Hello, Working on a Philco 37-89. I needed to take out the 1st IF because 2 wires were falling apart. The schematic (Riders 7-29) shows only 4 wires. The black wires in the picture are the ones with bad insulation. They are not on the schematic. One wire goes to pin 5 of the 6K7 (IF) tube and the other goes to ground. There is no other wire connected to pin 5 but the schematic shows pin 5 going to ground. I ohm out the black wires and I get about .3 ohm. It looks to me like the black wires are wrapped around the core abut 2 times. Any idea what this is for? It is going to be tricky getting new wires on there. Looks like I will just splice as far in as I can. There is nothing like that on the 2nd IF.
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Ah I might have known there would be a different schematic. My chassis does not have a label stating what model or run it is. All I had was the tube chart in the cabinet. Thank you.
Mostly the difference between the '37 an '38 model chassis is the conversion to octal from standard based tubes. I suspect that the loop is used to add a little bit feedback to the IF amp stage. This in turn boosts the gain. A lot of pentode IF amp tubes the suppressor grid and cathode are internally connected so this sort circuit couldn't be used. Phasing is important without it no feedback will happen
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
