Hello, Working on a Philco 60 where the AM band stops receiving at about 1450 kc. It just goes silent except for slight noise at full volume. I have to tune the radio back to about 1300 kc before it will start again. I have checked for plates touching and found none. I have rewound the troublesome oscillator coil with 18 turns of #40 wire as it was open. The SW band does not work either. Maybe same problem. Other than that the radio plays quite well. Any ideas?
Thank you,
Dan
Add a few more turns to the feedback winding on the osc coil if it's not a shorting rotor.
I don't understand the message. I don't know what the feedback winding is or what a shorting rotor is.
The feedback winding is the section of the oscillator coil that you rewound. Try adding 4 or 5 more turns to the existing. The rotor is the part of the tuning capacitor turns or rotates with plates. The fixed portion at the bottom w/plates is called the stator.
Sometimes the rotor plates can get bent just a little and rub on the stator. This short the tuning cap out of the circuit. Most or the time it's the rotor plates at either end. They have cuts in them alignment/tracking purposes.
Got it. I don't know how I will add turns so I guess I'll just rewind using 5 more turns of my original 18 making 23 turns. I had used #40 wire before and since have seen where others are using #38. Doing 23 turns of #38. I had used double sided tape between the layers is that OK?
Could be that using 40g wire instead of 38 may be the issue in terms of inductance which is what we are shooting for. Have never used double sided tape to isolate winding before, didn't have it back in the day.
I would just cut one end loose and wind the extra turns on. But to each they own.
I have rewound the coil using #38 @ 23 turns. The problem has moved where reception stops at 1250 or so and have to back off to 1150 or so to restore reception. Shortwave still does not work. Any thing else I can try?
Dan
You might try another 6A7 tube
Steve
I tried two others 6A7 tubes. They didn't make any difference that I could tell. Since I went from 18 turns of #40 wire to 23 turns of #38 is that maybe too many turns?
Pull some turns off and see what happens.
I pulled off 3 turns, now down to 20 turns. Stops around 1350 now. So I suppose I keep pulling off turns until I get full scale? I assume that is going to be the 18 turns I had at the start with the #40 wire. Do you think that will bring back the shortwave?
I decided to try another 3 turns off now I'm back to 1450 where it stops. I am at 17 turns now. I now have some shortwave starting around 3.2 mhz to about 3.8 mhz, after that lots of squealing. Nothing below 3mhz. I normally get a fair amount of shortwave about this time of day.
Dan
Let's take a step back, what have you done to this set? Caps replaced? Have you aligned the IF @ 460kc w/a generator?
Dan,
This may not be helpful, and I have nowhere near the experience of the guys on this forum. Attached is a page from Radio Troubleshooters Handbook. Just trying to throw something out there and be helpful since I have received so much help from others.
I remember reading about certain models with finicky oscillators and one thing was mentioned is to remove the osc coil and put it on a baking sheet in a 200 degree oven for about half an hour to dry out the core. Seems that some absorb moisture over the years and that affects the oscillator. Maybe worth a try!
Ron
I have checked for shorted tuning condenser plates, replaced e caps, replace caps in the tar blocks and replaced all out of tolerance resistors. I even replaced that cap in the oscillator coil with a new 110pf silver mica. I have done an alignment using a generator at 460. I got a fair amount of gain on trimmer under the 78 tube. The other three IF trimmers were very touchy but I think I have them aligned. By touchy I mean less than a 1/8 of a turn before loosing the signal. I even took out the antenna coil so I could replace the grid cap wire. That outer winding did not look like the outer winding I have been messing with on the oscillator coil. It is wound with a non enamel wire with cloth cover. Looks about #24 wire or less. I didn't know if that was normal or not as I nothing to compare with. I saw a bandersontv video where he showed both coils and his antenna coil looked pretty much like the oscillator coil. So now I wonder if that winding is the problem. I don't have a picture of that coil but if it would help I will take it out and take a picture.