[georgetownjohn]

Phorum members, I am trying to find the bulb # for PHILCO Shadow Meter part number 45-2180 that is from a 37-640 chassis. regards--John

[RodB]

Any 6.3 volt pilot light will work. I would use the brightest one I could find in my workroom. Be sure the dial is clean, don't use water to clean it. Use odorless mineral spirits and soft cotton, be gentle. The dial is printed with water based ink.

[GarySP]

Not sure if anyone has tried this but there are 6.3 volt miniature lamps in bayonet and screw-in base options available on Amazon and others. A lot brighter than incandescent and easier on the PT load-wise, but was wondering if the replacement would introduce RF noise. Not very expensive if one wanted to 'experiment'. Take care and BE HEALTHY! Gary

[morzh]

Gary

I doubt it would introduce any noise. We use similar lamps for the panel indication, 12V AC lamps: they are LEDs with a diode and a resistor. No active circuitry. And because there is no inrush (no capacitors) there should be little to no noise; not anymore than you would have from a regular lamp.

I have not seen these with active circuitry: this, given the size, price etc would be a waste.

[RodB]

I did try an LED bulb in place of the original but wasn't impressed with the amount of light on the dial. Seems like it was too wide.

[RossH]

Butting in here with a question. Since the shadow meter is connected directly to the 1st and 2nd I.F.'s wouldn't the meter need the current limiting effect that an incandescent provides, or am I offbase?

[georgetownjohn]

I think after all has been said, I will use the same bulb that is specified for the dial pilot light which is a #55.
I have ordered the slotted mask for the Shadow Meter face(opening). Does anyone know if there should be
any type of lens or cover on the mask opening.

[morzh]

Ross


I am not sure what current limiting effect the incandescent provides.
They are two different parts of the schematic.
The meter is just that, a meter, and the bulb is just that, a bulb, and is fed by simple AC transformer winding, often in parallel to the filaments.

[RodB]

Mike is correct on the bulb connection, two separate circuits. I found that by rotating the bulb and sliding it forward or backwards you can adjust the display.

[RossH]

Ok. Thanks for the correction.

[Arran]

Now if you had a set with a tuning light then the bulb type is important to the circuit, some sets used those prior to the Magic Eye craze, which our beloved Philco never got into, they stuck with the shadow meters until 1938.
Regards
Arran