The PHILCO Phorum

My Philco 38-12 had an open oscillator coil from pin 1 to 2. From 3 to 4 it read 2.4 ohms on my multimeter.

I decided to try re-winding the 1-2 section. After doing so I have a reading of 3.0 ohms between pins 1-2. 3-4 is essentially unchanged.

I do not know what the ohmage is supposed to be exactly for either section. I can't tell from my schematic or else don't know how to read that. My question is----are these readings close enough??? I understand one section is to make oscillation and one section is for frequency. I don't know which is which.

Anybody help me through this?

I am ready to use jump wires and power it up before re-soldering all the connections (total of 5 wires go to the osc.) in the chassis. Will it work? I am assuming I'll have to adjust the transformers and the padder.

Thanks,
Art

The resistance is not as important a factor as the number of turns. But, if you used the EXACT same size wire then the resistance will indicate if you are in the ballpark. If the wire is off by a gauge the resistance won't be helpful at all.

The 1-2 winding is the more critical of the two. It is the one that determines the frequency. 3-4 is basically a feedback winding similar to a 'tickler' winding and doesn't have much if any effect on the frequency.

I would suspect that the coil is ok unless it has a bad solder connection or corrosion has compromised the copper wire. You can try a hair dryer or freeze spray the see if you can get it to fail.If you think the coil is the problem. You probably don't with to rewind the primary but if you have a burning desire to do so you'll need a 1/2 wood dowel some small wire like 38-42Ga It takes about 120turns wound nice and flat/smooth. After you wind that use some duco cement to glue it in place. Secondary is wound over the primary same size wire about 40t cement too.
Terry

7estatdef Wrote:I would suspect that the coil is ok unless it has a bad solder connection or corrosion has compromised the copper wire. You can try a hair dryer or freeze spray the see if you can get it to fail.If you think the coil is the problem. You probably don't with to rewind the primary but if you have a burning desire to do so you'll need a 1/2 wood dowel some small wire like 38-42Ga It takes about 120turns wound nice and flat/smooth. After you wind that use some duco cement to glue it in place. Secondary is wound over the primary same size wire about 40t cement too.
Terry

*******************************
I'm sure the coil had failed because it was open. The wire I used to rewind is a close as possible to the original wire on the coil.

Well, plug it in and let 'er rip. If it doesn't appear to work DON'T go adjusting anything else just yet. Use the 'second radio' trick to see if you can find the oscillator signal on some oddball frequency. It (the oscillator) may be working but too far off frequency to make the radio play. If you can find the signal then you can determine whether you need more or less turns. If you start tweaking anything else you'll have too many variables in the mix.

exray Wrote:Well, plug it in and let 'er rip. If it doesn't appear to work DON'T go adjusting anything else just yet. Use the 'second radio' trick to see if you can find the oscillator signal on some oddball frequency. It (the oscillator) may be working but too far off frequency to make the radio play. If you can find the signal then you can determine whether you need more or less turns. If you start tweaking anything else you'll have too many variables in the mix.

*********************Not sure what you mean by the second radio trick. Thanks.

AM I MAKING PROGRESS??

Well guys, I rewound the osc. coil on this Philco with 100 turns between #1 and #2 posts. I had to double-layer it---even with about 42 g wire-- to have that many turns.

I jumped the connections--no soldering yet-- and fired it up on my variac, connecting ext. antenna and ground.

I set another good radio next to it and tuned it to 1200 kHz where I heard no broadcast. Then I turned the Philco tuner from one end to the other. I hear nothing except at about 1350-1400 kHz I hear a nice squeal/sqawk. When I turn the Philco off, it stops squealing. When I turn it back on it starts squealing again. I am assuming the osc. is working!? (I hear no motorboating.)

Is it time to start adjusting the i.f.s????? Being a first-timer on this thing, I don't quite know what to expect.

Thanks for your help.

Sounds like it's working! Was the set working for a bit after you replaced the caps? Just to find out where your at, set the 38-12 dial at 550kc.Listen with a set with good calibration place the ant wire near the 6A7 tube it should be heard at 1020kc. If you here it higher in frequency you need to add some more turns. Lower remove a few.
Terry

Okay. No, it was not working before I replaced caps/resistors. Just had a litle motorboating then.
Thanks.

Art Hoch Wrote:Is it time to start adjusting the i.f.s????? Being a first-timer on this thing, I don't quite know what to expect.

Thanks for your help.

No, no, no. Ok, Art. You got it working . That's the first step. DO NOT go messing with the IFs, puleeze! because all of this advice will turn to mush. They have nothing to do with this repair. I know you from many years of posts so I know you must have some savvy.

You can do this by ear if you work at it The "second radio trick" is a technique to find the local oscillator frequency. You should find about 455kc difference between your dial setting and what you hear on the second radio. if you're 100kc off then maybe you'll hear some strong local stations on the wrong part of the dial but at least you have something to work with. 7estaf says the right thing if you are too high or too low. Might have to add/subtract a few turns to get the coil into the infield instead of the ballpark.

Modern frequency counters, an AADE L/C meter or even an old timey Grid Dip Oscillator make a relative breeze out of these issues!

Get that local oscillator coil tuned within 5 or 10 kcs as heard on the second radio then you'll be in like Flynn.

Not to confuse the subject but the IF frequency is 470kc on this set. 455 is the standard most sets use except for Philco and Atwater Kent and some others...
Terry

TESTS ATTEMPTED TODAY (MAY 11)

Several of you have suggested these different tests on this non-working Philco radio to see if osc. coil is working. Here is what I tried today and the results;

#1 Set Philco at roughly 1000 kHz and tune a good radio 455 (470 since it is IF on this one) above and below the frequency on Philco. If you hear the squal osc is working.
Results; With Philco set @ 1000, I get a squawl/squeal on good radio at about 1200 kHz and about 610-620 kHz. Not loud but I hear it. I hear no broadcast anywhere.

#2 Set good radio to a clear spot about 1200 kHz and tune the Philco up and down the dial. Faint whistle indicates the radio's osc is working.
Results; I hear nothing today and I hear no broadcast anywhere.

#3 Set Philco @ 550 kHz and place ant wire near 6A7 tube and it should be heard at 1020 kHz.
Results; I hear nothing & I hear no broadcast anywhere.

Other anecdotal notes. A faint station on the good radio gets noticably stronger when I connect ext. antenna to Philco (this was @ about 1300 kHz.) I also hear the static noise on good radio when I connect the Philco ext. antenna.

When I touch ext antenna wire to Philco 6A7 grid cap, I hear static in the Philco speaker and also in the good radio.

Is it possible I rewound the osc coil the wrong direction? Should I try unsoldering the wires and reverse them---#1 post to #2 post and vice versa? Starting to get a little frustrated to say the least.

Thanks for all your good help.
Art

Go head and switch your leads around. Another way you can check it is to measure the dc voltage from grid 1 (closest to the cathode) and the cathode. Use a VTVM or a FET meter with an input impedance of 10meg ohms. With the + on the grid and the - on the cathode if the osc is running you will see some negative voltage like a volt or 2.
Terry

2nd try today:

Wire broke on the "good" original part of the coil---(#1 to #2 post) and I could not rescue it so I took BOTH original coils off and started over. Old #1 to #2 was 82 winds. I replaced it exactly and it tests 1.8 ohms.

#3 to #4 was only 27 winds. I replaced it exactly and it only tests 0.7 ohms. Jumped the connections again and powered up. Nothing.

I reversed the connections to adjust for a different winding direction....same result.

It seems to me that neither coil is long enough although those are the winds I found. As near as I can tell, I used the same wire size. I know 7estatdef suggested a specific # of turns that differ from what I found on this existing coil. Since I don't have success yet, I'm willing to rewind with a higher # of turns if that would be the consensus here in order to get higher readings on the ohms. I'm nowhere close to the ohmage the schematic suggests (2.5 and 3.5 ohms) I'm assuming #1 to #2 is primary. PERHAPS THIS WAS NOT THE ORIGINAL OSC COIL FOR THE RADIO....I DON'T KNOW.

Any different suggestions? Thanks.