TDK LX35-90
An open-reel tape that shows up in the back pages of 1981 audio magazines at $5.39 a reel, and in the calibration tables of Akai decks as a reference formulation.
Overview
The LX35-90 is a 1,800-foot reel of quarter-inch open-reel tape. The market tells you where TDK meant it to sit. Throughout 1981, mail-order dealers advertising in the audio press listed it at $5.39 per reel, with the back-coated LX35-90B at $5.89. Those figures appear repeatedly in Audio (September 1981, p.96) and Audio (December 1981, p.88) dealer listings. That put it well below TDK's own GX35-90B, which the same dealers sold for $7.99 to $8.49 depending on the month, and far under the 3,500-foot LX35-180B at $18.59. It was the workingman's TDK open-reel formulation. Not the flagship, but not the bargain-bin D-series either.
Collectors and tape users care less about the price than about where it sits in the reference tables of the era's decks. The calibration documentation for Akai's GX-series reel-to-reel machines, the GX-77 and GX-747 among them, lists the TDK LX35-90 as a bias-adjust reference point at the "0" position. It sits alongside TDK's SA and GX35-90B formulations as well as Maxell's UD and XLII. In practice, Akai's engineers considered the LX35-90 a known quantity stable enough to calibrate a deck against. Set the bias control to zero, and the machine should be aligned for the LX35-90's sensitivity and high-frequency response. That's a factory service table, not a marketing claim.
The formulation sits in TDK's "LX" family, separate from the "GX" line that commanded the premium. The LX35-90 was the standard, non-back-coated 1,800-foot reel. The LX35-90B added a back coating for improved winding and tape-to-head contact. The two were priced within fifty cents of each other in 1981 dealer listings, which suggests TDK expected most buyers to choose based on their deck's transport rather than budget. Back-coating matters on machines with less sophisticated tension control, because it reduces cinching and improves pack uniformity. It adds nothing to the magnetic formulation itself.
The LX35-90 is most useful for long recording. At 1,800 feet on a standard 7-inch reel, it delivers approximately 48 minutes per side at 7½ ips, or about 96 minutes total for 4-track stereo in both directions. That is the classic "one LP per side" length that made quarter-inch tape the home recordist's medium through the 1970s and into the early '80s. The LX35-180, at 3,500 feet, doubled that for 10½-inch reels, but the 90-minute reel remained the sweet spot for anyone dubbing albums or assembling compilation tapes. TDK's own catalog treated the 35-90 length as the volume seller. Dealer ads list it first among the LX reels, with the 180-foot variant as the premium option.
The LX formulation was designed for the normal-bias, high-output end of the market, the kind of tape a mid-line Akai or Teac could bias correctly without a struggle. The Akai calibration tables place it at the same bias setting as Maxell UD and TDK SA. So it behaves predictably on decks calibrated for the common Japanese formulations of the period. The LX35-90 was built to be the tape you could afford to use every day, not the one you saved for the master.
A note on the format for anyone new to open reel. Quarter-inch tape on a 7-inch plastic reel was the universal home format from the late 1950s through the mid-1980s. It remains the most serviceable vintage medium: the reels are standardized, the formulations are well-documented, and a working deck can still be brought back to spec. The LX35-90's 1,800-foot length is the most common reel size in the format, so replacement reels and empty take-ups are easy to source. That is a large part of why LX35-90 reels still turn up in estate lots and dealer inventories four decades after they were manufactured.
Collectibility for open-reel tape is odd. Sealed NOS reels of desirable formulations command real money, but the market is narrow and the buyers are working recordists rather than display collectors. The LX35-90 sits in the middle: not rare enough to be a trophy, not cheap enough to be disposable. A sealed reel is worth having if the formulation suits your deck's bias. An opened reel is worth having if the tape has been stored well and shows no signs of binder breakdown. The back-coated LX35-90B is the more desirable of the two for archival work, since the coating helps with winding stability and reduces print-through on long storage.
The LX35-90 has no cult following and no legendary status. It was a competent, affordable, well-calibrated tape that did its job on tens of thousands of home decks. The reference tables in Akai's service manuals are the best evidence that a major deck manufacturer trusted TDK's mid-line formulation enough to use it as a calibration standard. It sold for five dollars and change in 1981.
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