Rebuilding a nice 116B tombstone from 1935. It's playing nice and loud now, but the shadowmeter isn't functioning properly. The pointer/flag doesn't move at all. It has a part number of 45-2083.
I've read the page on the Philco tips section and I've watched John's Corner of the Deck You Tube video about restoring shadowmeters. He remagnitized the one-inch metal horseshoe in his. This unit doesn't have the larger horseshoe piece. The pointer flag appears to move between a much smaller mechanism. Don't know if you could even get a magnet into it. The coil reads about 540 ohms.
Anyone had experience with this type of unit? Thanks, John.
The coil is in place. Doesn't look to have been disturbed. Reading from the two leads coming out it measures 540 ohms on the multimeter. The lamp is working behind the meter. The 2,000 ohm resistor/shunt is OK. Since posting this I read that sometimes the pointer/flag gets stuck with age. Maybe that's worth checking.
540 Ohm indeed hints at the coil being OK though the mere fact of it "in place and not having been disturbed" means very little by itself - all bad coils I have seen were in place and undisturbed, and open.
In your case since it reads well below 2K we might assume it is the coil shunting the 2K resistor so it is likely good.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
I was able to remove the coil and shadow mechanism with kid gloves. I even attempted to magnetize the metal on each side of the pointer/flag. I also put a drop of WD-40 on the pivot of the pointer. It moves freely. Reassembled. The shadow appears a bit wider now, but no cigar. It still doesn't move when going on and off stations.
I'm attaching a photo of the unit inside. I placed red lines on the photo where I rubbed a magnet over the metal. When the magnet was placed at those points the pointer would immediately pull to that area.
Was just wondering. Could that piece be brass instead of metal? Could it be attracting the pointer by a different method? A magnetic field instead of a magnetized piece of metal?
Went to my bone yard and located a model 45-2086 shadowmeter. Mounts the same but has a different type of construction. Looks like a set of small points inside like a car radio vibrator. It's coil read 1.35K. Lubed the pointer/flag with a drop of WD-40 and put it in place on the chassis.
Take a good look at that 2K resistor. I just did some fine tuning on an AK 559. On the AK the resistor appears to be a shunt - but the meter will not function with it open. My meter had become somewhat less sensitive, probably due to loss of polarization of the vein. I was able to increase the movement of the meter by LESTENING the value of the resistor (not intuitive considering the shunt function). Resistor value is now 1.5K and the meter moves through it's range.
Maybe this is too little, too late, but you can always check any of the Philco shadow meters by briefly connecting a 9V battery. That should be enough to make the meter deflect real well. If it deflects you know the meter is good (though the magnet may still be weak). If it doesn't deflect at all, something is wrong with the shadow meter.
I'm not sure that this sm has a fixed magnet. I believe that the spring centers the vane (that's what the magnet does).
It also sets the tension on the vane. I would tighten the adjustment screw on the back till just keeps the vane centered. Any more than that will add resistance to the vane movement which the electromagnet will be fighting against.
GL
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
I wondered what the screw adjustment was for Terry. Now I know. Evidently these two shadowmeters don't have a magnet like other Philcos do. They do have a spring and an adjustment screw. It's interesting to know that the purpose of the magnet or spring is to center the shadow. Thanks for the information.
John
"I see," said the blind man as he picked up his hammer and saw.
As far as I know there are three different models. I know I seem like a know it all but maybe more. Early style has a square box at the back end of the sm. Inside there's a vertically mounted electromagnet. Under it there is a small thin permanent magnet use to center the vane.
Next model has the spring in the center to center the vane and has a smaller horizontal mounted electromagnet. I'd guess that thse were used around 1935-36. These seem to have a lower resistance than the others around 500-900 ohm where the older one are closer to 1.5K
The later models 37 &38 have a round permanent magnet held in by a snap ring and the electromagnet is around a metal tube that supports the vane.
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
