10-02-2022, 12:03 AM
Hi PercyJD,
Does the JD stand for Juris Doctor?
If so, a Disclaimer that the following information is given as a courtesy, and the user is fully and solely responsible for verifying the suitability of this information for use.
Certainly, the 270CAX should work if the Thordarson specs are correct. It may be cheaper to buy a used transformer from eBay, as the Hammond is not going to be cheap
The circuit in this diagram is very typical of other radios of this vintage. I would say that any transformer out of many of these radios would work as long as the donor radio has a field coil type speaker, has 5 tubes and the rectifier is an 80, 5Y3, 5W4 or 5Y4, but the Field Coil resistance of your radio, at 1600 Ohm is rather high. Most radios of this vintage have field coil resistances of about 000 Ohm to 1200 Ohm. The only variable is whether the transformer has an isolated 5V winding, is for a 5 tube radio and what is the High Voltage secondary output. One from a GE G52 or G56 would work. The tubes are almost the same and the field coil is within 200 Ohm of yours. The goal is to have a B+ reading at the Audio Output transformer of around 250V. The B+ voltage into the speaker field coil is usually 50V - 100V higher
One thing you can try is the "Dim Bulb" test. Place a lamp socket in series with the radio power cord. Place a 60Watt bulb in the socket. REMOVE ALL TUBES!
Carefully power up the radio. If the bulb is dim, continue. If the bulb is bright, or arcing occurs, the transformer is seriously shorted. STOP and SHUT DOWN! Measure across the power transformer high voltage secondary. CAUTION!! High voltage!! risk of dangerous or deadly electric shock! If you have no experience working with high voltage, seek help.
If you have experience with high voltage / high current, perform the above measurement across the HV secondary (to the plate connections of the rectifier. Record the voltage. if within 20% of 500V, the Hammond will do. Measure between each leg of the secondary and the center tap. The voltages should be half the voltage across the 2 legs and be within 10% of each other. If seriously off, your short is there.
Sometimes, a transformer just fails. Other times, there is a cause. A shorted rectifier or shorted capacitors will do this.
In addition to replacing the transformer, replace all paper and electrolytic capacitors and check the rectifier tube. Yours is a 5Y4. a 5Y3 is NOT a direct replacement. The socket has to be rewired.
Add a 1 Amp fast fuse between the radio's power switch and the transformer primary. To prevent a shorted rectifier from burning out a transformer, I usually place 1N4007 silicon diodes in series between each plate pin on the rectifier socket and the transformer HV secondary, with the anode connected to the transformer wire and the cathode connected to the plate pin of the tube socket. do this for both transformer connections to the rectifier plates.
Good luck.
Does the JD stand for Juris Doctor?
If so, a Disclaimer that the following information is given as a courtesy, and the user is fully and solely responsible for verifying the suitability of this information for use.
Certainly, the 270CAX should work if the Thordarson specs are correct. It may be cheaper to buy a used transformer from eBay, as the Hammond is not going to be cheap
The circuit in this diagram is very typical of other radios of this vintage. I would say that any transformer out of many of these radios would work as long as the donor radio has a field coil type speaker, has 5 tubes and the rectifier is an 80, 5Y3, 5W4 or 5Y4, but the Field Coil resistance of your radio, at 1600 Ohm is rather high. Most radios of this vintage have field coil resistances of about 000 Ohm to 1200 Ohm. The only variable is whether the transformer has an isolated 5V winding, is for a 5 tube radio and what is the High Voltage secondary output. One from a GE G52 or G56 would work. The tubes are almost the same and the field coil is within 200 Ohm of yours. The goal is to have a B+ reading at the Audio Output transformer of around 250V. The B+ voltage into the speaker field coil is usually 50V - 100V higher
One thing you can try is the "Dim Bulb" test. Place a lamp socket in series with the radio power cord. Place a 60Watt bulb in the socket. REMOVE ALL TUBES!
Carefully power up the radio. If the bulb is dim, continue. If the bulb is bright, or arcing occurs, the transformer is seriously shorted. STOP and SHUT DOWN! Measure across the power transformer high voltage secondary. CAUTION!! High voltage!! risk of dangerous or deadly electric shock! If you have no experience working with high voltage, seek help.
If you have experience with high voltage / high current, perform the above measurement across the HV secondary (to the plate connections of the rectifier. Record the voltage. if within 20% of 500V, the Hammond will do. Measure between each leg of the secondary and the center tap. The voltages should be half the voltage across the 2 legs and be within 10% of each other. If seriously off, your short is there.
Sometimes, a transformer just fails. Other times, there is a cause. A shorted rectifier or shorted capacitors will do this.
In addition to replacing the transformer, replace all paper and electrolytic capacitors and check the rectifier tube. Yours is a 5Y4. a 5Y3 is NOT a direct replacement. The socket has to be rewired.
Add a 1 Amp fast fuse between the radio's power switch and the transformer primary. To prevent a shorted rectifier from burning out a transformer, I usually place 1N4007 silicon diodes in series between each plate pin on the rectifier socket and the transformer HV secondary, with the anode connected to the transformer wire and the cathode connected to the plate pin of the tube socket. do this for both transformer connections to the rectifier plates.
Good luck.
"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
Best Regards,
MrFixr55
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