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fm Processing in the 1950s and 1960s

M

mgpt6

Hi folks, i was wondering what units were popular in the 1950s and 1960s for FM processing. I am sure most,if not all units were tube units. Also, when stereo was first started in 1961 was there a new AGC/peak limiter units for stereo or were 2 mono units used for each channel? How many tubes were used in the early 1st FM stereo generators in the early 60s?
Also, did many stations have better sounding AMs because many stations simulcast the same program on the both AM and FM until FCC ruled you could not do that in the late 60s?
 
mgpt6 said:
Also, did many stations have better sounding AMs because many stations simulcast the same program on the both AM and FM until FCC ruled you could not do that in the late 60s?
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You have phrased your question in an unusual way. It is what a lawyer trying a case might call "a leading question". If you are suggesting that AM stations that established an FM station ended up with a better sounding AM because the presence of an FM station caused and/or required better audio, the answer is NO as I experienced it. Granted I was in the heartland of rural America for most of that period, not in places like NYC, Chicago or Los Angeles.

Today's younger generation cannot imagine how good many AM stations of that era sounded, with or without an FM in the family. (Yes, some of the AMs had pathetic audio and I could name names if it served any purpose.) I can also name names of AM stations that were "ego trips" for owners who also had a First Phone licenses, many of whom were much better engineers than they were salesmen or business tacticians. I remember visiting a station in the late 1950s where the two partners were both engineers and they recited the laundry list of customizations that had created for their transmitter and how many dB of reduced noise level each one accomplished. The day I was there they were beside themselves. That very week they had unbolted the power supply of their A.M. transmitter, lifted it up, and slid a foam rubber pad underneath the power supply. They got another 2 or 3 dB of reduced noise because the power supply was no longer vibrating the entire case of the transmitter, reducing the pickup of vibration noised by the tubes in the audio chain.

I thought that was the ultimate in what today is called "anal retentive". But the man I was working for at the time some 30 miles from them was in their league. In probably what was the second ugliest radio station I ever worked for, we had a number of innovations on a par with the "foam rubber mattress" brigade. ;D

In the heartland of America many of the FM stations were "place-holders". Here is what was happening: The fool channels are available. We don't know what to do with them but smart people claim the future is in those channels. So we have to get the license and drag it along like dead weight so someone else doesn't nail it down while we are looking the other way. There was nothing exotic about the audio processing chain in the FM stations that I saw or worked for in that era. Exceptions existed and others who saw them and experienced them can post about them.
 
frankberry said:
As I recall, in the 50s and 60s, most FM stations operated with little or no processing.
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For the most part, most AM/FM combos in the 50's and 60's had the FM side taking a "tap" off of the AM's side's processing. It was neat, quick and dirt cheap. Before FM Stereo came about in 1961, as long as the FM side had some basic processing (preventing "overshoots"), all was fine with the world. However, when Stereo came, the stations had to be very diligent to make sure the FM Stereo modulation stayed within the FCC prescribed limits in terms of modulation. Since most non-simulcast FM's were of the classical or "Mantovani" ilk, the stations took great pains to keep it clean and crisp with the use of a CBS Volumax with a companion AGC unit in front of it. For Stereo, they simply doubled up on the units either individually or "linked". Once FM went to a more popular genres of music, such as stations like WRKO-FM, WOR-FM and so on, FM processing took a different route and the rest was history.
 
Interesting you should ask.. KGHO was a simulcast AM/FM started about 1963. There were probably less than 50 FM recievers in Western Washington then. The AM had a Gates "Sta-Level" limiter, the FM a "Level Devil". This remained thru the 60's and mid 70's. The AM was better sounding, but was a daytimer only, so switching to the FM side at night was the only way to go. The FM remained mono into the late 1970's when the AM used a Urei BL-40 Modlimiter, and a "Spotmaster" blue-faced compressor was added to the FM.
KDUX-FM went Stereo with a CBS Volumax unit that was a dual channel, but they were "Beautiful Music"
Some of the better sounding AM's used the CBS Audimax and Volumax combination. They were "fat sounding" but were singleband and prone to "holes"
The Best sounding AM was a toss-up between KJR (Lee Hurley) that had a "home-brew" processor, and KITI (Derrek Shannon/ Joe Fiala) who changed the whole audio driver portion of a Wilkenson 1KW transmitter, added a Urei parametric, and the then new Dorrough. The result was a very tight, bright sound.. It was like a FM on the AM dial. Of course, this was way before NSRC.
We got decent AM Stereo from KGHO using an Optimod AM Stereo unit in the 90's but FCC inaction killed it.
 
You would have to get some people like Bob Orban into the conversation to get the real dates and techniques, but my assumption that the first experiments that would develop into what we call "audio processing" today began circa 1960. Where I was living we could get Memphis well and WHBQ had the sound. WMPS was also creating some new sound.

In the back water we were hearing that one of the devices was a box with a screen door spring in the box. A speaker voice coil at one end was exciting the spring to rattle around and at the other end they were using a a phono cartridge or something to pick up the resulting movement and creating that "Top 40 Reverb" sound of the era.

That was the days when stations did proof of performance tests. The consultant who owned the fancy equipment would show up and things would begin to happen after midnight during the "test period". Always plugged into the main announce mic jack. It was commonly believed at the time that adding reverb or equalization to this channel was some kind of violation of FCC rules. The coffee cup chatter was: How are these stations getting away with this! The FCC is gonna' get'cha. And look where we are today.
 
cruiser95fm said:
This guy has a great page with photos of "Old School" processing, including my favorite Gregg Labs

http://www.261.gr/vintage8.html
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One notorious FM processor pictured on his website is the Fairchild Conax:

http://www.261.gr/vintage2.html

Considered the first pre-emphasis limiter, the gain control stage was a not-very-sophisticated clipper in a sealed plug-in module. The "threshold" control on the right side of the front panel was a rotary switch that varied the DC bias voltage on the diodes.

I had one at my high school station, preceded by a homebrew Sta-Level. I recall that we paid $25 for our Conax in 1975, which at that time was all it was really worth. It's hard to believe anyone would consider shelling out nearly $6000 today:

http://soniccircus.com/Fairchild-602-Vintage
 
Thanks for the link. The 8100 (XT2) is the best overall analog box ever built. Their latest digital attempts just don't compare, but man those early boxes STILL sound great today with new caps in them.
 
elchupacabras said:
Thanks for the link. The 8100 (XT2) is the best overall analog box ever built. Their latest digital attempts just don't compare, but man those early boxes STILL sound great today with new caps in them.
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While you're on the topic of "best", I thought I would inject my own opinion.... and it's that if you actually run the latest Orban boxes at the same loudness of an 8100A/1 + XT2.... the new boxes really do blow away the old ones.

One thing that is true to be said is the pre-requisite for screwing up the sound of the new boxes has a much lower threshold today. Don't confuse this with potential. The new boxes have the potential to sound by far superior, and in many implementations - they do.
8)
 
Back to the original question...the earliest stereo generator I remember was tube..a Gates design that was engineered to work with their tube exciter. "Work" being a very relative term. There was considerable improvement in sonic quality at this station when the exciter and stereo generator were replaced with a McMartin and Orban 8000. The processing was a stereo Gates solid state AGC/limiter pair. Circa 1975
 
My first radio job in 1967 was an FM station with a tube type limiter (CCA?) and a bunch of capacitors across the output to minimize the pre-emphasis boost that otherwise required an average modulation level of 20%. That was replaced with an FM Volumax a few months later...huge improvement.
 
Anybody here work the Schulke B/EZ format in the sixties and seventies? I understand he was a freak who would only syndicate music to stations who pledged to NOT process the music in anyway. If ratings were up or down, he would blame it on audio adjustments.
 
Shades of Vladimir Whatsisname - the Mad Russian! "Use the Orban 8000, never let the gain reduction exceed 3dB"
He also felt that Ampex 440s as playbacks picked, and you should use JH-110 MCIs for better sound. On that point, he was right. He was, if mempory serves, the Bonneville guru, and kept them competitive with Shulke.
 
Hi all:

I was a DJ for the Schulke format in the mid 70's. I remember the efforts to keep all the audio clean (like changing out the tape heads at the slightest wear)...yes and very little G/R.

I am interested in learning more about SW processing. Langevin made a unit for SW in the late 1940's that pre-emphasized, clipped and filtered the audio. I am also interested in design techniques of the Optimod 9105A, MBL-100 and others.

73
Dan
W1DAN
 
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