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Shadowmeter Questions - Printable Version

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Shadowmeter Questions - Jamie - 10-03-2013

I've finished the chassis on my 37-650 and I'm trying to fine tune my shadowmeter. It is the later style. The meter is working and the vane is moving freely, however, the coil is difficult to move. I can rotate it about 20 degrees, and it does move forward and back, but it's sorta stuck, so when I try to adjust it, it jumps from one extreme to the other.

Would it be okay to spray some wd-40 on it to lubricate it?

Also, there is a metal disc in the rear of the meter housing that is a bit loose. I believe it is the magnet. If I move the coil forward, the disc slips out of the rear. I can press it back in place and it stays, but any vibration will cause it to slip.

Should I try to glue it in place, or leave it be?

I don't have much experience with shadowmeters, so I don't know what is considered normal.

RE: Shadowmeter Questions - Jamie - 10-03-2013

   

I installed the chassis, then adjusted the shadowmeter as best as I could. The metal disc that is loose is for sure the magnet. When it drops out of the housing, the meter stops working. When I push it back in, it springs to life again.

This photo is the meter dialed to my home transmitter. Signal strength is medium, some local stations are stronger. I have a six inch wire connected for an antenna.

Should the shadow be narrower?
Should I glue the magnet in place?

I don't know much about shadowmeters and I feel like I've done ok just to get this far.

RE: Shadowmeter Questions - KCMike - 10-03-2013

PuhPow, Did you check the Philco repair bench site/ hints and tips? I was just reading about the shadow meter there and its good info. on how they work and how to adjust them. I whis I could answer yous question but I'am still trying to learn myself.

RE: Shadowmeter Questions - Jamie - 10-03-2013

..

Thanks Mike...

I sure did check out that site. That's how I got this far. Without that site, the shadowmeter wouldn't even be working. Chuck's site is a lifesaver.

One weird thing.. The radio has been playing for 4 hours now and it seems like the meter is somehow getting stronger. The shadow is narrower and it's responding a lot quicker now.

RE: Shadowmeter Questions - Chuck Schwark - 10-03-2013

Remember, the shadow meter responds to RF and IF tube plate current fluctuations due to being tuned on-staion and off station signal strengths. The better the set is aligned, the greater the AVC voltage that influences the grid bias on those tubes and subsequently the plate current draw on the B+ line through the shadow meter (in the B+ line). Depending on the strength of the bias magnet in the about all you can ask of a 60-70 year old permanent ring (C-shaped) magnet in the shadow meter.

DO NOT EVER SPRAY WD-40 IN THERE. Maybe a teeny-tiny drop of watch oil - very light type at the pivot points.
Usually you don't have to lube at all, unless there was corrosion at the pivot points and subsequenly cleaned. If the pivot holes are good,
I woul not lube at all, if it's freely moving with a puff of air.

Chuck

RE: Shadowmeter Questions - Jamie - 10-04-2013

Chuck,
I think there is a misunderstanding here. The vane is not stuck. It moves freely. The coil is stuck. I can move it, but it's very difficult. It jumps from one extreme to the other, making fine adjustment very difficult. I was asking about using WD-40 to free up the coil. Would this be ok? If not, what is the proper procedure for a stuck coil?

Also, the magnet is loose. It falls out of the back of the coil very easily. Right now, it is just pressed in there, but it will fall out again if the radio is moved. Would it be ok to add a drop of glue to the magnet?

The meter is actually working well now. Yesterday, I listened to it for several hours...As night set in and signal strength increased, the shadow narrowed considerably. Thank you for having a great site. Without the info on your site, my meter would not be working at all.

RE: Shadowmeter Questions - marty - 10-04-2013

Hi All;
PuhPow, I have never had a ShadowMeter, but maybe Your problem is not the Coil, but a weak Magnet.. I have watched a number of video's on ShadowMeters and just thought that it might be something for You to look at.. Google "Youtube ShadowMeter" and see what you get..
THANK YOU Marty

RE: Shadowmeter Questions - Chuck Schwark - 10-04-2013

Ah..sorry, misunderstood. Yes, rotating the coil is the adjustment.

I would be very careful and use a small drop (with a toothpick) of Liquid Wrench, PB Blaster or other rust busting solvent and let it sit for at least 5 mins to work its magic.

Chuck

RE: Shadowmeter Questions - Tom Hamilton - 10-07-2013

On You Tube there are a couple of videos done by Joernone on the earlier version of the shadow meter. This meter was used on his Philco 630B repair and restoration video. It took a couple of videos to solve his problems. Part 27 and 28. http://www.youtube.com/watch?v=5nc2dLf6a0s. He was having some magnet problems and was able to make the magnet stronger.

Good luck with yours.

Tom

RE: Shadowmeter Questions - Jamie - 10-07-2013

Thanks guys. I think I have it licked now. It's working great. Marty, I did use one of those things mechanics use to grab dropped bolts (has a magnet on the end), to strengthen the magnet in my meter. I did that early on. Works like a charm. Tom, my meter is the later style and has an adjustable coil, but thanks for the link to the videos. I'll save that for the time in the future when I get a Philco with an older meter.

it is really cool to have a working shadowmeter and I bet it was a big selling point for Philco back in the day.