03-19-2018, 11:41 AM
Hi Greg,
>I measure 3.1 ohms on the secondary. What should the primary measure?
Don't know and it's not particularly critical as long as it's not 100's or 1000's or ohms.
>I've read anything from 14 turns and 25 turns of 36 to 40 ga wire. Before I start unwinding...and lose count...does anyone know which it should be?
Good question. I think I've read that the wire ga is 38 but again it's not particularly critical. The direction IS. As for the # of turns if you don't have enough the oscillator won't oscillator at the low end of the band. If you have too many it's tends to distort the output of the oscillator. There is a couple of ways to measure the original. You can measure the width of the coil and wind it's replacement to match it's width using 38ga wire. You can clean off some of the wax and use a pin dragging it over the turn and count to bumps/turns. Or you can unwind it although it can be a little tricky as the turns sometimes just fall apart from rot.
>I had an extra OSC coil from a model 89 that I rewound years ago and I tried it on this model 84. I was able to get the local (strong) station in at full volume faintly. It does get a bit louder when I touch the antenna wire I have connected (but not as loud as it should).
It could be a tracking issue as the osc (460kc higher than the incoming signal) and ant circuit (at the incoming signal's frequency) must be tuned to the proper frequencies for the set to have good sensitivity. It must do this across the whole band. By touching the ant wire it's telling me your ant is too short.
>That coil measures 6 ohms on the primary and 5 ohms on the secondary.
Doesn't mean a thing other than the coils aren't open. Resistance varies w/the length and ga of the wire. It's all about the inductance. Generally in an oscillator circuit the feedback winding is going the be about 20% of the # of turns that are on the tuned circuit. So if the tuned circuit (secondary in your case) is 80 turns your feedback winding (primary) is going to be about 16 turns.
>I then tried one of those AES replacement OSC coils and couldn't get a single station to come through with it.
Well there are a lot of factors in play. Mostly was it oscillating? And if it was was it anywhere near the frequency it needed to be (460kc above the incoming signal). The good thing about it is that the AES coil does have a slug adjustment so you can set it to track properly. I've never bother to try using one in a Philco set as it's easier and quicker just to rewind the old one.
>Could the low volume be caused by too much resistance on the model 89 coil? The secondary on the model 89 coil has a lot more windings than on the model 84 coil.
No the resistance doesn't matter. I would suspect that it wasn't oscillating and that your local station is strong enough to bypass the mixer and get to the detector stage.
>I measure 180 ohms from the antenna clip to GND with the volume control all the way open (and the set off). I *think* the ANT coil primary is good based on that?
Hmmm Seems a little suspect. Would think that it should be lower in resistance. If you do the math, we know the resistance of the 38G wire is .66 ohms per foot. This = about 273' of wire @ 180 ohms around a 1'' dia form. I think this works out to about 1043 turns although my math skills are not very good. I'd pull it out and look for green spots but I'll bet it's no good or there's a volume control issue.
Just as a quick example 38G wire is .66 ohms per ft. Just two sizes smaller (40G) is 1.0 ohms per foot, almost twice as much. I rewound a shadow meter coil w/40g, the total resistance was a little over1500 ohms. That 1500' of wire on a 1" x 3/8" form!
>I measure 3.1 ohms on the secondary. What should the primary measure?
Don't know and it's not particularly critical as long as it's not 100's or 1000's or ohms.
>I've read anything from 14 turns and 25 turns of 36 to 40 ga wire. Before I start unwinding...and lose count...does anyone know which it should be?
Good question. I think I've read that the wire ga is 38 but again it's not particularly critical. The direction IS. As for the # of turns if you don't have enough the oscillator won't oscillator at the low end of the band. If you have too many it's tends to distort the output of the oscillator. There is a couple of ways to measure the original. You can measure the width of the coil and wind it's replacement to match it's width using 38ga wire. You can clean off some of the wax and use a pin dragging it over the turn and count to bumps/turns. Or you can unwind it although it can be a little tricky as the turns sometimes just fall apart from rot.
>I had an extra OSC coil from a model 89 that I rewound years ago and I tried it on this model 84. I was able to get the local (strong) station in at full volume faintly. It does get a bit louder when I touch the antenna wire I have connected (but not as loud as it should).
It could be a tracking issue as the osc (460kc higher than the incoming signal) and ant circuit (at the incoming signal's frequency) must be tuned to the proper frequencies for the set to have good sensitivity. It must do this across the whole band. By touching the ant wire it's telling me your ant is too short.
>That coil measures 6 ohms on the primary and 5 ohms on the secondary.
Doesn't mean a thing other than the coils aren't open. Resistance varies w/the length and ga of the wire. It's all about the inductance. Generally in an oscillator circuit the feedback winding is going the be about 20% of the # of turns that are on the tuned circuit. So if the tuned circuit (secondary in your case) is 80 turns your feedback winding (primary) is going to be about 16 turns.
>I then tried one of those AES replacement OSC coils and couldn't get a single station to come through with it.
Well there are a lot of factors in play. Mostly was it oscillating? And if it was was it anywhere near the frequency it needed to be (460kc above the incoming signal). The good thing about it is that the AES coil does have a slug adjustment so you can set it to track properly. I've never bother to try using one in a Philco set as it's easier and quicker just to rewind the old one.
>Could the low volume be caused by too much resistance on the model 89 coil? The secondary on the model 89 coil has a lot more windings than on the model 84 coil.
No the resistance doesn't matter. I would suspect that it wasn't oscillating and that your local station is strong enough to bypass the mixer and get to the detector stage.
>I measure 180 ohms from the antenna clip to GND with the volume control all the way open (and the set off). I *think* the ANT coil primary is good based on that?
Hmmm Seems a little suspect. Would think that it should be lower in resistance. If you do the math, we know the resistance of the 38G wire is .66 ohms per foot. This = about 273' of wire @ 180 ohms around a 1'' dia form. I think this works out to about 1043 turns although my math skills are not very good. I'd pull it out and look for green spots but I'll bet it's no good or there's a volume control issue.
Just as a quick example 38G wire is .66 ohms per ft. Just two sizes smaller (40G) is 1.0 ohms per foot, almost twice as much. I rewound a shadow meter coil w/40g, the total resistance was a little over1500 ohms. That 1500' of wire on a 1" x 3/8" form!
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
