Concern with classic Marantz receiver

[rivieraranch]

I bought a Marantz 2218 receiver to furnish 2-channel amplification to the television audio signal and for FM in my living room. The unit is in mint condition, silver face & dial, all the lights work; the tuner is great; the only thing that concerns me is that the red "STEREO" indicator light only lights up in FM STEREO mode. In the other modes it does not light up,it glows a little bit, probably backlit by the adjacent bulbs. Does this mean that it is not putting out a stereo signal from the other outs?

[stormin]

I believe the 2218 was designed that way. Others with more experience with that particular model may chime in with their knowledge.

Let me direct you to a great site for vintage audio gear.

http://audiokarma.org/

All of your questions concerning your marantz can be answered there.

[ZAKO]

The red light is to indicate the FM stereo Multiplex is picking up a stereo program from the broadcast station.

[rivieraranch]

The unit does not have a mono switch; the selector switch has FM mono or FM stereo.

[Soundthought]

[WMcD]

This sounds correct.

I'm old enough to give history lessons here . . . should you care to read.

My recall is that the "stereo" standard was not established in the earliest days of FM broadcasting. The earliest stations were mono. The channels though were wide enough to support bandwidth for more channels. Like HDTV, it was a matter that there were no or few stereo recordings, thus nothing to transmit. Hence no transmitters, and hence no receivers.

Some of the earliest efforts at broadcast used an AM and FM station owned by the same company.

At some point there were proposals to the FCC for the various technical schemes to allow multichannel audio out of one FM channel. I recall an article in Audio that one writer had a scheme to squeeze in very many channels and thought he was going to be the winner. However, the one that was accepted allowed for only three channels.

The third channel was the SCA (subsidiary audio?) channel which was sometimes used for Musak and the like. A private commercial free channel. I don't know the extent to which this is used today.

The otherwise "stereo" scheme was clever and of course is still used today. It had be compatable with the existing mono scheme. The mono signal is Left plus Right.

But the second channel transmitted is Left minus Right.

In the working "stereo" receiver the two raw channels are:

1) Summed. So L+R plus L-R = L.

2) Subtracted. So L+R - L-R = R.

Please note this means that FM stereo coming out of the transmitter is not raw L and R at all.

There is a problem with getting the second channel to decode properly. You need a signal to use as a phase reference. That, I recall, after doubling?, is the 38 kHz "pilot tone".

Of course normal receivers did not have any such circuitry to detect and decode the pilot tone and the extra channel. In the early situations a receiver would have a "MPX" (multiplex) output. You had to buy an outboard decoder. You may see the output on some vintage receivers.

There was another problem. If the stereo set up (outboard or not) listened to a mono broadcast, there was a noise issue. The solution was to have circuitry to listen for the pilot tone. When present, it would light up the 'stereo' light. People would know when to switch on or off the decoding circuit. The presense of the pilot tone signaled the presences of the second channel and "stereo."

Over the years the switch became automatic. Now it is a bit redundant in that very few broadcast mono FM.

It is my guess that your circuitry is set up so that the pilot tone decoder (light up the lamp) is only enabled when you switch to FM stereo. The above descibes why that came to be.

It would have been a good marketing ploy to have mono receivers with a pilot tone detector. It would entice the owner with the possiblity of stereo should they want to purchase an outboard decoder. Then you need the second amp, the second speaker, etc. Just like HT today!

Best,

Gil

[Duke Spinner]

don't forget to fus eyour Speaker s....

[Duke Spinner]

Whoop 's ..

try

"fuse your speakers"