07-25-2013, 07:17 PM
As Jerry said, probably the best first step would be to remove the transformer and examine it. If you are lucky, the coil wire may have broken or corroded where it is soldered to the mica compression trimmer. If this is where the break is, then cleaning the coil wire and resoldering would be the simple solution. If the break is internal to the coil, then complete replacement would be a better choice.
If the primary is indeed open but the secondary is good, then the bypass idea might work. You would have to completely disconnect the primary and replace it with a resistor or RF choke. Then connect a cap between the plate of the IF tube to the grid of the next stage. As a first try, I would use a 47K plate resistor and a 100 pF coupling cap, but you might have to experiment. The secondary trimmer would have to be adjusted to compensate for the changed loading and shunt capacitance of the bypass. Might well be worth a try if the original IF transformer can't be repaired or a replacement is unavailable.
If the primary is indeed open but the secondary is good, then the bypass idea might work. You would have to completely disconnect the primary and replace it with a resistor or RF choke. Then connect a cap between the plate of the IF tube to the grid of the next stage. As a first try, I would use a 47K plate resistor and a 100 pF coupling cap, but you might have to experiment. The secondary trimmer would have to be adjusted to compensate for the changed loading and shunt capacitance of the bypass. Might well be worth a try if the original IF transformer can't be repaired or a replacement is unavailable.
