11-26-2021, 06:40 PM
Connect your generator to the grid cap of the 1st 77 & gnd. Set it to 460kc with a modulated tone. Use an insulated tool to peak #s 11 and 15. # 11 has hv on it. As the signal gets stronger back down the output from the generator so you don't overload he detector. Next adjust the sensitivity cap #17 till the the IF starts to oscillates then back it out 1/4 of a turn or a little less for sharper selectivity.
Two other stages are suspect the local oscillator (lo) and the antenna input circuit.
To check the lo use a small radio with a loop ant near the 1st 77 tube. Tune the small set 460kc higher than the dial on the 84. If a is well you should hear a hiss or a squeal in the small set. For instance tune the 84 to 100 (1000kc) in listen in the small set while you are holding near the 77 to 1460kc. You should be able to track it all the way down to 540kc by tuning both sets. If it's not oscillating most of the time it's the feedback winding on the coil has rotted (green dots). If it has been rewound and is not working it's been wound in the wrong direction or the wrong # of turns.
The ant circuit is pretty simple. There must be a short or open in the primary of the ant coil or the volume control/wiring. Unplug the set. turn he volume full up and measure the resistance from the ant post to ground post. Should see about a few ohms. If you see a high resistance there's an issue with the coil/winding being open. If it's lower than an ohm or so I'd look for a short.
Two other stages are suspect the local oscillator (lo) and the antenna input circuit.
To check the lo use a small radio with a loop ant near the 1st 77 tube. Tune the small set 460kc higher than the dial on the 84. If a is well you should hear a hiss or a squeal in the small set. For instance tune the 84 to 100 (1000kc) in listen in the small set while you are holding near the 77 to 1460kc. You should be able to track it all the way down to 540kc by tuning both sets. If it's not oscillating most of the time it's the feedback winding on the coil has rotted (green dots). If it has been rewound and is not working it's been wound in the wrong direction or the wrong # of turns.
The ant circuit is pretty simple. There must be a short or open in the primary of the ant coil or the volume control/wiring. Unplug the set. turn he volume full up and measure the resistance from the ant post to ground post. Should see about a few ohms. If you see a high resistance there's an issue with the coil/winding being open. If it's lower than an ohm or so I'd look for a short.
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
