:After my 37-660 Philco is on for 30 minutes or longer the pwr. transformer and power supply choke get real warm. The choke is drawing 170ma dc. Is that too high?
::170 mA sounds pretty high. This radio has P-P 6F6 output tubes rated for 10 Watts. It seems to me that your total DC current should be well under 100 mA. Look for a shorted filter cap or a resistor that has changed value. Have you checked all the tubes? You can get a schematic on Nostalgia Air (Resources). Does the radio have sound output? Is it distorted? Good luck!
::Rich
::
:Rich, The radio plays just fine, no distortion. I have changed caps in the pwr supply all are new. When I pull both audio output tubes out there is still 90ma dc current through the pwr. supply choke. I also found two resistors in the power supply that had changed value and I replaced them but still has high current. John
:::After my 37-660 Philco is on for 30 minutes or longer the pwr. transformer and power supply choke get real warm. The choke is drawing 170ma dc. Is that too high?
That said, you should still replace all drifted resistors. For perfect radio performance, all components must function like new. A drifted resistor is often caused by overheating. This can be caused by either an undersized resistor (wattage) selected by the factory, or by a failing condenser (or other part), causing too much current to be drawn through the resistor. If a resistor drifted heavily, look for a shorted or leaky condenser in that circuit. If the condenser is not heavily shorted, but just slightly leaky, it should still be replaced, as a small leak carries carbon and metal molecules, which will eventually build into a large leak. For optimum radio performance both in fidelity and safety, no condenser can have any leakage of any kind....not even several million ohms. There must be NONE. Even if a condenser is not dripping wax, it should be tested thoroughly, removed from the circuit.
Of course, don't think that condensers alone can cause your overheating. It could be an IF transformer or other RF transformer in which the high voltage primary has shorted somehow to the secondary, or it could be a metal enclosed wire wound resistor that has developed a leak from the wire to the metal case, and there-on to the chassis. The former trouble with the IF transformer usually leaves the set lifeless, so if your set works, that trouble is not likely.
:Just a tip....when resistors drift, they usually drift higher in value (carbon composition). Replacement of a drifted resistor will decrease the value back to original. A lower value will cause MORE current draw.
:
:That said, you should still replace all drifted resistors. For perfect radio performance, all components must function like new. A drifted resistor is often caused by overheating. This can be caused by either an undersized resistor (wattage) selected by the factory, or by a failing condenser (or other part), causing too much current to be drawn through the resistor. If a resistor drifted heavily, look for a shorted or leaky condenser in that circuit. If the condenser is not heavily shorted, but just slightly leaky, it should still be replaced, as a small leak carries carbon and metal molecules, which will eventually build into a large leak. For optimum radio performance both in fidelity and safety, no condenser can have any leakage of any kind....not even several million ohms. There must be NONE. Even if a condenser is not dripping wax, it should be tested thoroughly, removed from the circuit.
:
:Of course, don't think that condensers alone can cause your overheating. It could be an IF transformer or other RF transformer in which the high voltage primary has shorted somehow to the secondary, or it could be a metal enclosed wire wound resistor that has developed a leak from the wire to the metal case, and there-on to the chassis. The former trouble with the IF transformer usually leaves the set lifeless, so if your set works, that trouble is not likely.
:It's a puzzler, since the set seems to work. I wonder if the speaker field could have a short to ground. Can you unplug the speaker and measure the total load current? I guess if that doesn't work, you will have to check the plate current in each stage. I assume your B+ is about 300V. Since the audio output is rated at 10 watts, I would assume that idling current to the output tubes should be about 30 mA. The speaker field is about 2200 ohms in series with a 7750 ohm resistor. That combination should also pull about 30 mA. There are 6 other tubes, that might draw 5 mA. each. Your total current should be about 90 or 100 mA when idling and maybe 125 mA. with full audio output, so 170 mA seems high.
:
:
::Just a tip....when resistors drift, they usually drift higher in value (carbon composition). Replacement of a drifted resistor will decrease the value back to original. A lower value will cause MORE current draw.
::
::That said, you should still replace all drifted resistors. For perfect radio performance, all components must function like new. A drifted resistor is often caused by overheating. This can be caused by either an undersized resistor (wattage) selected by the factory, or by a failing condenser (or other part), causing too much current to be drawn through the resistor. If a resistor drifted heavily, look for a shorted or leaky condenser in that circuit. If the condenser is not heavily shorted, but just slightly leaky, it should still be replaced, as a small leak carries carbon and metal molecules, which will eventually build into a large leak. For optimum radio performance both in fidelity and safety, no condenser can have any leakage of any kind....not even several million ohms. There must be NONE. Even if a condenser is not dripping wax, it should be tested thoroughly, removed from the circuit.
::
::Of course, don't think that condensers alone can cause your overheating. It could be an IF transformer or other RF transformer in which the high voltage primary has shorted somehow to the secondary, or it could be a metal enclosed wire wound resistor that has developed a leak from the wire to the metal case, and there-on to the chassis. The former trouble with the IF transformer usually leaves the set lifeless, so if your set works, that trouble is not likely.
Your 462 ohm field was probably originally designed to feed both the radio and the output tubes of another radio. That is why the low resistance was chosen. There would be about a 60 volt drop with 4 or 5 RF and AF tubes, and 2 output tubes in push-pull (such as 6F6 or 6K6). It is probably designed to handle a lot of current, but since it is only feeding the RF tubes in this radio, it does not drop the voltage enough, which causes the RF and AF tubes to use this excess voltage, which causes an excess load on the transformer and choke.
Anyway, place a resistor in series with the field. If the radio performs well, then everything is fine. It is slightly possible that the field will be weak, as it was most likely originally designed to handle a lot more current. Check and see if there is about a 40 to 60 volt drop across it (drop just across the field, not the field and resistor) with the new resistor in series. If the voltage drop is somewhat reasonable, and the field pull (on a screw driver or something like that) seems strong, then everything is likely okay. Before you assume that the field is not strong enough, make sure all audio and RF stages are in good order. You should be able to operate the radio loudly with no distortion. Turning up the radio only to get quiet distorted music is a sign that the field is not energized enough.
The other thing you could do, which would be slightly radical, is place the field where the choke is, and then place the choke where the field was, with additional resistance in series to equal the original field's resistance (2200 ohms). Placing the 6F6 tubes on the field load will make the field stronger. However, placing the 462 ohm field in place of the 175 ohm choke will slightly decrease voltage to the 6F6 tubes. Then, when you operate the radio, you'd want to observe the field to see that it didn't get too warm, so that you knew that it could handle the total current rating of the radio. It likely can, but you just want to be sure. At any rate, this would surely energize the field enough.
Thomas
:Well, someone correct me if I'm wrong. Here's what I see: The current from the rectifier flows first through the choke and then through the field coil. Just prior to the field coil, current for the output tube plates is taken. From the field coil it goes to the rest of the radio and also to the 7.75K resistor. This resistor puts a load on the field to keep the voltages to the rest of the radio at a given value. Increasing its resistance will only increase the voltages to the rest of the radio, which could be detrimental. Decreasing its resistance will both decrease voltages to the rest of the radio (something you also don't want), and also put an even heavier load on the power supply, field, and choke. That said, leave this resistor alone. The only practical thing you can to, and still use the speaker you're using, is to put an additional resistance in series with the field so that the total resistance is the same as the original speaker. Use either a 10 or 20 watt resistor, which ever runs cool enough for your needs. A 10 will likely work, as you are only feeding the RF stages. If you cannot obtain a 20 watt resistor, place two 10 watt resistors of double the needed value in parallel.
:
:Your 462 ohm field was probably originally designed to feed both the radio and the output tubes of another radio. That is why the low resistance was chosen. There would be about a 60 volt drop with 4 or 5 RF and AF tubes, and 2 output tubes in push-pull (such as 6F6 or 6K6). It is probably designed to handle a lot of current, but since it is only feeding the RF tubes in this radio, it does not drop the voltage enough, which causes the RF and AF tubes to use this excess voltage, which causes an excess load on the transformer and choke.
:
:Anyway, place a resistor in series with the field. If the radio performs well, then everything is fine. It is slightly possible that the field will be weak, as it was most likely originally designed to handle a lot more current. Check and see if there is about a 40 to 60 volt drop across it (drop just across the field, not the field and resistor) with the new resistor in series. If the voltage drop is somewhat reasonable, and the field pull (on a screw driver or something like that) seems strong, then everything is likely okay. Before you assume that the field is not strong enough, make sure all audio and RF stages are in good order. You should be able to operate the radio loudly with no distortion. Turning up the radio only to get quiet distorted music is a sign that the field is not energized enough.
:
:The other thing you could do, which would be slightly radical, is place the field where the choke is, and then place the choke where the field was, with additional resistance in series to equal the original field's resistance (2200 ohms). Placing the 6F6 tubes on the field load will make the field stronger. However, placing the 462 ohm field in place of the 175 ohm choke will slightly decrease voltage to the 6F6 tubes. Then, when you operate the radio, you'd want to observe the field to see that it didn't get too warm, so that you knew that it could handle the total current rating of the radio. It likely can, but you just want to be sure. At any rate, this would surely energize the field enough.
:
:Thomas