[37silverstreak]

Hey everyone,
It seems to be shadowmeter time on here ! I had to completely rebuild the coil on my 91 shadow meter, form and all. I followed the instructions on Chucks site- 1000ft of 40 gauge magnet wire for about 1100 ohms. The vane moves freely and when I applied 9 volts to the coil the vane deflected and snapped back to center when voltage removed, so everything appears good. After rebuilding the chassis and reinstalling the meter, when I turn on the set the shadow appears narrow in the window and then widens as the set warms up which I believe is normal. The problem I am having is the shadow narrows only slightly on a strong station, but not nearly enough. I read that this can be caused by the set being out of alignment, so I did an alignment and the set plays super, lots of stations all over the dial and very loud, but I still don't get much deflection on the meter. does anyone have any input? I don't need the meter to work to enjoy the radio, but with all the work I put into that darn coil it would be nice!!! Thanks!
Kevin

[hsusmann]

I had the same problem on my 37-650 and I fixed it by
sliding the coil forward on the shadow meter body.

This lessens the magnetic field at the vane and brings the
shadow to a narrower shadow when there is no signal
applied to the antenna.

My shadow meter is of the "New Type" so I don't know if
this adjustment can be done on the "Old Type" or not.

Herb S.
Ithaca NY

[Mondial]

The meter operation seems normal if it starts narrow and then widens as the tubes warm up.

The shadowmeter operates by indicating the plate current of the AVC controlled tubes. As the signals get stronger, the negative AVC bias voltage increases which decreases the plate current, causing the shadow to narrow.

If the AVC voltage is too low, there will be little deflection. Can you measure the AVC voltage with a DVM when tuning in a strong station? You should have at least 10 V of AVC voltage with a strong local signal. If you are not getting that much then there will be too little change in plate current to narrow the shadow significantly.

You can measure the AVC voltage by connecting the negative probe of the DVM to chassis and the positive probe to the top of the volume control ( detector output).

[37silverstreak]

Mondial, it looks like the problem is in the AVC circuit. I checked it out like you said and I am only getting a maximum 1 volt reading on a strong station. Meter appears to function normally otherwise. thanks for the tip!
Kevin

[Mondial]

The problem may not be in the AVC circuit itself. Anything that reduces the RF or IF gain of the radio will cause the AVC voltage to be low. Weak tubes, leaky bypass cap or a drifted value resistor first come to mind.

I would check the voltages on the screen grids of the RF converter and IF tubes and see if they are near spec. A gassy tube can also reduce the AVC voltage as grid current can bias the AVC line positive, reducing or cancelling out the negative AVC voltage from the detector.