[R-390] Re: LED lamp replacement

[Tom Norris]

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