[Boatanchors] #44/47 Bulb replacement with LEDs

[Garey Barrell]

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>


Al Parker wrote:
> Hi folks,
>     In the AA5 or 35W4 application, aren't we missing one of the 
> purposes of the lamp?  It provides a load to balance out the voltage 
> wanted across the tube filament.  An LED lamp is much lower a load, in 
> the neighborhood of 10%, so it's not going to serve that purpose.
> 73,
>
> Al, W8UT
> www.boatanchors.org
> www.hammarlund.info
>
> "There is nothing -- absolutely nothing -- half so much
> worth doing as simply messing about in boats"
> Ratty, to Mole
>
> On 2/5/2011 10:07 AM, Michael A. Bittner wrote:
>> Chuck, Thanks for the info and data sheet on the 35W4. Looks like it's
>> OK to use the 35W4 in a series string without harm as in my Knight Ocean
>> Hopper and according to the alternate diagram on the data sheet.
>> This still leaves us with the question of how one of these #47 bulb LED
>> substitutes would work in an AA5 radio. After all, the D in LED stands
>> for diode. W6MAB
>>
>>     ----- Original Message -----
>>     *From:* Chuck <mailto:wcmoore at verizon.net>
>>     *To:* infomet at embarqmail.com <mailto:infomet at embarqmail.com>
>>     *Cc:* boatanchors at puck.nether.net 
>> <mailto:boatanchors at puck.nether.net>
>>     *Sent:* Friday, February 04, 2011 9:45 PM
>>     *Subject:* [Boatanchors] #44/47 Buld replacement with LEDs
>>
>>     The 35W4 is a bit of a strange bird. The filament is tapped but
>>     rather than
>>     being tapped at the center like the venerable 12AU7 and similar
>>     valves the
>>     35W4 is offset so that there are different drops across each
>>     filament section.
>>      From Pin 3-4 with a #47 Lamp the filament drop is 32 Volts. From
>>     Pin 4 - 6
>>     the nominal drop is 5.5 volts.
>>     For more info see the datasheet at the follwoing URL:
>>     http://www.r-type.org/pdfs/35w4.pdf
>> > Great question......thanks, Mike!
>> > 73....Walter - K5EST - Missouri
>> >
>> >
>> > On Thu, Feb 3, 2011 at 7:39 PM, Michael A. Bittner wrote:
>> >> How would these work in an AA5 radio where the #47 bulb is often
>> >> connected
>> >> across one half of the rectifier heater? Rectifiers are
>>     typically 35Z5 or
>> >> 35W4 with center-tapped heater. Mike W6MAB
>> >
>> > _______________________________________________
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>>
>>
>>
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