01-17-2023, 04:33 PM
Hi Mr. Big,
If you replaced the electrolytic caps, you can take the dim bulb out of the circuit.
It is good to fuse the hot side of the power to the radio. However, it is not as necessary as fusing a radio containing a power transformer. The heater tap of the 35Z5 serves as the fuse. Since the plate of the rectifier is connected to the tap in the heater, any short in the tube or the B+ circuit will cause the entire current load of the short to present itself between the line and the tap, causing the heater to burn out, stopping the current flow. However, a fuse is usually cheaper than a 35Z5, so good on you for installing the fuse.
You definitely want to have the power switch on the "hot" side rather than the return side for safety. I don't know why the manufacturers insisted on putting the switch "on the low side" of the line. Maybe to lessen hum, but in that mode, if the switch is on the low side and the power is off, then the chassis becomes "hot" through the tube heaters which have a low resistance when cold. Even though there is a cap and resistor to limit shock, it is still possible.
Did you measure the 12SA7 Pin 5 voltage while actually receiving a signal? If so, did you lose the signal when attempting the measurement?
Do you have another AA5 type radio. Locate it next to this one and attempt to tune stations. If you receive more stations on this "test" radio, then yes, you have issues with the one you are repairing.
Try running a feeler gauge between the plates of the capacitor when they are fully meshed (Radio set for 530KHz).
At this point, I would avoid getting the tuning capacitor all wet bathing it in DeOxIt. The stuff is expensive anyway. concentrate on the bearings and the spring that grounds the rotor of the tuning cap.
Try to disconnect the leads between the tuning cap and the rest of the circuit, then use an ohmmeter and check resistance between rotor and stator for each section of the tuning cap while sweeping the band. The cap must read "open" at all times. Seeing anything other than infinite resistance indicates that the cap is intermittently shorting, from any surface corrosion "fuzz" between the rotor and stator plates. It is important to disconnect the connections at the stator otherwise you will be reading the resistance of the coils that parallel the capacitor.
Best of luck with this. There are many experts willing to help you conquer this and preserve a piece of history.
If you replaced the electrolytic caps, you can take the dim bulb out of the circuit.
It is good to fuse the hot side of the power to the radio. However, it is not as necessary as fusing a radio containing a power transformer. The heater tap of the 35Z5 serves as the fuse. Since the plate of the rectifier is connected to the tap in the heater, any short in the tube or the B+ circuit will cause the entire current load of the short to present itself between the line and the tap, causing the heater to burn out, stopping the current flow. However, a fuse is usually cheaper than a 35Z5, so good on you for installing the fuse.
You definitely want to have the power switch on the "hot" side rather than the return side for safety. I don't know why the manufacturers insisted on putting the switch "on the low side" of the line. Maybe to lessen hum, but in that mode, if the switch is on the low side and the power is off, then the chassis becomes "hot" through the tube heaters which have a low resistance when cold. Even though there is a cap and resistor to limit shock, it is still possible.
Did you measure the 12SA7 Pin 5 voltage while actually receiving a signal? If so, did you lose the signal when attempting the measurement?
Do you have another AA5 type radio. Locate it next to this one and attempt to tune stations. If you receive more stations on this "test" radio, then yes, you have issues with the one you are repairing.
Try running a feeler gauge between the plates of the capacitor when they are fully meshed (Radio set for 530KHz).
At this point, I would avoid getting the tuning capacitor all wet bathing it in DeOxIt. The stuff is expensive anyway. concentrate on the bearings and the spring that grounds the rotor of the tuning cap.
Try to disconnect the leads between the tuning cap and the rest of the circuit, then use an ohmmeter and check resistance between rotor and stator for each section of the tuning cap while sweeping the band. The cap must read "open" at all times. Seeing anything other than infinite resistance indicates that the cap is intermittently shorting, from any surface corrosion "fuzz" between the rotor and stator plates. It is important to disconnect the connections at the stator otherwise you will be reading the resistance of the coils that parallel the capacitor.
Best of luck with this. There are many experts willing to help you conquer this and preserve a piece of history.
"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
Best Regards,
MrFixr55
