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 Post subject: Stereo Transmitters
PostPosted: Oct Sun 01, 2017 4:23 pm 
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I am starting a new project. I own a pair of Philco 40-180s and would like to have the ability for them to play stereo.
Here is my idea. A Pilot T601 will be used for an FM tuner. Stereo will be derived from a Magnavox demultiplexer and routed each channel to a separate 6888 transmitter.
Each transmitter will be tuned to a different frequency.
Now I will be able to tune a radio to the left channel and a radio to the right channel
The project will be built on a single chassis.
What do you think? Is this a good approach, or is there a better way of accomplishing this?
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 Post subject: Re: Stereo Transmitters
PostPosted: Oct Sun 01, 2017 4:40 pm 
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While this is a bit of a Rube Goldberg idea**, there is no fundamental reason this would not "work"--meaning that you would get some semblance of stereo sound. One concern might be the phase response of the 2 consoles---if there is a significant difference, I wonder how it would affect stereo imaging.

The obvious answer is to try it.....

**My ultimate Rube Goldberg adventure was the creation of a TV receiver using TWO Tek 545 scopes and a general-purpose VHF receiver. It worked.

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 Post subject: Re: Stereo Transmitters
PostPosted: Oct Sun 01, 2017 7:29 pm 
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Interesting, and agree with pix that you would get a semblance of stereo, but not the real deal. In my radio room, I have Zenith 8S-463 and Philco 40-180 consoles across the room from each other, and occasionally tune them to the same station, or one of my transmitters. Nice "all around" sound, but certainly not stereo.

With true stereo, and listening to a vocal group, the lead singer is often on one channel, and the backup group on the other, IOW, true separation.

Back in the late '50's, my dad had a stereo test record of a Ping-Pong match, and you could hear the ball bounce on one speaker, and then the other.

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 Post subject: Re: Stereo Transmitters
PostPosted: Oct Mon 02, 2017 1:48 am 
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Back in years just preceding stereo FM, there were receivers that could play FM & AM simultaneously... A few stations that had both FM & AM outlets would transmit one channel on FM, the other on AM...


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 Post subject: Re: Stereo Transmitters
PostPosted: Oct Mon 02, 2017 1:55 am 
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unless you really just up for the challenge it would be much easier to just ad a line level input to each radio and send the signal directly to them.

Steve


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 Post subject: Re: Stereo Transmitters
PostPosted: Oct Mon 02, 2017 2:37 am 
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I have one of the tuners from the late 1950s that is intended for AM-FM simulcast stereo. Sometimes I play music from my computer one channel feeding to my AM transmitter and one channel to my FM transmitter so I can simulate the old simulcast broadcasts. Obviously the AM channel doesn't sound as good as the FM channel, but it generally sounds pretty good and I get to recreate a mostly forgotten piece of history. I remember my dad getting the AM radio out of the kitchen and setting it up on the end of the couch, and along with his FM hifi, he would listen to the stereo broadcasts, which if I recall were on for two hours on Sunday evenings.

The OPs idea to broadcast the two stereo channels on two transmitters and two different frequencies should work quite well. As Mark noted, though, he might have to make sure the speakers in the two radios are phased properly. This may be able to be done at the transmitters.

Jeff


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 Post subject: Re: Stereo Transmitters
PostPosted: Oct Mon 02, 2017 3:19 am 
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targeteye wrote:
unless you really just up for the challenge it would be much easier to just ad a line level input to each radio and send the signal directly to them.

Steve

+1

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 Post subject: Re: Stereo Transmitters
PostPosted: Oct Mon 02, 2017 5:40 am 
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There are 2 companies that offer cquam decoder boards the one I have is a meducci and it takes in i.f. and gives out left and right. There are even several transmitters that will give you a cquam signal. Meducci says it won't work on tube sets but I have it working on a heathkit pt1 tuner and an eico hft94 am tuner. In wideband modes these tuners with the transmitted signal I have here is better than f.m. frequency response beats f.m. on theses tuners. It is not too hard to transmit a decent am stereo signal and you can build your own transmitter for it even with tubes. I adapted my 6888 to carry stereo with the stereo exciter and it performs better than expected. Bob Weaver has a 3 tube job that wil do it for you that is not overly complicated.


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 Post subject: Re: Stereo Transmitters
PostPosted: Oct Mon 02, 2017 1:39 pm 
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jeffs01879 wrote:
I have one of the tuners from the late 1950s that is intended for AM-FM simulcast stereo. Sometimes I play music from my computer one channel feeding to my AM transmitter and one channel to my FM transmitter so I can simulate the old simulcast broadcasts. Obviously the AM channel doesn't sound as good as the FM channel, but it generally sounds pretty good and I get to recreate a mostly forgotten piece of history. I remember my dad getting the AM radio out of the kitchen and setting it up on the end of the couch, and along with his FM hifi, he would listen to the stereo broadcasts, which if I recall were on for two hours on Sunday evenings.

The OPs idea to broadcast the two stereo channels on two transmitters and two different frequencies should work quite well. As Mark noted, though, he might have to make sure the speakers in the two radios are phased properly. This may be able to be done at the transmitters.

Jeff

Is your tuner a Madison Fielding?

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 Post subject: Re: Stereo Transmitters
PostPosted: Oct Mon 02, 2017 4:28 pm 
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COM-NAV-ECM wrote:
jeffs01879 wrote:
Is your tuner a Madison Fielding?


No, it's a Pilot 580 from around 1959. Back during the short time that AM-FM simulcast stereo was around, many of the hifi manufacturers offered this type of tuner, including Pilot, Scott, Heathkit, I think Fisher and others. They knew multiplex stereo was coming, my Pilot 580 has two multiplex outputs taken ahead of the de-emphasis network in addition to the normal FM output.

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 Post subject: Re: Stereo Transmitters
PostPosted: Oct Tue 03, 2017 1:14 pm 
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Suggest using an FM tuner with built in MPX decoder.

The Pilot unless it has a jack for connection of an external MPX decoder may not have the necessary IF bandwidth to properly pass the whole FM signal which would mean the MPX decoder will not work properly and will only pass a mono signal.

For the two transmitters I'd suggest setting them 20KHz apart in frequency.

Also add a VU meter to each transmitter set to where over-modulation just starts to occur as the needle moves into the red. That will be very helpful in setting the levels correctly and also ensure you are not over-modulating.

You will then have good stereo sound, although it will be limited to the frequency response of the radios.


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 Post subject: Re: Stereo Transmitters
PostPosted: Oct Tue 03, 2017 8:14 pm 
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Thanks for the feedback, everyone. I am going to go ahead with this project and will post as I go along.

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 Post subject: Re: Stereo Transmitters
PostPosted: Oct Wed 04, 2017 3:55 pm 
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I do recall reading somewhere (maybe on here?) where someone added a MPX out to a Pilot and it worked, so that can be done. I understand that the whole point is to use the two matching radios that you already have, not replace them with an stereo FM tuner. I have done something similar, but using the phono input on an RCA console. I usually just ran mono audio to it, but had my signal tracer sitting right next to the source, on the work bench, and decided to connect one channel to each. While the fidelity of the signal tracer isn't much, I have to admit it was a great improvement over the mono setup. In fact, your idea is great in that you could use any 2 radios in your collection, and rotate them through. Keep us posted on the project.


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 Post subject: Re: Stereo Transmitters
PostPosted: Oct Wed 04, 2017 9:21 pm 
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classicelectronicsguy wrote:
you could use any 2 radios in your collection, and rotate them through.

Exactly!, and have radios in rooms all over the house playing the same thing at the same time. In stereo.

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 Post subject: Re: Stereo Transmitters
PostPosted: Oct Wed 04, 2017 9:48 pm 
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It's still not gonna be true stereo.

Tell me this; if a vocal group recording has the lead singer on the right channel, and the backup group on the left, how would anything short of an FM pilot circuit be able to separate them? Two radios in or out of phase, frequency, etc, might sound like a stereo effect, but that would be the extent of it.

In the above example, both channels would still be combined in each AM receiver.

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 Post subject: Re: Stereo Transmitters
PostPosted: Oct Wed 04, 2017 10:30 pm 
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fifties wrote:
It's still not gonna be true stereo.

Why not? If the left channel is broadcast on one transmitter and the right channel is broadcast on a different frequency on a different transmitter then radios tuned to one transmitter will play the right channel and radios tuned to the other transmitter will play the left channel.
The input could be stereo turntable, tape deck, or FM stereo.

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 Post subject: Re: Stereo Transmitters
PostPosted: Oct Thu 05, 2017 1:37 am 
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kc5gym is correct. If transmitter A is connected to the left channel and transmits at say 1400kHz and transmitter B is connected to the right channel and transmits on say 1600kHz, and radio A is tuned to 1400kHz and radio B is tuned to 1600kHz, each radio receives only one of the two channels and together they provide true stereo.

To me this is not about "high fidelity", it's about using the radios. That's also why I would not add a jack to use the radio only as an audio amplifier, either.

It also should be remembered that when consumer stereo first showed up in the mid to late 1950s, many hifi enthusiasts didn't have the budget (my dad included) to junk their mono systems and buy a new stereo system. They had to cobble together some equipment for the second channel that may or may not have matched their existing equipment, which now was the first channel.

When I want good hifi radio, I have a couple of Dyna FM-3s, and I also have a couple of multiplex adapters I use with the Pilot 580. I have a Heathkit AC-11 and a multiplex adapter that uses a LM4500 IC. But sometimes I want to recreate the FM-AM stereo of the late 1950s. That's when I use the AM and FM transmitters to broadcast simulcast stereo.

Jeff


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 Post subject: Re: Stereo Transmitters
PostPosted: Oct Thu 05, 2017 2:22 am 
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Well as I stated earlier you can do true stereo on am and using any one of the 5 major systems and even some lesser ones and many of them are not that complex or expensive to do. The CQUAM standard on the reciever is easy since the decoder is all on a single chip and not high priced and a transmitter that can create a signal it can decode has been up here on this forum. The modification to the tuner/radio is easy and reversible if you like and you can stagger tune the I.F. and get decent bandwidth aslo reversible.


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 Post subject: Re: Stereo Transmitters
PostPosted: Oct Thu 05, 2017 3:41 am 
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kc5gym wrote:
fifties wrote:
It's still not gonna be true stereo.

Why not? If the left channel is broadcast on one transmitter and the right channel is broadcast on a different frequency on a different transmitter then radios tuned to one transmitter will play the right channel and radios tuned to the other transmitter will play the left channel.
The input could be stereo turntable, tape deck, or FM stereo.

OK, agreed. After diligently re-reading the thread, sounds like a pregnant idea. Please keep us informed on your progress.

BTW, can you elaborate a bit on the Magnavox demultiplexer? Is this a stand alone unit, or part of an FM stereo receiver?

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 Post subject: Re: Stereo Transmitters
PostPosted: Oct Thu 05, 2017 12:31 pm 
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Audioman wrote:
Well as I stated earlier you can do true stereo on am and using any one of the 5 major systems and even some lesser ones and many of them are not that complex or expensive to do. The CQUAM standard on the reciever is easy since the decoder is all on a single chip and not high priced and a transmitter that can create a signal it can decode has been up here on this forum. The modification to the tuner/radio is easy and reversible if you like and you can stagger tune the I.F. and get decent bandwidth aslo reversible.


Yes that can be done if one has an AM stereo radio or Am tuner they want to make stereo, but for an antique radio it would be harder to implement as one would need to add the chip then add a stage of amplification and dedicate two radios to the thing then mod every radio desired to be used with the setup.

The way the OP is doing it is much easier for his intended purpose.


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