[R-390] Re: LED lamp replacement

[John Kolb]

While there may be a possibility of RFI generated by the
LED's or (blasphemy) solid state diodes, I'm more curious
about the light output. The light out of LED's is rather
directional - how well do they work in the R-390?

John

On Tue, 6 Jul 2004, Tom Norris wrote:

> I have not noticed any noise since replacing the bulbs with
> LEDs. I think I even put the scope to the line feeding them
> as this was mentioned before on another list a while back.
> My dial light replacements are fed with a series resistor
> followed by a diode, followed by two LEDs in series. There
> is a 1 mf cap in parallel with the pair of LEDs. There are
> now three junctions in the mix and the possibility of
> noise either by radiation or by propagation along
> the filament line. I may simply have overlooked any
> noise, I may not have actually been looking for it.
> I honestly don't remember, I've slept since then.
>
> Maybe a study is called for here, when I do the LED's
> on the current room-strewn receiver, I will make and
> record actual noise/ripple measurements.
>
> But before the RX gets done, I have to reassmble the
> Johnson Valiant, and before it gets done, I have to
> put a Transworld back together, so it may take a while.
>
> 73
>
> Tom
>
>
>
> >Instead of LED's, best bet is probably the long-life version of the standard
> >replacement bulb.  I think there's a reference on it and some list members
> >may know offhand what the number is.  As I recall, there is quite a bit of
> >difference in the hours spec. and not that much difference in price.
> >Brightness may be a bit lower, though.
> >
> >Anyone know?
> >
> >Barry
> >
> >----- Original Message -----
> >
> >
> >>  Hi
> >>
> >>  If you do that then you have two items to worry about. The LED's have a
> >>  reverse breakdown voltage and you now have a half wave rectifier. That
> >>  gets you right back into the chopped current = RFI problem.
> >>
> >>  If you run them in reverse parallel pairs then the breakdown voltage is
> >>  not an issue but you still only run current through them when the
> >>  voltage is above about 1.6 volts on the diode. Off of a 6.3 volt AC
> >>  supply having no current for 1.6 volts is a fairly large amount of
> >>  chopping. You are right back to the RFI issue.
> >>
> >>  I know all this sounds a bit like witchcraft but the R-390 is
> >>  particularly vulnerable to the problem. The designers simply never
> >>  considered there would be a source of broad band RFI *inside* the
> >>  radio. The other gotcha is that it is such a sensitive radio that you
> >>  can hear crud with it that other radios would simply miss in the noise.
> >>
> >>  Take Care!
> >>
> >>  Bob Camp
> >  > KB8TQ
>
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