TDK ADX-90
The record on the ADX-90 is thin. No manufacturer documentation for this exact tape has surfaced, and what we know comes almost entirely from mail-order listings in the audio press of the early-to-mid 1980s. Those listings settle one thing: the ADX-90 was a real, sold, catalog-listed TDK cassette, priced between the company's SA line and its premium metals.
Tape World, a Butler, PA mail-order house, listed the ADX-90 at $3.19 in December 1982, dropped it to $2.99 by late 1983, and had it at $2.79 by January 1984. It always sat just above the SA-90 and well below the SAX-90 and MA-90. Other sellers tracked it too. Quality Tapes in Brooklyn quoted $2.55 in January 1984, and a Leopold's holiday flyer that same season listed it at $3.79 against a $2.79 SA-90. That steady price gap shows where TDK positioned it - a step-up ferric-type tape, not a budget D-series and not a metal.
What the ADX formulation actually was, how long it was made, and what its bias/equalization requirements were are not documented in anything we've found. The "AD" in the name points to TDK's Acoustic Dynamic ferric line, the same family as the AD-90 and AD-60 that appear alongside it in these ads. The "X" suggests an upgraded variant. That's inference from the naming, not a spec sheet, and we won't state it as fact. The only period image reference we have is a 1982 TDK Acoustic Dynamic cassette advertisement, which shows the family but not this specific model's packaging.
So the ADX-90 was a genuine TDK cassette, actively sold at retail in the U.S. between at least 1982 and 1984, priced as a mid-premium ferric. The archive is still waiting for a box, a spec sheet, or a review to turn up.
- Type: Cassette tape, TDK "AD"-family ferric (inferred from naming only; not documented)
- Length: Unknown (the -90 designation is not documented as a length in any source)
- Observed street prices: ~$2.55–$3.79, 1982–1984, U.S. mail order
- Positioning: Above SA-90, below SAX-90 and MA-90 in the TDK lineup
- Production years: Unknown; documented on sale 1982–1984
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