For a long time I have been puzzled why some radios are able to receive AM radio stations in shielded and noisy environments better than others. I rotate old radios on my desk at work, which is on ground floor inside a building with stone outside walls, and steel studs in the walls. There is a large window. There are computers throughout the building, including one on my desk. I have a short wire antenna, which is routed around my desk, as far away from computer / pnone as I can get it, and runs zig - zag across the window glass. My comments apply with the venitian blind all the way up. I can only get strong local stations on most old and all new radios, whether I use my antenna arrangement, and / or the antenna loop inside the radio, as applicable. Homebuild regenerative receivers have probably worked the best. Right now I have a GE Model 321, with an internal loop, and provision for an external antenna, which I have connected. The 12SK7 has been replaced by a 12SH7, just because I have tons of them, and have acquired a lot of radios with tubes missing. So here I am in Austin Texas, listening to Waco and San Antonio - 100 miles in opposite directions. Before everybody came in this morning and turned on their computers, I was listening to Dallas, 200 miles north. Any explanation? By the way, the radio I have at work today is the old style GE 321, with an LC filter (no tuner section) between RF amp and 12SA7. It will be interesting to see how a newer style GE 321 with only RC coupling does. I will swap out rados and check next week.Ed M

That puzzles me, too. I do know that my Zenith 5-G-500 and 6-G-601 often pick up very well where other radios pick up little, if anything. Not sure why. They use Litz IF transformers and some other fine tuned arrangements, but are otherwise conventional radios.

I do know that loops often pick up better than similarily mounted long wire antennas, perhaps due to the balanced nature. A long wire will, of course, pick up well if placed outside, far from interference producing objects.

T.

Have found the same thing with a lot of radios. Some just perform better than others. It would seem some are tuned just right, and have better quality parts. The six tube sets with the RF amp front end do work a lot better than the AA5. My Motorola 67X12 and Minerva W-119 both can pull in San Francisco on there own loop antenna, and I am in San Diego. You can also perk up your radios with some hot rod tricks. Like use a 12SG7 in place of the 12SK7. This works great for a six tube set for the RF front end amp. For a 5 tube set use the 12SG7 for the IF.

:Have found the same thing with a lot of radios. Some just perform better than others. It would seem some are tuned just right, and have better quality parts. The six tube sets with the RF amp front end do work a lot better than the AA5. My Motorola 67X12 and Minerva W-119 both can pull in San Francisco on there own loop antenna, and I am in San Diego. You can also perk up your radios with some hot rod tricks. Like use a 12SG7 in place of the 12SK7. This works great for a six tube set for the RF front end amp. For a 5 tube set use the 12SG7 for the IF.
:

Certain radios definitely do perform better, regardless of the time of the day.

All of my radios can pick up distant stations (including the Majestic 180 TRF and the small Majestic International 4 tube + ballast TRF (unknown manufacturer or model number), but some just do it better. ...Zeniths especially. My 1949 Mercury radio by Zenith pulls in stations all across the nation with ease, and from Canada, too, with little interference. Of course it has a lot of interference supression built into it. I always resort to a Zenith portable when none of my other radios will pull in a signal due to interference. It'll get the job done. Both my 5 and my 6 tube Zeniths do an excellent job.

T.

:For a long time I have been puzzled why some radios are able to receive AM radio stations in shielded and noisy environments better than others. I rotate old radios on my desk at work, which is on ground floor inside a building with stone outside walls, and steel studs in the walls. There is a large window. There are computers throughout the building, including one on my desk. I have a short wire antenna, which is routed around my desk, as far away from computer / pnone as I can get it, and runs zig - zag across the window glass. My comments apply with the venitian blind all the way up. I can only get strong local stations on most old and all new radios, whether I use my antenna arrangement, and / or the antenna loop inside the radio, as applicable. Homebuild regenerative receivers have probably worked the best. Right now I have a GE Model 321, with an internal loop, and provision for an external antenna, which I have connected. The 12SK7 has been replaced by a 12SH7, just because I have tons of them, and have acquired a lot of radios with tubes missing. So here I am in Austin Texas, listening to Waco and San Antonio - 100 miles in opposite directions. Before everybody came in this morning and turned on their computers, I was listening to Dallas, 200 miles north. Any explanation? By the way, the radio I have at work today is the old style GE 321, with an LC filter (no tuner section) between RF amp and 12SA7. It will be interesting to see how a newer style GE 321 with only RC coupling does. I will swap out rados and check next week.Ed M
:

Dave,
Sounds like a good subject to expand. Both are at the mercy of alignment, but the antenna system and front end (RF amp/if any) contribute mostly to sensitivity, whereas the IF subsystem determines ultimate selectivity. Oscillator tracking must be "dead on" under all circumstances. Although it hasn't been discussed on this Forum, I'm inclined to think that AVC/AGC should be disabled in all cases for final tweaking, then performance evaluated with AVC/AGC active. Variable gain stages (RF/IF) have been discussed extensively in trade journals for years with the same conclusion. The performance of both vacuum tubes and solid state devices deteriorate rapidly when gain adjustments (bias alterations outside optimum) are applied autominously. I reserve judgement for the latest innovation of digital Radio/TV

marv

::For a long time I have been puzzled why some radios are able to receive AM radio stations in shielded and noisy environments better than others. I rotate old radios on my desk at work, which is on ground floor inside a building with stone outside walls, and steel studs in the walls. There is a large window. There are computers throughout the building, including one on my desk. I have a short wire antenna, which is routed around my desk, as far away from computer / pnone as I can get it, and runs zig - zag across the window glass. My comments apply with the venitian blind all the way up. I can only get strong local stations on most old and all new radios, whether I use my antenna arrangement, and / or the antenna loop inside the radio, as applicable. Homebuild regenerative receivers have probably worked the best. Right now I have a GE Model 321, with an internal loop, and provision for an external antenna, which I have connected. The 12SK7 has been replaced by a 12SH7, just because I have tons of them, and have acquired a lot of radios with tubes missing. So here I am in Austin Texas, listening to Waco and San Antonio - 100 miles in opposite directions. Before everybody came in this morning and turned on their computers, I was listening to Dallas, 200 miles north. Any explanation? By the way, the radio I have at work today is the old style GE 321, with an LC filter (no tuner section) between RF amp and 12SA7. It will be interesting to see how a newer style GE 321 with only RC coupling does. I will swap out rados and check next week.Ed M
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:
:
:
:It sounds to me like you could be talking about the old "selectivity vs. sensitivity" issue.
:

:Dave,
:Sounds like a good subject to expand. Both are at the mercy of alignment, but the antenna system and front end (RF amp/if any) contribute mostly to sensitivity, whereas the IF subsystem determines ultimate selectivity. Oscillator tracking must be "dead on" under all circumstances. Although it hasn't been discussed on this Forum, I'm inclined to think that AVC/AGC should be disabled in all cases for final tweaking, then performance evaluated with AVC/AGC active. Variable gain stages (RF/IF) have been discussed extensively in trade journals for years with the same conclusion. The performance of both vacuum tubes and solid state devices deteriorate rapidly when gain adjustments (bias alterations outside optimum) are applied autominously. I reserve judgement for the latest innovation of digital Radio/TV
:
:marv
:
:::For a long time I have been puzzled why some radios are able to receive AM radio stations in shielded and noisy environments better than others. I rotate old radios on my desk at work, which is on ground floor inside a building with stone outside walls, and steel studs in the walls. There is a large window. There are computers throughout the building, including one on my desk. I have a short wire antenna, which is routed around my desk, as far away from computer / pnone as I can get it, and runs zig - zag across the window glass. My comments apply with the venitian blind all the way up. I can only get strong local stations on most old and all new radios, whether I use my antenna arrangement, and / or the antenna loop inside the radio, as applicable. Homebuild regenerative receivers have probably worked the best. Right now I have a GE Model 321, with an internal loop, and provision for an external antenna, which I have connected. The 12SK7 has been replaced by a 12SH7, just because I have tons of them, and have acquired a lot of radios with tubes missing. So here I am in Austin Texas, listening to Waco and San Antonio - 100 miles in opposite directions. Before everybody came in this morning and turned on their computers, I was listening to Dallas, 200 miles north. Any explanation? By the way, the radio I have at work today is the old style GE 321, with an LC filter (no tuner section) between RF amp and 12SA7. It will be interesting to see how a newer style GE 321 with only RC coupling does. I will swap out rados and check next week.Ed M
:::
::
::
::
::It sounds to me like you could be talking about the old "selectivity vs. sensitivity" issue.
::
:
Anyway, that's my 2 cents.
Terry

Terry,
Can't comment on swapping IF cans, but seems to me that a Lattice wound coil using Litz wire would be the best choice for IF transformers. The Litz wire and Lattice technique all contribute to enhanced "Q", regardless of core shape, as long as its usable freq range (core mat'l)is adequate. The enhanced "Q", of course allows the coil to be peaked on freq, but with a narrower bandwidth, consequently enhancing the selectivity. I could go on and on about cost vs performance, but in radio of yesteryear, the bottom line was as important then as now. The Collins mechanical filter of yesteryear supposedly overcome the IF slope, enhancing selectivity, but was primarily for communication receivers, where fidelity was unimportant, but simple voice (4kHZ) communications was of the utmost.

marv

::Dave,
::Sounds like a good subject to expand. Both are at the mercy of alignment, but the antenna system and front end (RF amp/if any) contribute mostly to sensitivity, whereas the IF subsystem determines ultimate selectivity. Oscillator tracking must be "dead on" under all circumstances. Although it hasn't been discussed on this Forum, I'm inclined to think that AVC/AGC should be disabled in all cases for final tweaking, then performance evaluated with AVC/AGC active. Variable gain stages (RF/IF) have been discussed extensively in trade journals for years with the same conclusion. The performance of both vacuum tubes and solid state devices deteriorate rapidly when gain adjustments (bias alterations outside optimum) are applied autominously. I reserve judgement for the latest innovation of digital Radio/TV
::
::marv
::
::::For a long time I have been puzzled why some radios are able to receive AM radio stations in shielded and noisy environments better than others. I rotate old radios on my desk at work, which is on ground floor inside a building with stone outside walls, and steel studs in the walls. There is a large window. There are computers throughout the building, including one on my desk. I have a short wire antenna, which is routed around my desk, as far away from computer / pnone as I can get it, and runs zig - zag across the window glass. My comments apply with the venitian blind all the way up. I can only get strong local stations on most old and all new radios, whether I use my antenna arrangement, and / or the antenna loop inside the radio, as applicable. Homebuild regenerative receivers have probably worked the best. Right now I have a GE Model 321, with an internal loop, and provision for an external antenna, which I have connected. The 12SK7 has been replaced by a 12SH7, just because I have tons of them, and have acquired a lot of radios with tubes missing. So here I am in Austin Texas, listening to Waco and San Antonio - 100 miles in opposite directions. Before everybody came in this morning and turned on their computers, I was listening to Dallas, 200 miles north. Any explanation? By the way, the radio I have at work today is the old style GE 321, with an LC filter (no tuner section) between RF amp and 12SA7. It will be interesting to see how a newer style GE 321 with only RC coupling does. I will swap out rados and check next week.Ed M
::::
:::
:::
:::
:::It sounds to me like you could be talking about the old "selectivity vs. sensitivity" issue.
:::
::
:
:Most alignment service information says to turn the volume control on the set all the way up, and keep the output of the signal generator turned up just enough to get a signal on the output meter. This is to keep the AVC/AVG voltage down. The AVG lead can also be disconnected or disabled.
:
:I also agree with the point about how the IF coils are constructed. The old massive slug-tuned coils with those huge pieces of ferrite, (you know, the ones you can turn with a regular screwdriver), are A LOT less sensitive than ones using the hex driver. There have been some articles, (although I can't find one right now), about switching out IF cans to upgrade performance. I know some Hams do this to to increase selectivity in their recievers.
:Anyway, that's my 2 cents.
:Terry
:

Nothing beats a 2'X 2' loop antenna with a variable capacitor either directly coupled to, or near the radio. Lots of information on the web abut it, and simple to build and connect. You tune the radio, and then tue the antenna contraption. I can get a station or at least a carrier on every channel with my venerable philco 48-350, don't laugh it has an RF amplifier too, and always spot on with my Fisher 80. Not that there is so much to listen to any more but I can do it. I think that is the point.

:For a long time I have been puzzled why some radios are able to receive AM radio stations in shielded and noisy environments better than others. I rotate old radios on my desk at work, which is on ground floor inside a building with stone outside walls, and steel studs in the walls. There is a large window. There are computers throughout the building, including one on my desk. I have a short wire antenna, which is routed around my desk, as far away from computer / pnone as I can get it, and runs zig - zag across the window glass. My comments apply with the venitian blind all the way up. I can only get strong local stations on most old and all new radios, whether I use my antenna arrangement, and / or the antenna loop inside the radio, as applicable. Homebuild regenerative receivers have probably worked the best. Right now I have a GE Model 321, with an internal loop, and provision for an external antenna, which I have connected. The 12SK7 has been replaced by a 12SH7, just because I have tons of them, and have acquired a lot of radios with tubes missing. So here I am in Austin Texas, listening to Waco and San Antonio - 100 miles in opposite directions. Before everybody came in this morning and turned on their computers, I was listening to Dallas, 200 miles north. Any explanation? By the way, the radio I have at work today is the old style GE 321, with an LC filter (no tuner section) between RF amp and 12SA7. It will be interesting to see how a newer style GE 321 with only RC coupling does. I will swap out rados and check next week.Ed M
:

Once in awhile you come across a radio that at first don't seem like much. A Philco NT-808 is an 8 transistor radio. Has an RF amp front end, three gang tuner, tunable RF amp front end, and a three stage IF section along with a long ferrite rod antenna. Push Pull audio output. For an AM portable this set picks up everything as good as anything else. Don't seem to be a dead spot on the dial.