05-26-2021, 09:10 AM
To answer your last post you pose an interesting question. Sensitivity. I guess it depends on how you judge it. Techs would say hook it to a SG with a calibrated attenuated output and do the limbo with it. Some may have a 5' piece of wire in their basement that they call an ant. All of their set that don't have a loop ant have poor sensitivity. Others have a hundred feet+ of wire up in the air and a lightning arrester. A separate earth ground rod. All their sets work dandy. A marginal set with a good ant can perform pretty good. Same with a good set and a lousy ant. But neither is the best situation.
I'm not sure if I've ever had a set that had poor sensitivity that was do to it age or design. It would end up being a part failure or a failed repair. Heck you can go back to the late teens and 1920's when regenerative sets were king. One or two tube sets that had all kinds of sensitivity. You might want to look into building one for fun. They are simple and will give you a good working knowledge of how an oscillator works, hand capacitance, and inductive coupling to name a few.
I find that the early70 is a little beastly because of it's lack of avc. Don't have a working 70B but do have a 370. It's playing as I type. It has a 15' wire that runs behind the couch. Picks up all the local stations with good fidelity. Don't like the knob setup, hard to grip, it's very different from the 70B.
The 90 yr old technology works ok if you use the sort of antenna that was used back then. This is if all is in good working order. With that being said we have a lot of "new problems" to deal with that were not around back then.
One thing I forgot to mention the open ant coil will also effect the volume control. With a good ant and the volume all the way down you'll still hear stations. The 5000 ohm section of the vc is to shunt all of the signal to ground when the control is turned all the way to the left.
Now just for test purposes wink wink you could connect a small cap like 5 or 10mmfd from the ant post to grid cap of the 24A rf amp. Voltage rating whatever lightning is.
Sorry went into the ramble mode...
I'm not sure if I've ever had a set that had poor sensitivity that was do to it age or design. It would end up being a part failure or a failed repair. Heck you can go back to the late teens and 1920's when regenerative sets were king. One or two tube sets that had all kinds of sensitivity. You might want to look into building one for fun. They are simple and will give you a good working knowledge of how an oscillator works, hand capacitance, and inductive coupling to name a few.
I find that the early70 is a little beastly because of it's lack of avc. Don't have a working 70B but do have a 370. It's playing as I type. It has a 15' wire that runs behind the couch. Picks up all the local stations with good fidelity. Don't like the knob setup, hard to grip, it's very different from the 70B.
The 90 yr old technology works ok if you use the sort of antenna that was used back then. This is if all is in good working order. With that being said we have a lot of "new problems" to deal with that were not around back then.
One thing I forgot to mention the open ant coil will also effect the volume control. With a good ant and the volume all the way down you'll still hear stations. The 5000 ohm section of the vc is to shunt all of the signal to ground when the control is turned all the way to the left.
Now just for test purposes wink wink you could connect a small cap like 5 or 10mmfd from the ant post to grid cap of the 24A rf amp. Voltage rating whatever lightning is.
Sorry went into the ramble mode...
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
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