Sony TC-9520

Sony’s TC-9520 is a mid-1970s 4‑channel open‑reel deck that is mechanically based on the TC‑9540 “discrete 4‑channel” model but limited to 2‑channel record/playback in normal use. It is essentially a quad-capable transport and headblock repurposed as a high-grade stereo deck with access to 4‑track playback functionality.

• It’s described as a “4-channel tape deck with 2-channel recording/playback capability.” That means it uses a tape transport derived from Sony’s higher-end models — but unlike its sibling model (Sony TC-9540), the TC-9520 does not support 4-channel recording — it only records in 2-channel (stereo) mode. 

• The underlying transport/mechanism is reportedly based on professional-grade designs (for example, from the “TC-707 series” lineage), giving it more stable and accurate tape handling than very basic consumer decks. 

• The control logic was somewhat advanced for its time: the “system control mechanism” allowed button presses at almost any time — e.g. you could hit Play while the deck was fast-forwarding or rewinding. audio-database.com

In short: the TC-9520 occupies a middle ground — more robust and better-engineered than entry-level domestic reel decks, yet not a full 4-channel/multitrack recorder.

Because the TC-9520 shares its mechanical basis with the TC-9540, which is more documented, we can infer certain traits likely carried over. 

• Tape transport & mechanism: stable, precision-type chassis inherited from Sony’s higher-end reel decks — indicating reliable tape tension/stability and professional-grade reliability. 

• Format: ¼-inch open-reel tape (standard), 2-channel (stereo) record/playback. 

• Controls & usability: you get flexible control (start, stop, ffwd, rewind, play) with system logic that tolerates operations like play-while-rewind aiming to reduce mechanical stress or avoid “click” noise common in lower-end 3-motor decks.