![]() |
|
#1
|
||||
|
||||
|
Looking for help with first chassis restore.
I acquired my first antique radio, a Philco 39-25, a few weeks back. In my inexperience I plugged it into an ac outlet and although the radio didn't tune any stations, I was able to plug in a CD player and a guitar through an RCA jack on the back and get good sound out of the speaker without any hum.
So after learning a little more about good chassis restoration practices I ordered all new caps to replace the paper and wax including some safety caps for the line-filter capacitors bakelite block. While waiting for my caps to arrive I built a dim bulb tester. Now I wish I had taken the time to test the radio after replacing each cap, but I didn't. Nor did I test each new cap. I just replaced them all, rebuilt the bakelite block and replaced the power cord. I don't have a tube tester, but the tubes were working when I got the radio (at least enough to be amplifying and outputing whatever I fed through its inputs). So after the recap I plugged it into my dim bulb tester and the bulb glows brightly. I've double checked all the connections and don't see any place where a short would occur. I've verified that my rebuild of the bakelite block in the power circuit is correct. I read somewhere that a bright bulb right away will indicate a short in the transformer. How do I go about troubleshooting from this point? I'm worried that a bad cap went in. Can I test the caps without taking a lead off or do I have to begin desoldering those and testing? Should I be looking at the power stage/circuit first or could a cap anywhere cause this condition? Do I need to start checking resistors - if so where might be a good place to start? In a previous service of this radio two of the electrolyte cans were bypassed, but the third was not. I bypassed the third (part 18) by putting a new electrolyte cap in its place. There was only one wire coming out of the center of that can. I connected the replacement cap's positive lead to the same place that the wire was connected and because the can's base was not insulated from the chassis I assumed that the caps inside were grounded to the can and connected the negative end of my new cap to the base of the can. The only other descrepancy I'm aware of is that the .006mF cap (part 36) was replaced by a .05mF cap. I didn think that could that cause a short though. I've attached the schematic for convenience/reference. Any suggestions, tips, advice is welcome and much appreciated. Last edited by BostonDave; 04-30-2009 at 09:47 AM. |
|
|