01-18-2011, 11:52 AM
The loop antenna measures 3 ohms, I will try swapping the 7A8 to see if that makes a difference. None of the coils are open. Z1 adjustment doesn't affect the reception with the limited range I can turn it (about 1 turn). The slug is pretty much frozen if I try to go beyond 1 turn. I certainly don't want to crack the slug or break the coil support. I'll have to disassemble Z1 to free up the slug.
I pulled the second IF transformer. Take a look at the photos. The mica had extensive silver migration. Looks like I'll be removing the old mica caps on the first IF and Z1. When I used 100pf capacitors across the coils, I could not adjust the coils to 455KHz. 490KHz was the lowest I could get. I should be able to get some 110pf caps today and see if that doesn't get me into the 455KHz range. I tested the transformer with my signal generator attached via a 47K resistor to the primary coil. The DVM then read the voltage developed by the diode connected to a 0.01ufd cap on the secondary coil.
[Image: http://www-rohan.sdsu.edu/~nash/philco/2nd%20IF.jpg] [Image: http://www-rohan.sdsu.edu/~nash/philco/2...opened.jpg] [Image: http://www-rohan.sdsu.edu/~nash/philco/2...20mica.jpg]
I pulled the second IF transformer. Take a look at the photos. The mica had extensive silver migration. Looks like I'll be removing the old mica caps on the first IF and Z1. When I used 100pf capacitors across the coils, I could not adjust the coils to 455KHz. 490KHz was the lowest I could get. I should be able to get some 110pf caps today and see if that doesn't get me into the 455KHz range. I tested the transformer with my signal generator attached via a 47K resistor to the primary coil. The DVM then read the voltage developed by the diode connected to a 0.01ufd cap on the secondary coil.
[Image: http://www-rohan.sdsu.edu/~nash/philco/2nd%20IF.jpg] [Image: http://www-rohan.sdsu.edu/~nash/philco/2...opened.jpg] [Image: http://www-rohan.sdsu.edu/~nash/philco/2...20mica.jpg]
