 12v source is a quick and easy current limited power supply.
Assuming you are happy with a rough current limit of something under 1 Amp.

I have never tried it.

Jerry, KE7ER

On Fri, Nov 29, 2019 at 07:21 AM, Lawrence Galea wrote:
Apart from the suggestions by our friends, best is to use a current limited supply so that if it goes above the setting it will protect the set or use a car lamp in series with the supply which will also provide some protection.
As suggested a multi-turn pot is better to adjust the bias.
Happy weekend

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