[Boatanchors] #44/47 Bulb replacement with LEDs
anchor at ec.rr.com
Sat Feb 5 11:55:25 EST 2011
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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