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Philco Model 91 shadowmeter - Printable Version

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+--- Thread: Philco Model 91 shadowmeter (/showthread.php?tid=1491)


Philco Model 91 shadowmeter - Dave Slusarczyk - 11-12-2008

Evening guys,

Just finished rewinding the shadowmeter on my model 91 and was curious as to the resistance measurement. I used 40 gauge wire and have 475 ohms. Does this seem about right??

Second question if I may. It appears my model 91 is slightly different then what is posted on Nostalgia and what is in my riders. Someone had written "51 series" on the tube chart on the shield.

The biggest difference is it appears my shadowmeter is tapped from the B+ prior to the choke and then to resistor 14 then to the meter. I would think it preferable to be tapped in after the choke.

Either way it seems like a LOT to ask of 40 gauge wire to handle B+ voltage!

Any thoughts?

Thanks,
Dave

Re: Philco Model 91 shadowmeter - Ron Ramirez - 11-13-2008

Hi Dave

Here is another thread on this subject.
http://philcoradio.com/phorum/showthread.php?tid=1455

According to Alan Douglas, the resistance he came up with on a shadowmeter he rewound was 1760 ohms.

As to your second question, a Model 51 (51 series) is quite different from a Model 91...maybe they meant "14 series"?

Re: Philco Model 91 shadowmeter - Dave Slusarczyk - 11-13-2008

Thanks Ron,

I am at a loss as to the resistance measurement. I beleived it to be 40 gauge wire which I unspooled. I will double check.

I just have difficulty running the B+ through 40 gauge wire--or smaller. Seems as if one is torture testing the wire. Perhaps this is the reason I have seen a couple of sets with bad shadow meters-----

Thanks again Ron for the quick reply!!!

Dave

Re: Philco Model 91 shadowmeter - etech - 11-13-2008

Hi Dave,

The shadow meters I have here that are working are from the 650B and 116B models. They are measuring between 1100 and 1200 ohms as supplied by Philco. I don't know what readings would be normal for the shadow meter on the model 91. Icon_smile

Ed

Re: Philco Model 91 shadowmeter - Dave Slusarczyk - 11-13-2008

Thanks Ed,

Someone had bypassed the open coil in the shadowmeter years ago. They had used an 1100 ohm resistor. I am going to assume that with your help and Rons plus the resistor in the set that I will need to shoot for the 1100 ohm range. I did study the wire I pulled off the coil again under a lighted magnifying glass and it now appears to be smaller than 40 gauge. The smallest I have is 44 gauge. I will try it tomorrow evening and see what measurement I end up with.

Thnaks guys!!
Dave

Re: Philco Model 91 shadowmeter - etech - 11-13-2008

Hi Dave,

I am interested in what you are using to wind the shadow meter coils. Do you have a professional coil winding machine? I am using a home brew winder made out of a variable speed cordless drill motor. I have constructed a crude foot control out of the trigger switch. Here is a picture of mine.

Coil Winder
[Image: http://i135.photobucket.com/albums/q136/etech_photos/CoilWinder1.jpg]

Foot Switch
[Image: http://i135.photobucket.com/albums/q136/etech_photos/FootSwitch.jpg]

Ed