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 Post subject: Philco 48-460 -122 dial bulb burn out problem
PostPosted: Sep Mon 05, 2011 6:02 pm 
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Hi all,
I recently started to rebuild a Philco 48-460 radio that i found on the side of the curb. I replaced all of the paper and electrolytic caps in the unit and tested the tubes. When I fired the unit up on my variac, it powered up and i got a very nice sound and no other problems. I let it run for an hour and every thing worked fine. I turned the unit off to clean up a bit of rust and when I fired the unit back up, the dial light burned out. I replaced it with a new unit and the same problem occurred. The schematic calls for a 6.3v .150A Ge47. I've tried a Ge 44 as well with the same results. If i bring the unit up with the variac, it will stay alive. Is there a way to limit the inrush current/voltage to the bulb or maybe something i may have missed. The bulb is in line with the 35Y4 heater tap.
Thanks,
Brandt

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 Post subject: Re: Philco 48-460 -122 dial bulb burn out problem
PostPosted: Sep Mon 05, 2011 6:14 pm 
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Location: Indiana
some put a small resistor in series with the bulb to help , most the time I find something wrong with rectifier tube or filament circuit, you might look at some other radio's schematic to see how they are wired to fix problem

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 Post subject: Re: Philco 48-460 -122 dial bulb burn out problem
PostPosted: Sep Mon 05, 2011 7:31 pm 
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When bulb stays alive--what is final variac output voltage to the radio and is this less then line voltage ?
When bulbs died, did they die immediately upon turning on switch, early in tube warmup, late in tube warmup, generally when ?


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 Post subject: Re: Philco 48-460 -122 dial bulb burn out problem
PostPosted: Sep Mon 05, 2011 7:44 pm 
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The final voltage on the variac is 121 same as my line voltage. The bulb dies instantly when the unit is first turned on

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 Post subject: Re: Philco 48-460 -122 dial bulb burn out problem
PostPosted: Sep Mon 05, 2011 9:37 pm 
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Quote:
I turned the unit off to clean up a bit of rust
Did you make sure you got rid of all the little flakes and maybe steel wool particles? they can reek havoc.

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 Post subject: Re: Philco 48-460 -122 dial bulb burn out problem
PostPosted: Sep Mon 05, 2011 10:50 pm 
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Joined: Apr Fri 03, 2009 10:32 am
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Location: New Rochelle, NY
In that model, dosen't the dial indicator move along with the two wires leading to the bulb?
1) Look for a open cut or open wire exposure with the two wires. Check the connections for each wire.
2)When the light bulb is working jiggle the pilot light wires.
3) Check the casing in which the #47 bulb is seated.
I have encountered this problem a number of times, once this year.
The most simplistic reasons should be looked for, first.


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 Post subject: Re: Philco 48-460 -122 dial bulb burn out problem
PostPosted: Sep Mon 05, 2011 11:32 pm 
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Brandt

Could the lamp tap be open on your 35Y4?

A lamp may be ok when the radio is brought up slowly on a Variac. It will burn out with a turn on surge unless the 35Y4 lamp tap section is good. Check filament continuity on 35Y4 between pin #1 and #8, pin each side of keyway.

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 Post subject: Re: Philco 48-460 -122 dial bulb burn out problem
PostPosted: Sep Tue 06, 2011 12:22 am 
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this is what I thought it maybe bad rectifier tube

Norm Leal wrote:
Brandt

Could the lamp tap be open on your 35Y4?

A lamp may be ok when the radio is brought up slowly on a Variac. It will burn out with a turn on surge unless the 35Y4 lamp tap section is good. Check filament continuity on 35Y4 between pin #1 and #8, pin each side of keyway.

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 Post subject: Re: Philco 48-460 -122 dial bulb burn out problem
PostPosted: Sep Tue 06, 2011 12:53 am 
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I double checked the chassis and wiring for shorts and found none. When I get back home, I'll check the rectifier tube filiment section. I did check the schematic and found that the tube filaments would work without the bulb in it and they are not pointing to a possible bad rectifier tube. Looks like the bulb is completing the string. Thanks for all the input.

Brandt

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 Post subject: Re: Philco 48-460 -122 dial bulb burn out problem
PostPosted: Sep Tue 06, 2011 1:03 am 
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Here is the circuit for others to view:

http://www.nostalgiaair.org/PagesByMode ... 013634.pdf

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 Post subject: Re: Philco 48-460 -122 dial bulb burn out problem
PostPosted: Sep Tue 06, 2011 2:14 am 
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My tube tester has a test to check both sides of the filament. It can be open on one side and still put out enough emission to test ok. That's the most common reason for pilot lamp failure in AC/DC radios.


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 Post subject: Re: Philco 48-460 -122 dial bulb burn out problem
PostPosted: Sep Tue 06, 2011 6:16 am 
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Location: Livermore, CA
Some tube testers only check between tap and one side. This can miss an open. All a tester really has to do is check overall filament, forget the tap. If the overall filament is ok the tap will also be good...

For 35Y4 it's pin 1 and 8. 35Z5 pin #2 and 7 34W4 pin #3 and 4.

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 Post subject: Re: Philco 48-460 -122 dial bulb burn out problem
PostPosted: Sep Tue 06, 2011 6:57 am 
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If you have a heater-cathode short : Looking at the diagram, the almost-full line voltage will be on the bulb when the filter capacitors charge instantly in parallel with the other tube filaments.

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 Post subject: Re: Philco 48-460 -122 dial bulb burn out problem
PostPosted: Sep Tue 06, 2011 8:26 pm 
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Ok, found that one side of the heater connection was open on the 35y4 as all expected, ordered a new tube and a thanks again to everyone here for their help.
Brandt

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