Sound of AM back in 60s and 70s

rorban said:

Chuck said:

I don't remember that in the 1960's when AM ruled. In fact my recollection is turning the tone control up about 3/4 of the way to get more highs on a '66 Mustang radio.

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I think many people tuned the radio slightly off-center to get more highs. (This was the era of continous tunig, after all). Because the highs on many stations were not boosted and because IF slopes were mostly gentle (this was also before horrible-sounding ceramic filters were introduced in the IFs), tuning the radio off-center did not create too much objectionable distortion in envelope detectors, although there was certainly some.

Bob Orban

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Yes, this was called "tuning". And most people tuned this way. My mother tuned this way.
I remember hearing the school bus driver tune this way to sharpen up the sound over a bus full of teenagers.
Distortion begins when "not enough" of the the
"carrier" is within the curve of the response to provide reference to the sideband products. Then it's just splat.
I remember arguments in radio school that narrowband IF presentation was, of itself, frequency distortion.
And if that were the case, if side tuning and the detector/audio cicuits permitted higher response, then side tuning in fact decreased frequecy distortion as it could reproduce the original signal better. (considering roll-off as distortion, a change from the original signal, undesired in this case) Such distortion was was even advantageous in shortwave listening, etc. but antithetical to broadcast AM as taught in 1970's.

I lot of AM car radios built bass boost into a loudness tap at 40%, and the tone control started rolling off about 4000 hz.
Above the loudness tap, sound was flat if the tone was full clockwise. The rolloff was not very sharp, so you could tone down sideband noise and not impact the desired signal too much. The IFs on most of them were over 20 khz wide at -30db, so your choice at night was
10 khz squeal and highs, or trade away highs for loss of whistle.
And then sme had the highs lopped off below 10 khz anyway, but not many.

Still can't much listen to the radios with square wave RF detection and ceramic IFs. Just a fossil I guess, but at least I have happy ears.

As another "Old Fossil," I have to agree with Bob Orban that tuning the radio slightly off center yielded the best results, especially when you were fighting a lot of road noise. Back then, not every car had factory air conditioning. The old "4-60" AC system was still well in use. That stood for "four windows down at 60 mph." Even if you had AC, it was usually quite noisy.

Best AM receiver for audio is still the good old xtal diode radio like kids used to make by wrapping xformer wire around a paper towel roll. Just feed the earphone output into a real audio system. Gr8 where you can see the station.

KAAY had a great sound back in its heyday.

rorban said:

Chuck said:

I don't remember that in the 1960's when AM ruled. In fact my recollection is turning the tone control up about 3/4 of the way to get more highs on a '66 Mustang radio.

Click to expand...

I think many people tuned the radio slightly off-center to get more highs. (This was the era of continous tunig, after all). Because the highs on many stations were not boosted and because IF slopes were mostly gentle (this was also before horrible-sounding ceramic filters were introduced in the IFs), tuning the radio off-center did not create too much objectionable distortion in envelope detectors, although there was certainly some.

Bob Orban

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I definitely tuned off to the side to get more high end on AM.

me too.....geesh......the clip is awesome!

As has been suggested, I too think that the problem with AM quality today is the receivers. Back in the 70s, I really cared about the sound of our small market station. At that time, WGAR in Cleveland had the most desirable sound, to my ear. I finally called Bob Reymont who kindly explained the processing chain to me and how to get there. 1) Make sure the chain is as clean as it can be, piece by piece. 2) Process the audio with a Dorrough 310. (I think WGAR modified the crossovers, but if they did, it wasn't by much. They're only single pole filters.)

When I told him that I was impressed with how wideband his signal was, he laughed and said that that had a steep 9kHz filter to keep from splattering his neighbors. In any case, after lots and lots of work, I was able to come very close to their sound. Lots of radio people commented how great the station sounded. (None of the locals commented or cared, in retrospect.) Paul Shore at Tapecaster taught me a trick to get rid of tape skew in carts, so we never had muddy carts. Spots and current playlist were on cart.

The competitor always had an old RCA tube type limiter on its AM transmitter. That limiter had a humongous bass boost that I really liked but was never able to duplicate. I preferred the WGAR sound with the Orban 111B reverb feed from the console output to the transmitter input, bypassing the DAP.

WGAR did sound really great and had the sweetest reverb.
Faulty memory or not, I rmember hearing in radio engineering school that they somehow had received some kind
of temporary authorization for wider than normal bandwidth operation.
Why my instructor, who was the local station's engineer would make up such a story is beyond me.
Does anyone know any more details or can deny/confirm my memory.
There were a few others in that list, but WGAR sticks in my memory because I had heard them, and my brain
registered.."Oh,.... No WONDER they sound so good.."

pellmell said:

As has been suggested, I too think that the problem with AM quality today is the receivers. Back in the 70s, I really cared about the sound of our small market station. At that time, WGAR in Cleveland had the most desirable sound, to my ear. I finally called Bob Reymont who kindly explained the processing chain to me and how to get there. 1) Make sure the chain is as clean as it can be, piece by piece. 2) Process the audio with a Dorrough 310. (I think WGAR modified the crossovers, but if they did, it wasn't by much. They're only single pole filters.)

When I told him that I was impressed with how wideband his signal was, he laughed and said that that had a steep 9kHz filter to keep from splattering his neighbors. In any case, after lots and lots of work, I was able to come very close to their sound. Lots of radio people commented how great the station sounded. (None of the locals commented or cared, in retrospect.) Paul Shore at Tapecaster taught me a trick to get rid of tape skew in carts, so we never had muddy carts. Spots and current playlist were on cart.

The competitor always had an old RCA tube type limiter on its AM transmitter. That limiter had a humongous bass boost that I really liked but was never able to duplicate. I preferred the WGAR sound with the Orban 111B reverb feed from the console output to the transmitter input, bypassing the DAP.

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The 9k rolloff reminds me of WAKY's processing. Johnny Randolph recalled the set up during an interview:

The console had essentially a bass and treble control on the master output. He lowered the low end slightly and increased the end slightly. The signal fed into a marti compressor modified and averaging 30db beyond morning drive when it was set for 10db. Then he fed the audio into dynamic enhancer (marti perhaps) that rode herd around the 5k range. The signal fed into a reverb unit. Then the signal was split between a 15k and back up 8k line, he says the 8k sounded better on the air. Then at the transmitter site the signal fed into a final processor, a max combo for a while, where Randolph loaded the meter so the transmitter engineer saw a normal reading when in reality it was driven hard. Then it was fed into the daytime and nighttime transmitter. The daytime transmitter was a 10k rig running at 5kw but took advantage of unlimited positive modulation at the time.

In my neck of the woods we have a high dial position AM daytimer that has processing that is set old school. I'm not sure what they are using, a road trip is order, but it is set thick and stands out compared to the rest of the AM dial even on today's AM radio receivers.

I recently was tuning around and heard "She Loves You" by the Beatles JUMPING out of the radio at me, sounding like it
did back in the 60's. Not flat and dead, but HONKIN' an LOUD. It was KZQZ 1430 in St Loius, doing a good job getting into Chicago.
Yes, it faded some, being a graveyard frequency, but listening on the 1966 Plymouth AM/FM by Bendix, it was
very satisfying to know there are still people out there who can make a station really sing like that.

Sounded good tonight, too. Not too shabby for a 5kw directional, and I'm off in a minima.
It really shreds through the mush.

If only Chicago had this format somewhere.

Tom Wells said:

It was KZQZ 1430 in St Loius, doing a good job getting into Chicago.Yes, it faded some, being a graveyard frequency,

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Well, not OFFICIALLY a graveyard frequency (1230, 1240, 1340, 1400, 1450, 1490), but we know what you mean.

To add another, WSBC 1240 is a time brokered station here in Chicago that runs oldies in unsold slots, and they're
HONKIN', too. Just too bad I'm normally in bed these hours.
Amazing that the brokered slots sound so.....nondescript, but the station is capable of great audio.

Not sure if any of you remember the UREI BL-40's; I've had two of them in my time. One was the processor for the then WEZE 1260 in Boston. Whether it was feeding the AEL AM-10KD(the main at the time)(1979), or the backup Collins 21E, it was very smooth. The 21 E especially went well with the BL-40. I came across another one about 4 years later in Wickford RI, at the old WMYD 1370. It was fed with half of a TAPCO musical instrument EQ, then into the Harris mw-1A. That station had a lot of oomph for 500 watts non-D. WEZE was(and still is now, as WMKI)5 kW-DA-N.

Had a BL-40 feeding an 820D-2 kilowatt in Oklahoma for a while. As good as any single band processor and bewter than most. And on the Collins, 125% positive was attainable. You had to be careful not to set the phase flipper too low or it produced artifacts... and you ought to feed it a new photocell assembly every three or five years to keep it sounding smooth.

Regarding KZQZ 1430 kHz near Chicago, the NIF for the CP for Class B operation of WEEF shows a Nighttime Interference Free contour of about 32 mV/m, the only 50% exclusion station is WXNT, so that would indicate a 10% skywave of 1.6 mV/m, and without looking at any old graphs or doing any calculations, a 50% skywave of roughly half that.

Exclusion of KZQZ is 14.5 mV/m, or a 10% skywave of 0.725 mV/m, and 50% roughly half that.

Maybe KZQZ was still on day pattern when you heard it. Was it close to sunset in Chicago? That's just 2 towers and thus a much wider lobe.

For us oldtimers, I think the old call letters of KZQZ were WIL.

We had a BL-40, but we sold it because it distorted. I thought there was something wrong with the unit, but then I visited WKIX in Raleigh where Terry Tucker (if I remember correctly) showed me that they had replaced the RMS limited because it distorted. My memory's fuzzy, though.

While researching this, I came upon some other interesting information.

The WEEF CP uses the same 6 towers as the CP for WKTA (two more towers in between the longer north south dimension of the near parallelogram along I-294).

Do any of you have any thoughts on the advisability of diplexing 1330 and 1430? WKTA is just 110 night watts as I recall, but I would think that diplexing 100 kHz apart would have a serious deleterious effect on sound quality, requiring sharply tuned filters and probably assymmetric sideband frequency response. Any thoughts?

I guess it's just another unintended consequence of the FCC wanting fewer towers and collocation when it comes to AM radio stations, and the NIMBY tower attitudes. But windmill towers are OK, and cell towers continue to pop up all over. That's what doesn't make sense.

Schroedingers Cat said:

While researching this, I came upon some other interesting information.

The WEEF CP uses the same 6 towers as the CP for WKTA (two more towers in between the longer north south dimension of the near parallelogram along I-294).

Do any of you have any thoughts on the advisability of diplexing 1330 and 1430? WKTA is just 110 night watts as I recall, but I would think that diplexing 100 kHz apart would have a serious deleterious effect on sound quality, requiring sharply tuned filters and probably assymmetric sideband frequency response. Any thoughts?

I guess it's just another unintended consequence of the FCC wanting fewer towers and collocation when it comes to AM radio stations, and the NIMBY tower attitudes. But windmill towers are OK, and cell towers continue to pop up all over. That's what doesn't make sense.

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Diplexing could be done, but it's for sure you'll fight some images and likely mixing of audio.
In Chicago there is really nice image of 720 WGN "off of" AM 820 ( whatever call they are now ) on 920, and they arent even co-located.
It's just an actual "mixed in air" image regardless of radio use, and not even occurring in the near field area, but about 10 miles away from each.
I tried to do 2 part 15 AMs for stereo and it was pretty annoying to fight the birdies.

Above post:
Make that "regardless of radios used".

What if...now think about this...what if two stations were to diplex into the same sticks and they were...ready...and they were 45 or 46 channels apart.