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Shadow meter questions - Printable Version

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Shadow meter questions - mwoodruff - 02-21-2019

1.  What the Dickens is it?

2.  Is there a way to test it?

I detached it from my 16B; looks pretty beat up.  Wanted to know if there is a way to see if is working now--or do I have to get the rest of the set working first (sometime about 2028 ...)

Thanks.

Matthew W. Woodruff

RE: Shadow meter questions - Radioroslyn - 02-21-2019

>What the Dickens is it?

It's a coil that causes a small vane off center when there is current flow thru the coil. There also the a permanent magnet used to center the vane and a lamp to cast a shadow as the vane moves off center. It a little like a meter movement.
 
> Is there a way to test it?

Yes there are at least two thing to test. Coil resistance should but less than 1400 ohms. The other is the vane blow on it gently should move freely.

RE: Shadow meter questions - klondike98 - 02-21-2019

Here is a helpful link from Chuck Schwark's site
https://www.philcorepairbench.com/shadow-meter-repair-adjustments/

RE: Shadow meter questions - morzh - 02-21-2019

To add to Terry's:

The third thing is, connect 10V across the coil and the vane should move. If it doesn't and the coil is good and the vane is not impeded, the magnet then is de-magnetized.

The whole thing is a crude cheap version of the same thing we have in analog meters.

RE: Shadow meter questions - Radioroslyn - 02-21-2019

> the magnet then is de-magnetized.

I'm kinda up in the air about what the pm does. Thinking that it's purpose is the keep the vane centered when there is very little current flowing thru the coil. I don't think my 116B has a magnet, it has a small spring and an adjustment screw to center and set the sensitivity.

RE: Shadow meter questions - morzh - 02-21-2019

Terry

Yes, I think it is there to keep it centered. But many complain about the thing not functioning when the magnet is dead.

RE: Shadow meter questions - Stall-U-Rated - 02-21-2019

With my 16b, i desoldered the wires from chassis  (note polarity) and used a 9 volt battery. I got swing both ways as i reversed the battery terminals.  After i recapped the chassis, i hooked it back up and it is closed till the tubes warm up and the shadow widens..

A station or two will narrow the shadow gap slightly, but not much action ive seen elsewhere on the dial.. I havent tuned up the radio as of yet to see if the action will improve...

By the looks of the petrified black cloth tape on the SM wires, im gonna guess mine was either fixed or replaced somewhere in the radios life..

Steve