[Mike25]

Hello everyone. I'm a new guy here. I'm currently restoring a Philco 635 and have this model shadow meter. Mine is not working right either. I'm getting about 4.5 volts across the coil and it does vary a bit with signal strength. I don't see a magnet of any type. Just the adjusting screw.

Does anyone have any further information on this style meter?

Thanks,
Mike25

[Radioroslyn]

Hi Mike and welcome,
For starters the radio chassis needs to be in tip top shape. This means all new paper and electrolytic caps, all resistor within 20% tolerance and a good set of tubes. Align the rf and IF stages. With a chassis w/poor sensitivity it's a waste of time and is very frustrating to try to get the sm to work properly. A good indication is if you receive a strong signal (from a generator or on air) you should be able to develop about -10v on the avc line.
Use the adjustment screw to set the vane straight. Should be able move the vane by gently blowing on it. If not it's probably centered in it's pivots. Align lamp filament for best shadow.
Generally I find that the sm isn't very sensitive. Doesn't react to weak signals very well. I live in an area where there is a lot of strong signals and a lot of noise.

[klondike98]

Welcome to the Phorum!


I moved your posts (which originated in this THREAD LINK) into their own thread so the discussion does not get confused with the Q&A around the 650 shadow meter.  You can also use this thread to ask other questions about your 635 restoration as you proceed.

You can post pictures and that might help folks sort out whether you are missing the magnet or not.  Here's how to post them: http://philcoradio.com/phorum/showthread.php?tid=29

[morzh]

And then there's this link:

http://philcorepairbench.com/tips/svctip01.htm

[Radioroslyn]

And then there's  this link:

http://philcorepairbench.com/tips/svctip01.htm

Currently Chuck doesn't have much on that particular sm.

[morzh]

Not sure...I see what I always saw. Plus it has the link there "How it works".

http://philcorepairbench.com/tips/svctip01a.htm

[Mike25]

Thanks everyone for the replies! I will try to keep this brief, but let me give you an overview of where the radio is now.

I rebuilt the chassis with all new caps (not counting micas). All resistors have been changed with the exception of two dogbones which checked right on specs. The radio powered up fine, had good volume and was sensitive on all bands. All the tubes are good and checked 65% or better. After alignment I checked the voltages and had a problem with plates on the two 78s and 6A7 being high by about 40 volts and SGs on those being low by about 35 volts. Other voltage readings were close to specs with the exception of the cathode on the 78 IF which was 1.8 vs. 2.6 desired. I rechecked all wiring and component values and everything looked good. I was getting about 1.8 volts across the shadow meter at that time.

See schematic here: http://www.nostalgiaair.org/Resources/814/M0013814.htm

One problem here is the schematic (S) shows one value and the parts list (PL) shows a different one for some of the components (R22 S=2.0M, PL=1.0M), (R30 S=2.0M, PL=51K), (R50 S=99K, PL=20K) and (C51 S=.03mF, PL=.15mF). I originally went with the parts list values as that was what was originally in the radio. They made a change to R50 from 99K ohms to 20K ohms. I watched John's video series on his 630 he did a few years ago and on part 35/35 he had a similar problem with the voltage divider. He had found a change where the factory changed R49 to 10K and R50 to 20K. He ended up changing the value on R50 to around 40K to get his voltage back to where they are supposed to go. I think Philco changed the parts and maybe didn't update the voltage table. Not sure, maybe someone could comment on this? Anyway, I changed the values of the divider to R48 to 16K, R49 to 10K and R50 to 120K and now the voltages throughout the set are close to normal. The G2 grid on the 6A7 is about 25 volts low so I may have to play with the values some more. The radio plays very well and is a lot louder. I still need to realign it.

Now to the shadow meter. This is the same type that was discussed in a previous Phorum thread and pictures can be found here:

http://philcoradio.com/phorum/showthread.php?tid=2861

I'm not sure how this works either. I don't see a magnet in it anywhere. The vane has one ferrous rivet on one side that will attract to a magnet. The schematic shows a coil value of 500 ohms and mine ohms out at 598. Right now I'm getting around 4.5 volts on it and it will decrease by about 3.8 to 4.0 volts on stronger stations.

I guess right now I'm trying to figure out what the normal voltage swing should be across it for strong station and no station. Also, I can get it to move around if I put a magnet close to the vane, but it doesn't move otherwise. I guess the coil generates a magnetic field between the two poles on both sides of the vane, but not sure how its supposed to react unless that rivet was supposed to be magnetized. The adjusting screw in the back just bends a brass band toward the poles from the coil which I guess is supposed to change the magnetic field. I haven't been able to find much about this design at all other that the Phorum link above.

Radioroslyn mentioned the AVC voltage. Where would I read that on the radio?

Again, thanks everyone for the help. I enjoy working on these old Philcos and look forward to getting this one up and running. I've restored a Model 60, 66, 40-120 and a 46-1226.

Have a great day!
Mike25

[morzh]

The magnet is really not what acts to deflect the vane, it is rather like the wound spring in Westons ro bring it back to initial place. Without it the vane will still deflect but might bounce and not get back (act as stuck).

[Radioroslyn]

< Where would I read that on the radio? 
At the bottom diode plate of the 75 tube.

OBTW the sm that Audin posted is missing the spring that centers the vane. I should look like this one.
With out the spring you would need a magnet to center the vane like the older models use. The screw
at the back adjusts the vane position when the spring is in place. Without it it does nothing.

[Mike25]

Great!  That picture is worth a thousand words!  I don't have that spring in mine and not sure where it went.  Makes a lot more sense now.  I'll see if I have one small enough to work.

On the 75 tube, would the bottom diode be D2 pin?

Thanks!
Mike25

[Radioroslyn]

Great!  That picture is worth a thousand words!  I don't have that spring in mine and not sure where it went.  Makes a lot more sense now.  I'll see if I have one small enough to work.

On the 75 tube, would the bottom diode be D2 pin?

Thanks!
Mike25

Wasn't trying to be cagey about the diode pin but I couldn't find a tube diagram that was drawn like the one in the schematic. The diode plates where on the right side rather than the left so wasn't sure which diode was which. So it's the one that isn't connected to the IF transformer. Must use a high impedance meter to measure this voltage.

Glad mine had a spring in else these thing would be a great unsolved mystery!!!!! I found it a few months ago when I was working on the 660L. The original one had an open coil so I was scrounging around looking for a replacement. I was a bit puzzled that the coil resistance is much lower than the other styles their about 1.4K. Now that I look at it it may be that it's more efficient. The vane has a small ear that passes pretty close to the coil. Perhaps it doesn't require as much  magnetism because of the close proximity of the vane and since has a spring it doesn't have fight the fixed magnet's magnetism. And of course it's cheaper to make, less time to wind, less copper.

[Mike25]

Thanks Radioroslyn,

You really did solve a great mystery!  That spring looks really fine.  Mine must have rusted away and evaporated  8) .  I'll see what I can come up with and let you know how it goes and I'll also check that voltage with the VTVM.

Mike25.