08-04-2024, 02:16 PM
I'm working on a Code 121 Philco 71B that has suffered extensive rodent damage underneath the chassis. I have resleeved the wiring as best I could. Bakelites have been restuffed. Electrolytic capacitors and safety caps replaced. Tubes checked and all good now (had to replace two of them). Filter capacitor metal box components have been restuffed. Micas were not replaced.
I'm able to pick up local (within 5-15 miles) stations all along the band but with low volume. The only way I can increase the volume is to place my finger on the 44 RF tube cap.
Another way to increase the volume is to jumper a lead from the antenna connection (with antenna in place) to the cap of the 44.
There is no static or squeals. Sound is pretty clean but again volume is low.
I have checked solder connections and those seem to be fine. I have checked voltages on all the tubes and they are within 5% of the specs EXCEPT I am getting a 2.56 reading on the 6.3 volt filaments. Also getting 6.6 and 7.9 voltages on the rectifier (80) 5 volt filaments. Plate voltages on the rectifier are 292 volts per plate.
Another observation is the Part No 59 (13,000 ohm-3 watt resistor) gets very hot after even a few minutes of being powered on. I replaced the big dogbone one with a smaller 3 watt resistor and it gets very hot as well. I have noted that the resistor decreases in ohms (down to 10 K or so) when it gets hot and when the set cools down, the ohms go back to nearly normal but now reads around 12,500 ohms.
On the 44 audio tube, the P-K reading is high (measures 101 (spec is 50)
Was curious if anyone has also encountered these situations and what are some things that I should now be investigating ?
I'm able to pick up local (within 5-15 miles) stations all along the band but with low volume. The only way I can increase the volume is to place my finger on the 44 RF tube cap.
Another way to increase the volume is to jumper a lead from the antenna connection (with antenna in place) to the cap of the 44.
There is no static or squeals. Sound is pretty clean but again volume is low.
I have checked solder connections and those seem to be fine. I have checked voltages on all the tubes and they are within 5% of the specs EXCEPT I am getting a 2.56 reading on the 6.3 volt filaments. Also getting 6.6 and 7.9 voltages on the rectifier (80) 5 volt filaments. Plate voltages on the rectifier are 292 volts per plate.
Another observation is the Part No 59 (13,000 ohm-3 watt resistor) gets very hot after even a few minutes of being powered on. I replaced the big dogbone one with a smaller 3 watt resistor and it gets very hot as well. I have noted that the resistor decreases in ohms (down to 10 K or so) when it gets hot and when the set cools down, the ohms go back to nearly normal but now reads around 12,500 ohms.
On the 44 audio tube, the P-K reading is high (measures 101 (spec is 50)
Was curious if anyone has also encountered these situations and what are some things that I should now be investigating ?
