10-27-2008, 05:16 PM
Newbies experience with 46-350 Philco Radio. Actually I have been dabbling for 40 years, but am approaching retirement and have found restorations a relaxing hobby. For about $25 (delivered) you can get one of these great wooden AC/DC and battery portables on Ebay. Talk about sensitive, they have an RF amp in addition to the the AA5 lineup of the day. We're talking 1946, although there are a many 1948 models out there as well and they are about the same.
So I got my first specimen, and immediately replaced "all" the caps except the micas, and even dutifully dug out the gunk of the filter caps and stuffed them. Tubes were OK, and the cabinet needed TLC, actually it looked rough. By the way, if the leatherette is bad, you can carefully peel it off, sand and stain the sides to agree with the front, and finish with laquer or shellac. The side wood is soft, and what I did was cover it with grain filler, lightly sand it, and then took some oil artist's paint and dabbed on color and blended it.
It played beautifully for a week or two. Then, started to fade into nothing a minute or two after powering up. I thought the cathode capacitor to the 3LF4 was bad, even though it was a new one and was stuffed into the can, and disconnected it and jumped a new one in it's place. Well, I missed by one terminal strip and managed to destroy 3 of the six tubes. Thank God I don't do this for a living. After a new 3LF4, 1T4, and of course the 1S4, the radio played, but was picking up only a few stations, and behaving badly. Now I know what to do with the second specimen I picked up, a 1948 model, and I converted to 6 volt tubes. It plays poorly, and there is trouble in the converter circuit. I'll be opening up that same coil and inspecting Mr. 10 mmf next weekend.
I measured the antenna coil, and it was on the mark for ohms. Swapped out the 1T4 RF amp with no improvement. Aligned the IF and RF with my old reliable Superior Genometer, checked the wiring again, no glaring mistakes, and of course, it worked fine in the beginning. Holmes to the rescue. The most likely villian was not the butler, but the 10 mmf capacitor that bridges the primary and secondary coil between the RF and the first IF. But they never go bad, was my first conslusion. Wrong. I unscrewed the cover, and unsoldered the part, and measured it with my digital ohm-meter, Nearly infinite resistance. Now, I hooked it up to my ancient eico capacitance tester, and found it to be a dead short at any voltage. So much for instruments. I found a 10 mmf 500 volt cylindrical cap (probably a ceramic version) in my drawer, also probably older than I am, soldered it up, and the machine lives. I cracked open the the old cap in my vice, and can see crud inside. So, mica disease does not always cause 'thunderstorms,' they can nonetheless send you on a wild goose chase. I will probably replace the caps inside the second IF transformer, and the bogie, the one across the loop antenna as well.
And by the way, I added a 240 ohm 5 watt resistor to the final filament chain to keep the voltage to the string below 9 volts, as I used a little larger value caps when stuffing the can. I am in no rush to find replacement tubes again. The resistor must be larger if you decide to eliminate the rectifier tube, and go with a diode instead. And if you do so, you must also respect the upper plate limits of the 3LF4. I now have 8.75 volts on the 9 volt string, which I think is about right.
One more thing, most of the speakers can be adjusted so that the voice coil moves freely. I use fabric glue to fix tears, better yet, the glue they send along with replacement surrounds.
So I got my first specimen, and immediately replaced "all" the caps except the micas, and even dutifully dug out the gunk of the filter caps and stuffed them. Tubes were OK, and the cabinet needed TLC, actually it looked rough. By the way, if the leatherette is bad, you can carefully peel it off, sand and stain the sides to agree with the front, and finish with laquer or shellac. The side wood is soft, and what I did was cover it with grain filler, lightly sand it, and then took some oil artist's paint and dabbed on color and blended it.
It played beautifully for a week or two. Then, started to fade into nothing a minute or two after powering up. I thought the cathode capacitor to the 3LF4 was bad, even though it was a new one and was stuffed into the can, and disconnected it and jumped a new one in it's place. Well, I missed by one terminal strip and managed to destroy 3 of the six tubes. Thank God I don't do this for a living. After a new 3LF4, 1T4, and of course the 1S4, the radio played, but was picking up only a few stations, and behaving badly. Now I know what to do with the second specimen I picked up, a 1948 model, and I converted to 6 volt tubes. It plays poorly, and there is trouble in the converter circuit. I'll be opening up that same coil and inspecting Mr. 10 mmf next weekend.
I measured the antenna coil, and it was on the mark for ohms. Swapped out the 1T4 RF amp with no improvement. Aligned the IF and RF with my old reliable Superior Genometer, checked the wiring again, no glaring mistakes, and of course, it worked fine in the beginning. Holmes to the rescue. The most likely villian was not the butler, but the 10 mmf capacitor that bridges the primary and secondary coil between the RF and the first IF. But they never go bad, was my first conslusion. Wrong. I unscrewed the cover, and unsoldered the part, and measured it with my digital ohm-meter, Nearly infinite resistance. Now, I hooked it up to my ancient eico capacitance tester, and found it to be a dead short at any voltage. So much for instruments. I found a 10 mmf 500 volt cylindrical cap (probably a ceramic version) in my drawer, also probably older than I am, soldered it up, and the machine lives. I cracked open the the old cap in my vice, and can see crud inside. So, mica disease does not always cause 'thunderstorms,' they can nonetheless send you on a wild goose chase. I will probably replace the caps inside the second IF transformer, and the bogie, the one across the loop antenna as well.
And by the way, I added a 240 ohm 5 watt resistor to the final filament chain to keep the voltage to the string below 9 volts, as I used a little larger value caps when stuffing the can. I am in no rush to find replacement tubes again. The resistor must be larger if you decide to eliminate the rectifier tube, and go with a diode instead. And if you do so, you must also respect the upper plate limits of the 3LF4. I now have 8.75 volts on the 9 volt string, which I think is about right.
One more thing, most of the speakers can be adjusted so that the voice coil moves freely. I use fabric glue to fix tears, better yet, the glue they send along with replacement surrounds.
