Any info on a Trio AF-220 tuner?

[Hewie]

I fell into a Trio AF-220 tuner and am having troubles finding any info, can anybody help me? I contacted Kenwood, but they don't have anything in their archives, and searches on the net don't lead to anything. Anyone know where to track down a schematic for this or something similar. The tubes are as follows: 2 x 12AT7, 4 x 6BA6, 1 x 6BE6, 1 x 6AU6, 1 x 6AL5, 1 x 6X4.
There are 5 outputs and they have me stumped as well labeled as follow: (0 = OUTPUT)


AM.FM.MX_____AM.MX________FM
____0____________0____________0________0______0
Monaural_______Right__________LEFT______MX ADAPTER

Did these units have real stereo as well as multipled stereo? And why did they do that?


One channel has low output and a heavy buzz, so I plan on trying to trouble shoot it, but is it worth it for this unit or does it belong in the parts bin?

Thanks for any insight.
Dave

 

[Tom Bavis]

These earlier ones often needed a separate multiplex adapter if you wanted stereo. Sounds like the case here. Left channel may not connect to anything without it. Use it for mono, or (good luck) look for a multiplex adapter. Most any brand would work, even a solid state one.

 

[EC8010]

GE/Zenith

The MPX outputs will be before de-emphasis. You need a GE/Zenith stereo decoder. FM stereo is transmitted by sending L+R as the mono signal and sending L-R on a Double SideBand Suppressed Carrier (amplitude modulation) at 38kHz. A 19kHz pilot tone is transmitted which is used to regenerate the carrier required for demodulation of the DSBSC. Once L-R have been recovered, they can be matrixed with L+R to produce L and R individually, and finally have de-emphasis applied.

There used to be all manner of chips available to do this (MC1310 was an early one). Fixing your hum problem is probably just a matter of replacing dried-out power supply electrolytics. Decoders are commonly available in the UK for retro-fitting to Leak Troughline tuners that had indifferent decoders.