The PHILCO Phorum
Model 118 shadowmeter - Printable Version

+- The PHILCO Phorum (https://philcoradio.com/phorum)
+-- Forum: Philco Radio Discussions (https://philcoradio.com/phorum/forumdisplay.php?fid=5)
+--- Forum: Philco Electronic Restoration (https://philcoradio.com/phorum/forumdisplay.php?fid=8)
+--- Thread: Model 118 shadowmeter (/showthread.php?tid=8914)


Model 118 shadowmeter - Steve D - 02-28-2014

I have just finished rebuilding my 118 using my original chassis and a donor parts chassis. The chassis was really butchered and had a lot of the cloth wires chewed by a rodent. I found a few errors in the schematic from Nostalgia Air, markup attached.

All I have left is to rebuild the shadowmeter. I have two shadowmeters to build one good one and have a few questions. Both are in good shape mechanically and both coils read on my ohmmeter. However one coil reads 1.4K and the other 850 ohms. From the info on the Philco repair bench the coil has 1000 feet of 40AWG which works out to about 1K resistance. I am not sure if one coil has shorted turns or the other has connection corrosion. What is the nominal resistance reading spec?

Also the schematic shows a shunt resistor, item 76, a 2.9K resistor. I cannot find item 76 on the parts location. Was it added later or perhaps it is built in to the shadowmeter. This might explain the impedance difference between meters if one has it built in and the other doesn't. I guess I should open both meters up to see.

Thanks,

Steve D

RE: Model 118 shadowmeter - morzh - 02-28-2014

>>a lot of the cloth wires chewed by a rodent.

Just say it the way you thought of it when you saw it first - " chewed by a f... rat! " Icon_lol

RE: Model 118 shadowmeter - jerryhawthorne - 02-28-2014

Steve, I'm not certain when Philco started adding the shunt resistor (external to display) but I have done radios with and without. It was added I suspect when engineers started realizing if the shadow meter coil opened the radio would die completely. The shunt would allow it to continue to operate. Not certain if they made a change in resistance of the coil when they added the shunt.
Jerry

RE: Model 118 shadowmeter - hsusmann - 02-28-2014

For what it's worth my 118 shadow meter resistance is 1180 ohms
and there is a shunt resistor also (not included in the 1180 ohm measurement). I forget what the shunt value is but it's in the ballpark
of what you quoted in your message.

Herb S.
Ithaca NY

RE: Model 118 shadowmeter - Steve D - 03-02-2014

Well I just ran the shadowmeters from a LV supply and both do function properly. After bending the light source to get the shadow centered it takes 10mA for full deflection on the meter with the 850 ohm coil and 15mA for the one with the 1.4K coil. The 850 ohm unit was the one in my original chassis so I will use that one.

I also noticed quite a few differences between my chassis and the donor chassis including the tuner dial and band selector switch. I guess these were running changes. Seems odd that they changed the sensitivity of the shadowmeter by 50% and it is used in the same circuit.

Thanks,

Steve D