Thread

1. 2b3a51 · 1790540398 · focus · HN ↗

   The tape recorder's manual is available with circuit diagrams [1] and more pictures [2]. I'm not seeing an hf bias oscillator in the circuit unless the manufacturers are being clever. It was half track mono with two speeds, 3.5 ips and 1.875 ips.

   Someone did a lot of work to restore these recordings!

   [1] <a href="https:&#x2F;&#x2F;manualmachine.com&#x2F;concertone&#x2F;tr100&#x2F;8544644-schematic&#x2F;" rel="nofollow">https:&#x2F;&#x2F;manualmachine.com&#x2F;concertone&#x2F;tr100&#x2F;8544644-schematic...

   [2] <a href="https:&#x2F;&#x2F;www.radiomuseum.org&#x2F;r&#x2F;transicord_tr_100.html" rel="nofollow">https:&#x2F;&#x2F;www.radiomuseum.org&#x2F;r&#x2F;transicord_tr_100.html

   1. bsteinbach · 1790561849 · focus · HN ↗

      Indeed, no hf oscillator, instead it looks like it uses DC bias via R12. It&#x27;s also neat to see all the circuitry re-used identically for amplifying the tape in playback, or amplifying the microphone input to record to tape. Was that a standard and obvious plan for the engineers of the time?

      I&#x27;m also curious if R22, the thermistor, would have been just for thermal protection, or if it was actually used to set the operating point for the output transistors in normal operation? Would it have switched on loud and angry before the transistors warmed up and the bias point cooled down, the opposite of a tube amp?

      1. dn3500 · 1790596543 · focus · HN ↗

         I am not familiar with this machine but I owned several other Japanese miniature tape recorders in the 1960s. These germanium transistors are very temperature sensitive, and the thermistor was almost certainly there to compensate for this and keep the bias point steady in normal operation as the temperature varied. And yes a single amplifier was used in all these machines.

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