[Boatanchors] #44/47 Bulb replacement with LEDs

[Garey Barrell]

Al -

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
<www.k4oah.com>


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.
> 73,
> Al
>
> 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
>> <www.k4oah.com>
>>
>