10-23-2022, 08:22 PM
>tried the sg at 460, radio about 550 but didn't get a tone
So did you try adjusting #20 and #11 to/till find the signal at 460KC? If not give that a try. Turn the signal output level up to high till you find the 460kc signal. Then go back and forth between the two trimmers IF for max signal with a low output setting on the generator. Then use #21 to set the level for max sensitivity by turning it inward till it starts to squeal. Then back it out a turn. You may find that when you adjust 20 & 11 the IF will start to oscillate. If so then back out 21 a little and continue to adjust 20 & 11. Conversely if the IF sensitivity is really poor screw in #21 a little after you find the 460kc signal. Then continue to adjust 20 &11.
I'm not sure if the 80 and the 81 use a fiber adjustment nut on the sensitivity control #21 like the later models do. The fiber nut are somewhat delicate and will crack and break when tighten. If it's tapered and looks like all of the other adjuster it's probably brass. If it's squared off on the end and has a screwdriver slot in it it's the fiber nut. Just be gentle when tightening. It doesn't have to be anywhere near tight when it's adjusted.
The voltages around the mixer look good but the cathode is a bit high. We can put a pin in it for now as it may have to do with the osc. It's low enough that it's drawing plate current. The detector voltages are kinda off but that could be because it not working and not near the point of oscillation. I'm assuming you've checked resistors #23 #25 #22. They are a common fault in the 80, 81, and 84's.
So did you try adjusting #20 and #11 to/till find the signal at 460KC? If not give that a try. Turn the signal output level up to high till you find the 460kc signal. Then go back and forth between the two trimmers IF for max signal with a low output setting on the generator. Then use #21 to set the level for max sensitivity by turning it inward till it starts to squeal. Then back it out a turn. You may find that when you adjust 20 & 11 the IF will start to oscillate. If so then back out 21 a little and continue to adjust 20 & 11. Conversely if the IF sensitivity is really poor screw in #21 a little after you find the 460kc signal. Then continue to adjust 20 &11.
I'm not sure if the 80 and the 81 use a fiber adjustment nut on the sensitivity control #21 like the later models do. The fiber nut are somewhat delicate and will crack and break when tighten. If it's tapered and looks like all of the other adjuster it's probably brass. If it's squared off on the end and has a screwdriver slot in it it's the fiber nut. Just be gentle when tightening. It doesn't have to be anywhere near tight when it's adjusted.
The voltages around the mixer look good but the cathode is a bit high. We can put a pin in it for now as it may have to do with the osc. It's low enough that it's drawing plate current. The detector voltages are kinda off but that could be because it not working and not near the point of oscillation. I'm assuming you've checked resistors #23 #25 #22. They are a common fault in the 80, 81, and 84's.
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!
Terry
