Dating an amplifier by its component codes

Most amplifiers cannot be dated from a serial number, and the ones that can are the minority. What nearly all of them carry instead is a source-date code stamped on the pots, the transformers and the speaker — who made the part, and the week they made it. This reads that code and shows every year it could be, which for the older ones is more than one.

It dates the part, not the amplifier. That sentence is the whole tool. A pot sat in a bin before it was fitted, so its code gives you the earliest the amp can possibly be — never the date it was built.

What the code is, and what it is not

The Electronic Industries Association gave each American component manufacturer a number. Stamped on the part, that number is followed by the date it was made — so 137 6224 is CTS, 1962, week 24.

Three things follow from that, and the third is the one people get wrong.

This page treats that gap as the answer rather than a footnote, because the gap is where people lose money. An amplifier advertised as a 1962 on the strength of a 1962 pot may be a 1963 or a 1964 that was built from older stock, and it may be a 1970s amp with a pot somebody replaced.

Where to find the code

On a pot, it is stamped or inked into the metal casing — you have to look at the side or the back, which usually means taking the chassis out. On a speaker it is on the frame or the magnet. On a transformer it is on the bell end or the lamination stack.

Codes are often separated by a space, a hyphen or a full stop, and they are frequently worn, painted over or hidden under solder. Type what you can read and this page will tell you which readings fit rather than insisting on one format.

Where this comes from

The structure of the code — a maker number, then a year, then a week — is an EIA standard and is described consistently in several places. This page took it from two independent ones and they disagree about one thing, which is recorded above rather than smoothed over: whether a single-digit year code can be later than the 1950s.

The handful of manufacturer numbers this page does recognise — CTS, Centralab, Stackpole, Allen-Bradley, Clarostat, Bourns — are the common ones, and they appear identically across every source consulted. The several hundred others are somebody's compilation and are linked rather than lifted.

Or start from the maker

The codes above work on almost any amplifier. A few makers also put a date in the serial number — and rather more put one somewhere else entirely, or say plainly that it cannot be done. Twenty-seven have been looked at so far.

Looked at, and nothing usable was found

These sixty-four have been researched. Not one of them publishes a way to date an amplifier, and saying so is the useful part — “nobody has looked” and “somebody looked and came back empty” are different answers, and only one of them means it is worth you looking again.

They are grouped by why, because the reasons are not interchangeable, and the group is usually more useful than the row.

One family, many badges

Valco built amplifiers under several names at once, exactly as they did guitars. The guitar page explains at length why their ranges are not reproduced on this site: Valco’s own records do not survive, and what exists is research published in a book.

A sideline from a guitar maker

All of these are on this site’s guitar page, and a guitar scheme does not carry across to an amplifier. Different factory, different numbering, often a different decade. Nothing was found that dates the amplifiers, and the component codes above are the route.

A small shop, where there was never a system

A production numbering scheme is the wrong thing to look for in a workshop that builds a few dozen amplifiers a year. Nearly all of these will answer an email, and most keep a book. Where a date exists it is usually written inside by the person who built it, which is worth more than any table.

A modelling box, where the question is usually different

For these the useful question is rarely the year. It is which hardware revision and which firmware, and the makers publish that. None of them is old enough to have a vintage market that turns on a date, and none publishes a date scheme.

Everything else looked at

No maker statement and nothing citable found. In each case the component codes at the top of this page are the route.

If you know better for any of these — particularly a maker who publishes something this missed — please say so. A single link would move one of them out of this section, and that is the most useful correction anyone could send.

All ninety-three have been looked at

There is nothing waiting here. The list came from Wikipedia’s categories, the same way the guitar page’s did, and every name on it has been through this process. Twenty-nine have an entry above; sixty-four were researched and came back with nothing usable.

Three makers out of ninety-three publish a way to date their own amplifiers — Ampeg, Matchless and Dr. Z. One more, Fender, publishes one this site cannot reach. That is the honest headline, and it is why the component codes are at the top of this page rather than the bottom: for almost every amplifier ever built, the parts are the answer.

As with the guitar page, finished describes a list rather than the world. If your amplifier is from a maker who was never on it, telling us the name is the most useful thing you could do.