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Author Topic: TR4-C light bulbs out  (Read 6843 times)
K3WEC
Member

Posts: 260




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« on: December 14, 2013, 02:50:31 PM »

The bulbs that illuminate the front panel went out all at once.   Radio works fine other than this.   The bulbs aren't burned out.  Something in that circuit is afoul.   Any obvious ideas on what could be the problem?  I'm simply not qualified to troubleshoot.   
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WD8AJY
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Posts: 60




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« Reply #1 on: December 15, 2013, 08:58:34 AM »

Check the lights switch on the back.

73 Bob WD8AJY
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K3WEC
Member

Posts: 260




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« Reply #2 on: December 15, 2013, 12:26:15 PM »

I did that first, should have mentioned it.  No go...
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W0BTU
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Posts: 1719


WWW

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« Reply #3 on: December 15, 2013, 12:48:21 PM »

The lamps are in series. That's why they both went out at once.
Schematic at  http://www.oocities.org/drake_tr_4/Drake_tr4_esquema.gif

Best to replace them both at once, the good one will likely soon follow.
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N4NYY
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Posts: 4800




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« Reply #4 on: December 15, 2013, 03:52:19 PM »

The lamps are in series. That's why they both went out at once.
Schematic at  http://www.oocities.org/drake_tr_4/Drake_tr4_esquema.gif

Best to replace them both at once, the good one will likely soon follow.

In addition to Mike's great info, the #47 bulb has a hi durability variant, and I cannot recall what the number is (1847 maybe?). The ciruit is just a 12.6V tap. If the filaments are lighting in the tubes, the voltage is there for the bulbs.
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KD0REQ
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Posts: 972




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« Reply #5 on: December 15, 2013, 06:28:11 PM »

1847 is the bulb, they are 5000+ hour rated per Sylvania.  assuming they are on AC, with DC applied miniature lamp filaments develop thin spots from the continued one-way shock.  what our Chinese friends are doing with them, don't know, but should be the last bulbs you ever put in that radio.  get two sets, just in case, as you best do with all filamentary hollow-state things these days.
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W9GB
Member

Posts: 2626




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« Reply #6 on: December 16, 2013, 05:13:06 PM »

The #755 incandescent bulb has a 20,000 hour life (last your lifetime usage).
2 bulbs for $1.50 USD
http://www.2bradioparts.com/page22.html

(Something to think about)
When replacing the old 6V #47 dial /meter lamps you might want to  
consider replacing them with the longer life (#755 Bulb)
The #755 has about 5~6 times the life of the original #47 bulb and is almost as bright.

(See comparison specifications below)

#755 Bulb Specifications
(Longer Life Replacement)
Lamp Size  T3-1/4
Volts 6.3V
Current 0.15 Amp
M.S.C.P.  0.33
Average Life 20,000 Hours
===
#47 Bulb Specifications
Drake Factory Original Bulb
Lamp Size  T3-1/4
Voltage 6.3V
Current 0.15 Amp
M.S.C.P  0.50
Average Life 3,000 Hours
===
#1847 Bulb Specifications
Lamp Size T3-1/4, Miniature Bayonet Base (BA9S)
Voltage 6.3 Volt
Current 0.15 Amp
M.S.C.P.  0.38
Average Life 5,000 Hours
Filament Design C-2R
===
Incandescent Bulbs?

BULB TOWN - Jacksonville, FL
http://www.bulbtown.com
« Last Edit: December 16, 2013, 05:25:57 PM by W9GB » Logged
N4NYY
Member

Posts: 4800




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« Reply #7 on: December 16, 2013, 05:34:49 PM »

The #755 incandescent bulb has a 20,000 hour life (last your lifetime usage).
2 bulbs for $1.50 USD
http://www.2bradioparts.com/page22.html

(Something to think about)
When replacing the old 6V #47 dial /meter lamps you might want to  
consider replacing them with the longer life (#755 Bulb)
The #755 has about 5~6 times the life of the original #47 bulb and is almost as bright.

(See comparison specifications below)

#755 Bulb Specifications
(Longer Life Replacement)
Lamp Size  T3-1/4
Volts 6.3V
Current 0.15 Amp
M.S.C.P.  0.33



Nice !
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W8AAZ
Member

Posts: 348




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« Reply #8 on: December 17, 2013, 04:14:14 PM »

Can you extend bulb life with a little bit of series fixed resistance, some compromise value that does not dim it to the point of uselessness but still reduces the current through the bulb?  It is not like a tube where emission/function is an issue if the filiment voltage is too low.
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KB1NXE
Member

Posts: 347




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« Reply #9 on: December 18, 2013, 11:28:13 AM »

Digikey and Mouser both sell LED direct replacements for type 47 bulbs.  Just do a search on the respective site for "LED Replacement Type 47 bulb"
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K3WEC
Member

Posts: 260




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« Reply #10 on: December 19, 2013, 07:24:13 PM »

Thank you all!  I am ordering the replacements tonight.  
« Last Edit: December 19, 2013, 07:33:00 PM by K3WEC » Logged
N4NYY
Member

Posts: 4800




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« Reply #11 on: December 20, 2013, 05:12:55 AM »

Thank you all!  I am ordering the replacements tonight.  

I would go with the long life bulbs W9GB posted.
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