TDK HD-11 Head Demagnetizer
A pocket-sized wand rated at 640 gauss, sold for $34.99, that TDK tucked into the fine print of its open-reel ads - and that every serious tape operator eventually needed.
Overview
The HD-11 is a hand-held, battery-operated tape head demagnetizer. It's the kind of accessory that never gets a catalog cover but decides whether a deck sounds like itself or like a deck with a magnetized head. TDK rated the field strength at 640 gauss and priced it at $34.99, according to Modern Recording (April 1981, p.29), which listed it for use on both cassette and open-reel decks. The rating is the whole point. It's enough to flush residual magnetism out of a head's core, and not so much that a careless operator waves it around the transport and makes things worse.
The tip is what separates the HD-11 from a bar magnet on a stick. TDK fitted it with plastic-covered pivoting pole pieces, and Modern Recording (April 1981, p.29) noted that this design facilitates access to tape heads. The pivot lets the probe reach the awkward corners of a transport. That means the heads, but also the guides and support structure around them, which can carry residual magnetism of their own.
The caution is not boilerplate. TDK's own instructions emphasized that the job "requires close attention," and owners who have done it wrong once tend not to do it wrong twice. Battery operation helps here: no line cord snaking across the bench, no grounding questions, just a self-contained tool you switch on, bring slowly toward the head, and withdraw slowly away. Collectors who service their own open-reel machines tend to keep one in the drawer next to the cotton swabs and the HC-1 cleaner, because the sequence TDK recommended - demagnetize, then clean, then inspect - starts with this device.
The HD-11 is not a cleaner. That job belonged to TDK's HC-1, a cassette-configuration cleaner the company recommended after every eight hours of play. It is also not the cassette-deck-specific HD-01, which slots into a transport like an ordinary cassette and addresses the heads, guides, and support structure in one pass. The HD-11 is the generalist: a hand-held wand for cassette decks and open-reel recorders alike, sold as an accessory to TDK's tape line and promoted in the same breath as the GX and LX open-reel tapes. In TDK's 1981-82 magazine advertising for those tapes, the demagnetizer appears almost as a postscript - "to keep our perfect tape perfect, use the TDK HD-11 Head Demagnetizer" - which puts it low in the product hierarchy: small, cheap, and assumed.
It was never a prestige item, so it was never babied. Plenty were bought, used for a decade, and left in a box. The 640-gauss rating and the pivoting plastic tip are both documented in the period press. Production years, battery type, and the specifics of the internal coil were not published in the sources available here, and the archive will not guess at them. The HD-11 was on the market by early 1981, was still being recommended in TDK's maintenance copy as late as mid-1985, and sold at $34.99.
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