I have finished the restoration of my Philco 37-670 cathedral and it works and sounds great. But the shadow meter is not working properly. It is the NEWER type with the round coil in back. I have read all of the excellent material found on the Philco Repair Bench, but no amount of pushing, pulling, or turning the coil will widen the shadow more than about 3/8". The coil resistance is about 1500 ohms. With no antenna connected, the voltage across the coil is 14.62. With a good signal that drops to about 5.9 volts and the shadow narrows to about 1/16" (same as if the rectifier tube is
pulled). So it appears that the receiver's AVC is doing its job.
When the shadow narrows only the RIGHT side of the shadow moves - the left side stays still. Is the possible that the coil is turned the wrong way - grossly mis-positioned (photo attached)? Right now, if the coil is pulled back all the way the leads exiting the coil limit rotation to within the gap on the back of the housing.
Is there a magnet inside that may have weakened and needs recharging? It's not obvious to me how to disassemble the unit and take a look. There is an excellent write up on servicing the earlier type meter on Philco Repair Bench, but I have not found anything on servicing the later type. Any suggestions?
(This post was last modified: 05-03-2016, 05:35 PM by davemc.)
If the shadow is not symmetrical, the filament of the bulb may not be aligned with the light aperture on the back. Philco originally used a special bulb with a precisely located filament. If you substitute a normal 44 bulb, the filament may not be located properly with respect to the aperture. The filament should be directly behind the hole on the back of the coil assembly. If it is not, you will experience an asymmetric deflection of the shadow.
You may have to try several bulbs of different brands to find one that works well.
I also decided to give up on ever getting mine to work like it should.. Although I was able to get the shadow centered, no amount of adjustment would get it to move when I thought it should.. Until I did what can only be called a hAlf@** alignment.. It seems to have found new life.. Maybe one of these days I will get around to adjusting it..
Well, the good news is I think I now know the problem. After viewing the photos on the Phorum, it looks to me that the magnet is MISSING! There is a shadow on the front of the coil that looks like perhaps something was there but no longer. Even though it does not appear that the meter has been fooled with or opened. Can someone confirm that this is the case? Of course, if that is true, then I guess I will never have a functioning shadow meter. Again, the symptom is that the shadow will not fill the screen (with no antenna connected), and when the voltage across the coil is varied, only the LEFT side of the shadow moves - the right side does not. The coil is good, the set has been restored and aligned (at least on the first two bands) and the coil voltage varies between 6 and 15 volts.
There is also a chunk of the coil bobbin missing on the back of the coil, exposing the winding. That, at least, appears fixable. I guess my next move (if the missing magnet is confirmed) is a classified ad.
Its hard to tell from that pic,.. That brown ring looks like the magnet to me.. Is that brown ring metallic?? There would be a very noticeable void there if it were missing.. Mine was loose and flopping around, but would never have fallen out.. It would have to break in half.. It looks to me, like you would have to take the thing apart to get the magnet out..
I scraped away part of the brown ring, which was a wax like material. Whatever is under the wax is NOT metallic and a magnet does not attract it. It think it is just a recess in the coil bobbin. The magnet, if it belongs there, would have to have broken in half in order to go missing! Else someone removed it.
I assumed that it should look something like the photo (Shadow Meter Bobbin) in etech's thread on Shadow Meter Coil Rewinding.
I'll post some pix of what I have later tonight.. Unless I am crazy, (and that could be) that should be your magnet.. Still hard to tell from the pic,.. If there is in fact a step, or recess then maybe it is missing.. The magnet almost flushes out with the back of said bobbin..
Stan
(This post was last modified: 04-04-2016, 02:09 PM by Stan the Man.)
The shape of the wax covering (which is VERY thin) appears to be shaped like a horseshoe magnet. If the magnet is there, the wax (thin layer) does indeed make the end of the bobbin flush, so the magnet would have to be recessed in the end of the bobbin and secured with wax. What confuses me is that the magnet, if it is there, does not attract metal (at the ends or center) - even thin strands of steel wool. And a small magnetic screwdriver does not appear to attract the center area where I removed the wax. That area does indeed appear to be metal.
It may be that my magnet has lost ALL its strength, but is there. I'll be looking forward to seeing your photos. It is weird that there is so much information out there for the old style (box shaped) shadow meter, and nothing I could find about the newer type. SURELY someone has had to re-magnetize a magnet, and thus has disassembled, a new style meter! That's the person I would like to connect up with.
Here are a couple of pictures of my shadow meter.. you can see all the wax is gone from my magnet,.. you can also see the dab of hot glue I put on it to hold it in..
Very helpful - thanks! So likely my magnet is there and simply needs to be "recharged". Did you remove your magnet, or was it a previous owner? It also appears that your coil has been rewound. Mine is OK. It appears that to remove the coil I need to straighten the bent over tabs holding the lamp bracket and remove the bracket. The coil and magnet looks like it can then slide off. I suppose I then melt the wax and remove the magnet for recharging. I have seen the recharging procedure on-line. I have several powerful magnets available for stroking my magnet from one end to the other in the same direction, and check attraction using a pin or other small object. IIRC you said your magnet was reattached using a dab of hot glue.
While disassembled, I assume I need to check for proper vane movement.
If you did your repairs yourself, please confirm the procedure outlined above.
My shadow meter looks original to me.. I believe the wax dried out and flaked off.. the taps don't look like anything has been done..
Also my magnet just does attract the blade of a very small screw driver.. I opted to leave it alone , for fear of breaking the taps or the coil.. I would rather have it as is than to have to fix it or worse, find another.. I brought my philco back to playing condition and that's as far as I wanted to go..
Stan
The magnet can be possibly recharged by locating the poles (likely left and right of that notch where there is no wax) and, using a small strong rod magnet rubbing it, each pole with a different end of the rod magnet.
I do not know if the polarity matters, likely yes, so you could try to determine the polarity of the original with a compass, and them magnetize it the way so it would still attract the same pole of the compass.
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 watching some YouTube videos involving restoration of Philco shadow meters. One mentioned being able to see the vane through the BACK of the meter - where the lamp shines through a hole. I had never thought of doing that, and the lamp and its metal cover blocked vision from that side. I was trying to check the vane operation from the OTHER end. Well, I removed the lamp and sure enough the vane was visible. I connected up a variable DC power supply and varied the voltage from zero to 15 volts (the highest voltage drop I had observed in my radio). The vane moved smoothly as the voltage was increased, and returned to the center (and vibrated) when the voltage was cut. So it looked like my coil and magnet were working properly. Except that half of the vane is missing! That of course explains everything that I observed: that only one side of the shadow moved. Since there is no obvious fix for this, I then just reinstalled the meter in the radio and performed the adjustments. So at least the meter is functional and works as the radio is tuned. But only one side of the shadow moves.
One thing I don't understand is how this could possibly happen! There is no evidence that the meter has ever been opened up.
It seems to have found new life.. Maybe one of these days I will get around to adjusting it..
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