multiplex

I'm working on a Sansui 5500 receiver and am having an issue with the FM Multiplex board. I get good FM reception but no stereo. I have a good 19 kHz, 3 Vrms signal after TR402 and a 38 kHz, 1Vrms signal at the base of TR403 but no 38 kHz on the collector of TR403. DC voltages around the...

Working on my Sansui 250 tube receiver that I’ve been listening to for a while now. Did a full recap and it sounds great but the multiplex never worked. I swapped it out today and decided to take a look at it and found 0v on pin 6 of the 6aq8. Turns out the primary coil of T7 is open. It’s the...

Working on a Sansui 1000 (not 1000a) tube receiver. When in multiplex mode one channel is muffled and slightly lower than the other. I’ve traced it to the 12au7 tube I’m assuming that splits the stereo signal. I swap the inputs to the grids and it does not swap channels. I swap the outputs at...

Hello, I am close to finish restoring a QR-6500 (serial is 211091683 if this can help with differences / mods). I need to verify the position of a strap (see picture below) on the solder side of the F-1322 decoder board. The service manual seems to have the right schematic (at least something...

Hi gang, What be the purpose of the shorting bar in this Motorola tuner diagram, and when is it necessary to move it to the Mono or Stereo position? Does it come into play when using a multiplex adapter for FM stereo? Ignorantly yours, JP

Hi Folks, Gotta MX-110 on the bench here (Ser. 188Z6) with a unique issue I have not encountered before. Problem: All (including FM Mono) works awesome. MPX position delivers a mono L-R (left minus right, the info contained on the 38KHz DSB subcarrier) to the speakers. There appears to have no...

Just finished recapping a lovely little SX-626, and the FM board doesn't want to go stereo. The Muting switch sometimes works, sometimes cancels all strong signals and goes silent. The Stereo light flickers while tuning, sometimes indicates stereo on weaker stations, but often does not glow on...

Pleased to be making progress on a Fisher 800C that was gifted to me in pretty sad shape. The Fisher 400 and 500C (same as the 800C but without an AM section) were our standard bench receivers when I was running service operations for Pacific Stereo in the 70s because they were so reliable. I'm...