Pilot lamp blows out - Printable Version

Pilot lamp blows out - Printable Version

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Pilot lamp blows out - Buzz - 10-16-2013

Hi Gang:
I am restoring a Philco Model 51-537 Clock/Radio Model.
All the caps were replaced, resistors checked, and replaced when out of spec.
The radio worked, so I proclaimed it finished. Then I installed the pilot lamp, and it seemed to blow out at various stages...sometimes during warmup, after warm-up, sometimes after minutes. Icon_sad

.....the radio will still play good.
How do I troubleshoot this? The radio uses a 35Y4 rectifer tube , and the lamp is wired to pin 1 and pin 4. The lamp socket measured 10.6 VAC and 2.35 VDC when warmed up.
Any ideas out there?
Thanks,
Buzz

RE: Pilot lamp blows out - Radioroslyn - 10-16-2013

Two things come to mind. Bad rectifier tube or wiring/socket on lamp. Lamp can't be grounded.
Terry

RE: Pilot lamp blows out - BrendaAnnD - 10-16-2013

Clean the socket for the 35Y4 thoroughly. If there's a tiny bit of oxidization on the tube pins or the socket, the pins are loose, it can cause this.

RE: Pilot lamp blows out - Buzz - 10-16-2013

Is the 10.6 VAC too high? Isnt it suppose to be about 4 volts.. its a #47 lamp.
I'll clean the rectiifer tube, also have ordered a new one,,
will let you know..
thanks
Buzz

RE: Pilot lamp blows out - LASJayhawk - 10-16-2013

Do you have the correct pilot lamp installed?
Keep in mind that with most sets using that tube, the plate current flows through the dial lamp (and hopefully the resistor in parallel with the lamp) SO if the radio is pulling too much B+ the pilot lamp will blow.

Tube datasheet: http://tubedata.milbert.com/sheets/049/3/35Y4.pdf

It's about the same thing as a 35Z5, so this page from Chucks site might be of interest as well:

http://www.philcorepairbench.com/tips/svctip40.htm

RE: Pilot lamp blows out - Buzz - 10-17-2013

Hi:
Using a #47 bulb per schematic.
My schematic has no resistor in parallel.
Do you think I should add one?
Phil's tips say to use a 300 ohm 5 watt resistor.
thanx,
Buzz

RE: Pilot lamp blows out - LASJayhawk - 10-17-2013

I don't think it's a bad idea. A bad pilot light can damage the tubes filament, and then it will start taking out pilot lights. The resistor protects the tube from the burnt out light and stops the chicken or egg thing from starting in the first place. I would change the tube at the same time as it is now suspect assuming you've tried cleaning the socket and pins on the tube as B.A.D. suggested.

The 10 vac is your filament voltage from the heater string and should be around 3 or 4 volts IIRC. The 2.3 vdc is the plate current of your B+ being dropped across the light bulb.

RE: Pilot lamp blows out - Buzz - 10-21-2013

Update on the Philco 51- 527 clock/radio.
Received a new 35Y4 rectifier tube.
Installed the tube and hooked up meter to measure voltage.
Everything worked, and the lamp voltage settled at 4.3 volts.
Ran a few hours and still ok.
Installed the 300 ohm resistor across the lamp, just in case.
Still works good so I'm declaring this puppy restored. Icon_clap

Thanks to all..
Buzz

RE: Pilot lamp blows out - Randy H. - 11-12-2013

LASJayhawk
Change the rectifier tube. (35Y4, 35Z5, 35W4) This was a very common failure mode. The 'Dial Lamp' tap on the tube filament opens up, and the lamp pops. Then the SET won't work. I've changed hiundreds of them. BTW... Good idea to replace the lamp, as well.