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Joined: Apr 2019
City: Rochester
State, Province, Country: NY
I have a c-1608 that I am attempting to bring to life. I so far have replaced the paper caps with film caps, and installed a positive ground solid state vibrator. This brought the speaker circuitry to life, am getting about +175 volts on the B+. I can get noise from the speaker now, by touching a probe (or anything) to the volume control center tab. It could't do this before.
However, the second IF transformer measures open on both primary and secondary, as well as the coils having a quite evident black color. This IF is 470 kc. Any idea where I might be able to find this part or an equivalent? I haven't found any. Any other suggestions?
Posts: 7,213
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Joined: Dec 2009
City: Roslyn Pa
Hi and welcome,
On the 2nd if transformer the secondary will be difficult to measure the resistance as it has two internal caps and a resistor connected to it. Short of measuring it at the winding you won't get an accurate reading. With the transformer connected how much voltage do you have @ pin 2 of the 78 if amp tube?
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: 2
Threads: 1
Joined: Apr 2019
City: Rochester
State, Province, Country: NY
Just got the radio back together. I'm measuring 0 volts @ pin 2 of the 78 tube.
Posts: 7,213
Threads: 266
Joined: Dec 2009
City: Roslyn Pa
Well that's not good. A lot of the '37 and '38 models use the 470kc IF transformers. Probably not a lot of difference electrically in the IF output transformers barring the '116, 690, and farm sets. Physically don't know what would be a good fit. You may be able to fit the replacement innards into the original can.
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: 136
Threads: 27
Joined: Dec 2016
City: portland, OR
you can test the audio circuit by touching the tip of a soldering iron to the metal cap on the 75 tube. just plug the soldering iron in, don't turn it on. if the audio part of the circuit is working, you'll hear a 60 cycle hum thru the speaker.
you should have about 200 V [DC] at pin 2 of the 78 tube. that's the plate. and the voltage comes thru the IF coil. if you're getting 0 volts, the coil is probably open. but check the voltage coming out of the rectifier [pin 4 of the 84 tube]. it too should be about 200V. and has to be if you're getting sound.
I've found open coils on the RF and IF transformers in similar philco radios out of fords. seems they have a history of corroding. mine had turned green where the wire had corroded away. if you can tune a station that is a multiple of 460 kHz, you likely have a bad IF coil. frequencies 920 and 1380 are harmonic to 460 kHz and generate the IF themselves. see ron's post/thread about the Philco 89 from H**l for other tips.
https://philcoradio.com/phorum/showthread.php?tid=6
the IF coils in the ford radios have one coil wound on top of the other. I was able to replace the outer coil which only had 20 or 25 turns as I recall.
(This post was last modified: 07-16-2019, 09:27 PM by
fenbach.)
