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201X Shadow Meter not deflecting - Printable Version

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201X Shadow Meter not deflecting - Patrick - 05-26-2018

I must be missing something. I can't get the shadow meter to deflect more than approx. 1/32 of an inch.

First of all, the meter seems O.K. The vane moves freely and recenters itself (it's an older style meter). I have tried 2 different 37 tubes, with no change. The voltage on the plate is correct, both 2 meg resistors are new,as is the #66 cap.

The vane is centered on a strong station. But when I go off-frequency, it moves, but just barely. And the padder, #61, has no effect at all. I'm not sure how much the voltage on the plate should vary, but it only changes about 2 vdc.

This is my first experience with a shadow meter, so I'm not that familiar with it, but it seems straight forward.

Anyone with any ideas?

Thanks,

Pat
[Image: http://i1367.photobucket.com/albums/r796/paydirt2/shadow1_zpsgbvcogj0.jpg]

[Image: http://i1367.photobucket.com/albums/r796/paydirt2/201x%20Schematic_zpsn3htltlj.jpg]

RE: 201X Shadow Meter not deflecting - morzh - 05-26-2018

Magnet?

RE: 201X Shadow Meter not deflecting - Patrick - 05-26-2018

When I deflect the vane (power off) with a toothpick, it returns quickly to center.

RE: 201X Shadow Meter not deflecting - KCMike - 05-26-2018

Since your vane is moving smoothly this might not help but here is info on the new and old style shadow meters. Like morzh I was thinking possibly weak magnet.
https://web.archive.org/web/20160727192124/http://www.philcorepairbench.com:80/tips/svctip01.htm

RE: 201X Shadow Meter not deflecting - Patrick - 05-26-2018

(05-26-2018, 12:11 PM)Patrick Wrote:  When I deflect the vane (power off) with a toothpick, it returns quickly to center.

(05-26-2018, 12:29 PM)KCMike Wrote:  Since your vane is moving smoothly this might not help but here is info on the new and old style shadow meters. Like morzh I was thinking possibly weak magnet.
https://web.archive.org/web/20160727192124/http://www.philcorepairbench.com:80/tips/svctip01.htm

I had a copy of those tips. Strong magnet, coil not open. But I didn't remove it from the circuit and test it with a variable power supply. I should have done that first. I'll try it now.

RE: 201X Shadow Meter not deflecting - Phlogiston - 05-26-2018

There is adjustment on most shadow meters, Atwater Kent, Zenith, but Philco is a bit different. On the others, the coil can slide front and back and also rotate slightly. These adjustments are made to make the meter more sensitive. I don't remember if any of this applies to a Philco, but you might look.

RE: 201X Shadow Meter not deflecting - Patrick - 05-26-2018

(05-26-2018, 03:52 PM)Phlogiston Wrote:  There is adjustment on most shadow meters, Atwater Kent, Zenith, but Philco is a bit different. On the others, the coil can slide front and back and also rotate slightly. These adjustments are made to make the meter more sensitive. I don't remember if any of this applies to a Philco, but you might look.

Thanks. I'll take a look.

RE: 201X Shadow Meter not deflecting - Radioroslyn - 05-27-2018

Something else you could try is adding a few volts + to the grid of the 37. This would cause the plate to conduct the max current (abt 8ma) thru the tube and deflect the vane. Conversely you could add some - voltage which cause the sm to act as if there's a very strong signal. Would think something around 10vdc or less.

GL