First attempt at rewinding an oscillator coil (Phil 38-12) - Printable Version
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Re: First attempt at rewinding an oscillator coil (Phil 38-1 - Steve Davis - 05-12-2011
Art Hoch Wrote:2nd try today:
I reversed the connections to adjust for a different winding direction....same result.
Art, when you say you reversed the connections, did you reverse the connections on both windings? If so, that would not change the relationship between the windings. You would want to reverse the connection on only one winding.
Steve
Re: First attempt at rewinding an oscillator coil (Phil 38-1 - Art Hoch - 05-12-2011
Steve Davis Wrote:*****************************Art Hoch Wrote:2nd try today:
I reversed the connections to adjust for a different winding direction....same result.
Art, when you say you reversed the connections, did you reverse the connections on both windings? If so, that would not change the relationship between the windings. You would want to reverse the connection on only one winding.
Steve
Yes, I reversed both. Does it matter which one? Have to leave it lay for a couple days. Will try again later.
Art
Re: First attempt at rewinding an oscillator coil (Phil 38-1 - Art Hoch - 05-16-2011
May 16
Think I made a little progress today. I re-wound the coil to the specs (ohms) listed in the schematic...I did not pay attention to the # of turns...just the ohm meter. I have 2.4 ohms on the primary (1-2 lugs) and 3.5 ohms on the other (3-4 lugs). That's what the schem says.
When I jumped the connections I had squeal with the Philco tuner set about 1000. A nearby good transistor squealed about 1500 kHz and about 580-600 kHz. I then shut the radio down and soldered the connections; fired up the Philco and the squeals remained. So I think the oscillator is working...isn't it?
The speaker of the Philco has a very slight hum...that's all.
I'd appreciate suggestions what to do next. Do I start adjusting the IF coils or is there something I'm missing still?
Thanks.
Art
Re: First attempt at rewinding an oscillator coil (Phil 38-1 - Radioroslyn - 05-17-2011
>I re-wound the coil to the specs (ohms) listed in the schematic...I did not pay attention >to the # of turns...just the ohm meter. I have 2.4 ohms on the primary (1-2 lugs) and 3.5 >ohms on the other (3-4 lugs). That's what the schem says.
In reality the resistance isn't the important factor. What matters is the inductance. That's what makes up half of the tuned circuit. The inductance and the capacitance. Now if you are very lucky and you just so happen to pick the same gauge wire as the original then you might have a chance at coming close to the proper inductance on the primary. That's the important part. The secondary is a feedback winding that causes the circuit to oscillate. Not so critical. If you look at just the resistance you would think that the secondary is longer than the primary because it has more resistance. But I know that the secondary only needs to be about 20 percent of the primary for the oscillator to run properly. So the secondary must be wound with small gauge wire or the resistance measurements are wrong. Here's a link to one I did awhile back on a 1936 Philco 600.
http://philcoradio.com/phorum/showthread.php?tid=2139
Terry
Re: First attempt at rewinding an oscillator coil (Phil 38-1 - Art Hoch - 05-17-2011
If you look at just the resistance you would think that the secondary is longer than the primary because it has more resistance. But I know that the secondary only needs to be about 20 percent of the primary for the oscillator to run properly. So the secondary must be wound with small gauge wire or the resistance measurements are wrong.
So is the suggestion to remove much of the secondary wire because it's longer than the primary at this point? If so how many turns? I have about 140 turns right now on the secondary. If so, why does the schem have quite a bit higher resistance measure for the secondary over the primary? I know about inductance but there must be a formula or something to calculate that. Sorry I'm not very "electrical." I'm more eclectic.
Re: First attempt at rewinding an oscillator coil (Phil 38-1 - Radioroslyn - 05-17-2011
No no I was just making the point that the resistance doesn't really mean much when you are working with tuned circuits. Other than whether good (showing a low resistance) or bad (open)
140t might be a little too much but once you get it working what will happen is it won't tune up to the top end of the band. Worst case you'll have to remove some turns from the primary. On my model 600 it should tune up to 1800kc but will only go up to 1500kc. I need to remove a few turns from the primary.
Terry