Stromberg-Carlson No. 20

A catalog number that turns up in three different documents and means something different in every one of them.

Overview

The Stromberg-Carlson No. 20 is one of those designations that collectors learn to handle with tongs, because the number shows up attached to more than one thing across the surviving Stromberg-Carlson paperwork. In a 1922-era catalog and sale sheet, "No. 20" appears in the catalog-number column alongside a "No. 20 Variometer assembled complete," listed at a regular price of $4.50 and marked down to $2.95 in the clearance table. That same table also carries a "No. 18 Variometer assembled complete" at the identical $4.50 regular and $2.95 sale figure, which is worth noting because it tells you the two numbers sat side by side in the same parts list rather than describing the same object under two names.

A later document — a 1928-era dealer sheet for the Sargent-Rayment Station Isolator — mentions "Stromberg-Carlson No. 734" in a list of receivers the Model A isolator was built to serve. The No. 20 does not appear in that list, but the sheet is useful context: it shows how Stromberg-Carlson model numbers were being cited by third-party accessory makers in the late 1920s. Whether the No. 20 designation belongs to the variometer of the early 1920s or to something else entirely is not settled by the documents available.

What can be said with confidence is narrow. The No. 20 appears in at least one early Stromberg-Carlson parts catalog as a variometer — a variable inductance tuning component used in the regenerative and tuned-radio-frequency receivers of the 1920s — and it carried a list price of $4.50 before being discounted to $2.95 in a stock-reduction sale. The sale sheet frames the markdowns as a way "to reduce stock," and the items are offered "for cash" and "subject to prior sale," which is standard clearance language of the period. The No. 20 sat in a table that also included crystal detectors, rheostats, dials and knobs, grid condensers, flat-plate condensers, switch levers and stops, binding posts, tuning coils, and a range of headphones from Leich, Kellogg, and Holzer-Cabot. In other words, the No. 20 was one line item in a broader catalog of radio parts aimed at the home constructor and the service trade, not a flagship product with its own dedicated documentation.

The third document that uses the "No. 20" label is a set-analyzer article from the early 1930s, but there the number refers to a switch position on a test instrument — "No. 20 is 'P6-K30V,' meaning the voltmeter is between the 'pentode grid' and cathode of an R.F. pentode tube" — and has nothing to do with Stromberg-Carlson. That is the kind of coincidence that trips up casual research, and it is worth flagging plainly: the No. 20 designation is not unique to Stromberg-Carlson, and a search for the term will surface unrelated hits. The fourth document, a piece on auto-radio noise elimination, mentions "No. 20 wires" in a discussion of voltage drop along unshielded conductors, which is likewise unrelated.

So the honest summary is that the Stromberg-Carlson No. 20 is documented as a variometer in an early parts catalog, priced at $4.50 and cleared at $2.95, and essentially nothing else about it is confirmed. The fact sheet for this model is empty by design — the research returned nothing beyond what the catalog and dealer documents happen to mention — and that emptiness is itself the most important thing to communicate. A page that invents specifications for a 1920s variometer would be worse than useless; it would be actively misleading to the restorers and historians who rely on this archive.

What a variometer does, for readers who have not handled one, is provide continuously variable inductance in a tuned circuit. The 1920s receiver builder used them to tune across a band without swapping coils, and the quality of a variometer — its winding, its rotor contact, its mechanical stability — had a direct effect on how selectively and how stably a set would tune. Whether the No. 20 variometer lived up to it is not something the surviving documents address.

Collectors looking for a No. 20 today should expect to find it, if at all, as an unlabeled or partially labeled component in a box of early radio parts, not as an identified piece with provenance. Contemporary coverage of the era's recorded repertoire, such as a survey of virtuoso transcriptions in High-Fidelity (October 1958, p.116), offers no mention of the No. 20. The $4.50 list price and $2.95 sale price are the only hard numbers attached to the model in any document this archive has located. Everything else — the year of introduction, the year of discontinuation, the physical dimensions, the inductance range, the materials — remains unknown. Anyone who turns up a documented example with original packaging or a dated invoice would be adding genuinely new information to the record, and this archive would welcome it.