04-05-2014, 10:00 AM
Hi Winston,
I'm fairly new to this forum as well, but I've managed to restore several radios so far and happen to be working on a Philco 60 right at the moment. If you have any questions about what the chassis should look like I'm happy to send pics. I'll be staring at one for most of today.
A few suggestions. It's great that you have a signal generator-- that can be really helpful in diagnosing problems. For safety reasons, I always put a capacitor in series with my tester. Not so much to protect me, but to protect the signal generator from stray high DC voltages. Also, always use your isolation transformer. Lots of high voltage lines under the chassis, and you need to be very careful and use every safety precaution.
If you are serious about radios, take the time to read Elements of Radio Repair. There is a scanned copy in the Antique Radio Forum archives at http://www.antiqueradios.com/archive.shtml. I think it's worth investing the time in reading it, and it will teach you how to troubleshoot your radio using your signal generator.
The basic idea is to start at the speaker and work backwards through the set. At each stage, you feed in the appropriate signal (audio, modulated IF or modulated RF) and see if you get any sound at the speaker. As you work through it systematically, you will eventually find the problem.
Here's a quick sketch:
1. Start with the power supply. Make sure all the tubes light, and check the output voltages with your meter. If these aren't correct, nothing is going to work. If your tubes light, they probably work. If you have access to a tube tester, check each of them.
2. You should have some audio output from your signal generator. Put this across the speaker coil and see if you hear a tone. If you do, the voice coil and field coil are working. Otherwise check them out closely. You set should be on in order to energize the field coil when you do this.
3. Similar to #2, use the audio output to check the audio output transformer. You can do this by feeding audio to the plate of the 42 tube (for tubes circuits, almost always the plate is the output and the control grid is the input). If this doesn't work, check out the transformer. It's located on the speaker.
4. Next, try feeding and audio signal into the 42 tube at the control grid. Looking at a schematic, the control grid is placed next to the cathode. For the 42, this is pin 4. You can find pinouts of all your tubes on the internet. If this fails, check both the 42 tube and the voltages at each pin. There could be a tube failure or a problem with the bias voltages.
5. Set your signal generator to 460 kHz with internal modulation. Now you have some audio signal riding on the IF frequency. Try feeding this in at the plate of the 78 tube and after the 2nd IF transformer. If it fails, you know which general area to look in. You can also feed some IF in at the plate of the 6A7 and after the 1st If transformer. See what does and doesn't work.
6. Last check is feeding RF frequencies in at the antenna, and then seeing if you can tune them in with the tuner capacitors.
As long as you keep trying, you will eventually figure it out. If the above steps don't seem to make sense, spend some time reading Elements of Radio Repair. It does a nice job of explaining exactly how these old sets work and how you can fix them.
You should also see if there is an antique radio club in your area. We have a wonderful group here in Saint Louis, and I have learned an enormous amount from the people in our club.
Good luck and hope this helps!
Roger
I'm fairly new to this forum as well, but I've managed to restore several radios so far and happen to be working on a Philco 60 right at the moment. If you have any questions about what the chassis should look like I'm happy to send pics. I'll be staring at one for most of today.
A few suggestions. It's great that you have a signal generator-- that can be really helpful in diagnosing problems. For safety reasons, I always put a capacitor in series with my tester. Not so much to protect me, but to protect the signal generator from stray high DC voltages. Also, always use your isolation transformer. Lots of high voltage lines under the chassis, and you need to be very careful and use every safety precaution.
If you are serious about radios, take the time to read Elements of Radio Repair. There is a scanned copy in the Antique Radio Forum archives at http://www.antiqueradios.com/archive.shtml. I think it's worth investing the time in reading it, and it will teach you how to troubleshoot your radio using your signal generator.
The basic idea is to start at the speaker and work backwards through the set. At each stage, you feed in the appropriate signal (audio, modulated IF or modulated RF) and see if you get any sound at the speaker. As you work through it systematically, you will eventually find the problem.
Here's a quick sketch:
1. Start with the power supply. Make sure all the tubes light, and check the output voltages with your meter. If these aren't correct, nothing is going to work. If your tubes light, they probably work. If you have access to a tube tester, check each of them.
2. You should have some audio output from your signal generator. Put this across the speaker coil and see if you hear a tone. If you do, the voice coil and field coil are working. Otherwise check them out closely. You set should be on in order to energize the field coil when you do this.
3. Similar to #2, use the audio output to check the audio output transformer. You can do this by feeding audio to the plate of the 42 tube (for tubes circuits, almost always the plate is the output and the control grid is the input). If this doesn't work, check out the transformer. It's located on the speaker.
4. Next, try feeding and audio signal into the 42 tube at the control grid. Looking at a schematic, the control grid is placed next to the cathode. For the 42, this is pin 4. You can find pinouts of all your tubes on the internet. If this fails, check both the 42 tube and the voltages at each pin. There could be a tube failure or a problem with the bias voltages.
5. Set your signal generator to 460 kHz with internal modulation. Now you have some audio signal riding on the IF frequency. Try feeding this in at the plate of the 78 tube and after the 2nd IF transformer. If it fails, you know which general area to look in. You can also feed some IF in at the plate of the 6A7 and after the 1st If transformer. See what does and doesn't work.
6. Last check is feeding RF frequencies in at the antenna, and then seeing if you can tune them in with the tuner capacitors.
As long as you keep trying, you will eventually figure it out. If the above steps don't seem to make sense, spend some time reading Elements of Radio Repair. It does a nice job of explaining exactly how these old sets work and how you can fix them.
You should also see if there is an antique radio club in your area. We have a wonderful group here in Saint Louis, and I have learned an enormous amount from the people in our club.
Good luck and hope this helps!
Roger
