ADC HS-4A
Not a product, a part number. The HS-4A survives only as a line in a service manual's component table, and that is the whole of its documented existence.
Overview
The ADC HS-4A is a heatsink. It is not a receiver, a cartridge or an equalizer. It is a piece of thermal hardware with an internal part number, buried in a bill of materials. The available documentation shows a single line item: "HS4A | 141563-1 | HTSK, XLS3 PS." That is the entire record. A reference designator, an internal part number, and a three-word description: heatsink, XLS3, power supply.
The document with that line is a service manual excerpt attributed to Marantz. It is the only source in the available research that names the HS-4A at all, so it gets a close look. The excerpt is a component table, the dense, column-formatted kind technicians used to find parts by reference designator. Every resistor, relay and bracket is cross-referenced to a board location. The HS-4A sits in that table next to three sibling heatsink entries: HS1A and HS2A, both described as "HTSK, XLS3 AMP 202/402," and HS3A, described as "HTSK, XLS3 PS." The pattern is easy to read. These are thermal management parts, grouped by the circuit block they serve. The HS-4A's "PS" suffix puts it in the power supply, the same block as HS3A.
That tells a collector a little, but it is real. The HS-4A is a heatsink, almost certainly an extrusion or stamping sized to dissipate heat from one or more semiconductors in a power supply section. The part number 141563-1 is an internal reference, not a retail model number. The "XLS3" in the description points to a chassis or platform known internally by that name. The same part number 141563-1 appears twice in the excerpt, once for HS3A and once for HS4A. That suggests the two positions share a common heatsink instead of using distinct parts. Whether that means two physically separate heatsinks of identical specification, or one part number reused across two board locations, the table does not say. It does show that the HS-4A was not a one-off component. It was a standardized part drawn from a shared inventory.
When a part number turns up with no product behind it, it is tempting to borrow context from the brand's better-documented lines. ADC built cartridges - the XLM series, the QLM series, the K series - and the Sound Shaper equalizers, and those products have their own pages in this archive. None of that history attaches to the HS-4A. The fact sheet is explicit: no source mentions the HS-4A except the Marantz service manual excerpt, and that excerpt describes it only as a heatsink. There is no evidence it was sold at retail, no evidence it was part of a consumer-facing product, and no evidence it was ever reviewed or measured by the audio press. The magazine review chunks that would normally anchor a page like this are absent. No period publication covered a heatsink.
There is a further wrinkle, and it affects how much weight the one existing document can carry. The excerpt is attributed to Marantz, not to ADC, and the fact sheet notes that no source explicitly attributes the HS-4A to ADC at all. The "XLS3" platform name does not match any ADC product in this archive's published catalog. So the position is layered. The HS-4A appears in a Marantz-attributed service document, in a table that also lists a board marked "XLS2000/XLS2500 AMP/PS," and the archive cannot confirm from available sources that the part was ever an ADC-branded item in the consumer sense. It may be an ADC part used in a platform that carried another brand's name, or it may be a Marantz part misfiled under ADC. The documentation does not settle which.
What remains is a fragment. The HS-4A existed, it carried a part number, and it was specified for the power supply of an XLS3 platform. Whether that platform was a power amplifier, a receiver, a powered speaker, or something else is not documented in any source available here. The fact sheet's recommendation is blunt: additional targeted searching is required, and no guessing should be made. A collector who finds an HS-4A in a parts bin or a service manual margin is looking at internal supply-chain hardware, not a public catalog item.
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