[Boatanchors] #44/47 Bulb replacement with LEDs
k4oah at mindspring.com
Sat Feb 5 12:11:34 EST 2011
Correct, it will NOT reduce the current through the filament segment,
but it should not 'kill' the LED.
I'll watch for it!
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
Al Parker wrote:
> Hi agn Garey,
> I guess I said it wrong. I meant, won't the LED bulb not reduce
> the current in the filament as much, so the failure rate would still
> be almost as high.
> BTW, your CD arrived a cupla days ago,many thanks. Will send a
> new topic to you later.
> On 2/5/2011 11:03 AM, Garey Barrell wrote:
>> Al -
>> Apparently the filament will carry the full 150 mA through that tapped
>> section, rather than the ~75 mA it sees with a parallel #47. I suppose
>> the higher failure rate of this filament section in radios run with
>> blown bulbs could be coincidental, but I've replaced a LOT of 34W4 and
>> 35Z5 rectifiers in my life, and most of them had a blown bulb and Pin
>> 4-6 (or 2-3) open.
>> It makes sense that the entire filament would be able to handle 150 mA,
>> but without a bulb that filament section is dissipating a little over 1W
>> and with a bulb a little less than 1/2W, not counting the DC current
>> which also goes through the filament. So without a bulb that section
>> would be the most likely to fail. Of course these were both very
>> inexpensive tubes, and a bulb or even a resistor cost money in a VERY
>> price competitive market.! :-)
>> As for the original question, if the LED was of the AC/DC types, it
>> should work fine. The voltage across the tap is 7.5 V with NO parallel
>> load and as long as the LED will handle that voltage it should be ok.
>> 73, Garey - K4OAH
>> Glen Allen, VA
>> Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
>> and TR-4/C Service Supplement CDs
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