[R-390] LED lamp replacement

[Bob Camp]

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



On Jul 6, 2004, at 11:10 AM, Don and Diana Cunningham wrote:

> The truly nice thing about LED's is that you don't have to convert AC 
> to DC
> to run them (or am I missing something, after all, they ARE 
> diodes????).
> 73 all,
> Don, WB5HAK (lurker)
> ----- Original Message -----
> From: "Bob Camp" <ham at cq.nu>
> To: "Tom Norris" <r390a at bellsouth.net>
> Cc: <R-390 at mailman.qth.net>
> Sent: Tuesday, July 06, 2004 9:49 AM
> Subject: Re: [R-390] LED lamp replacement
>
>
>> Hi
>>
>> Well I guess I run the risk of getting thrown off for mentioning this
>> but the issue with the LED lamps is more or less the same as some of
>> the solid state ballast replacements. (duck and run for cover ....).
>>
>> When you convert AC to DC to run the LED's the current is only going 
>> to
>> flow in short little pulses when the AC waveform is higher in voltage
>> than the DC turn on point of the LED. The pulsing of the current
>> creates noise clear up into RF. The R-390 was not designed to be
>> shielded against this sort of thing going on inside the radio.
>>
>> If you decide to go the LED lamp route I would suggest that a separate
>> wire routing power for the LED's would be a good idea. Then come up
>> with as quiet an AC to DC conversion as possible and stuff it off in
>> the power supply module. At least that way it's as far from the IF and
>> RF as possible. Just for the record, yes I stole that idea ....
>>
>> The nice thing about the LED's is you can get an awful lot of light 
>> out
>> of them these days. I have an R-1051 with an LED conversion in it that
>> works very well.
>>
>> The illumination angle coming out of an LED is more narrow than the
>> angle of light coming out of the bulbs we normally use. One solution 
>> to
>> this is to do violence to the front end of the LED. The other is to 
>> run
>> multiple LED's. If you get your DC off of the 25 volt AC line then you
>> can put quite a few LED's in series ....
>>
>> Since the bulbs for the 390 are still commonly available and fairly
>> cheap I'm not sure I would do all this work on a 390. If and when the
>> bulbs get into the $40 a bulb category like the R1051 bulbs then we'll
>> have a bulb replacement thread on here that goes on and on forever.
>>
>> Take Care!
>>
>> Bob Camp
>> KB8TQ
>>
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>