Posts: 26
Threads: 6
Joined: Jan 2011
City: Bothell, WA
Hello, I'm new to this forum. I'm also somewhat new to radio restoration.
I just finished recapping a Philco 16b, and it plays like a champ. Good volume, good tone, sensitivity is good on stations. The problem I have is that the shadowmeter doesn't react to the stations. I followed the steps on the repair bench by pulling out the 80 tube and seeing what the meter looks like, and it is perfectly aligned. All you can see is a narrow band. When I turn it on, the shadow expands to where it covers about 3/4 inch. I can tune in stations, but it doesn't seem to react. I have 220v going to the meter. Measuring across the meter I show -8.9v untuned and -6.6v tuned
Any thoughts on where I should begin looking? I'm kind of stumped.
I appreciate any help you can give me.
Thanks,
Chris
Posts: 151
Threads: 5
Joined: Oct 2005
City: Sullivan, MO
Hi Chris,
Welcome to the Phorum. Which version of the 16 chassis do you have? If it is the code 125 or 126 chassis you might check the value of the 5000-ohm shunt resistor that is wired in parallel with the shadow meter coil. There was also a revision on these codes to change the value of this resistor to 2500-ohms.
Sean
WØKPX
Posts: 26
Threads: 6
Joined: Jan 2011
City: Bothell, WA
If I understand it correctly, it's the code 121.
CHris
Posts: 7,285
Threads: 268
Joined: Dec 2009
City: Roslyn Pa
Hi and Welcome!
I'd pull off one side of the shunt resistor(the one across the shadowgraph) and measure the resistance of the coil. It may be open.Not sure about the exact resistance but would guess about 1,000ohms maybe a bit higher. I hope not 'cause it pain to rewind. Take a look here:
http://www.philcorepairbench.com/tips/svctip01a.htm
Hope this helps
Terry
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When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
Posts: 26
Threads: 6
Joined: Jan 2011
City: Bothell, WA
On the 16b that I have (code 121) there is no shunt resistor. The coil reads 901 ohms.
Chris
Posts: 26
Threads: 6
Joined: Jan 2011
City: Bothell, WA
I did some reading on the service tips, and one thing it talked about was realignment if the shadow meter is not responsive. I don't have the equipment to do one properly, but I tuned into a strong station at 1400k and adjusted the IF cans. Very, very little adjustment. The shadow meter responsiveness improved. I also did this at about 530k. The tuned voltage is now about 4.2v and the untuned voltage is about 9.0 volts.
Chris
Posts: 7,285
Threads: 268
Joined: Dec 2009
City: Roslyn Pa
Glad to hear you got it figured out. Sounds like your set wasn't developing enough avc voltage to cause enough fluctuation. in the plate current in the rf amp tube. Next step would be to get hold of a signal generator to do the IF alignment. This will get your avc voltage up to it's highest potential and give you the best selectivity.
Terry
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
Posts: 26
Threads: 6
Joined: Jan 2011
City: Bothell, WA
Terry, I appreciate all your help here. I did swap the rf amp tube for another, and it played the same. I'm sure it just needs to be aligned. That will have to come another day. I'm still learning!
Thanks again,
Chris
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