[R-390] Re: LED lamp replacement

[JamesMiller]

I prefer the "soft" on and off times of filament lamps over the
instantaneous on-off of LEDs.  My filament dial lamps sort of "ramp up" when
they come on, which is the true behavior that should be observed in this
genre of radi?  .  Ever drive behind a car with those obnoxious LED brake
lights, especially the Cadillacs?, They flash on instantly... no soft warm
up time.  It's grating on the nerves.

----- Original Message ----- 
From: "John Kolb" <jlkolb at cts.com>
To: "Tom Norris" <r390a at bellsouth.net>
Cc: <R-390 at mailman.qth.net>
Sent: Wednesday, July 07, 2004 1:26 AM
Subject: Re: [R-390] Re: LED lamp replacement


>
> 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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> >
>
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