A pot carries a manufacturer number and a date: 137 is CTS, 304 is Stackpole, 140 is Clarostat, 235 is Mallory and 834 is Mel Rain, each followed by a year and a week.
Pots are the easiest codes to find and the weakest evidence in the amp. They are date-coded ahead of use, and a single pot is never enough to date anything.
A pot carries a manufacturer number and a date: 137 is CTS, 304 is Stackpole, 140 is Clarostat, 235 is Mallory and 834 is Mel Rain, each followed by a year and a week.
The problem is timing. Potentiometers and capacitors were often stamped months before they were used, CTS by a month or two, and post-dates of up to 18 months are documented because distributors returned stale batches.
Fender's own history shows the effect: Stackpole pots appear in the 1950s and CTS takes over from 1963, and stock bought under CBS in 1966 and 1967 was still being used in 1973.
The practical rule is that a pot can support a date but never establish one. When a pot disagrees with the tube chart or a transformer, the pot is the witness to doubt.
The code is stamped on the back of the potentiometer case.
Identify the manufacturer number first, then the year and the week.
With a single year digit both decades stay in play until the model or another code decides.
Let it confirm a date established elsewhere rather than deciding one.
whole vintage era · 5 rows · confidence Low · guitarhq — pot & EIA date codes
| Code as marked | Meaning | Source |
|---|---|---|
| 1377918 | 1979, week 18 | Blue Book of Guitar Values — dating tools (PDF) |
| 137-711 | 1947–1957 | Blue Book of Guitar Values — dating tools (PDF) |
| 304-6110 | 1961, week 10 | guitarhq — pot & EIA date codes |
| 137848 | 1948–1958 | guitarhq — pot & EIA date codes |
| 1376623 | 1966, week 23 | Vox Showroom — dating Vox equipment |
| EIA code | Maker | Notes |
|---|---|---|
| 137 | CTS (Chicago Telephone Supply) | |
| 304 | Stackpole | |
| 106 | Allen-Bradley | |
| 134 | CentraLab | |
| 140 | Clarostat | |
| 381 | Bourns Networks | |
| 615 | IRC (International Resistive Company) |
all eras · 1 rows · confidence Low · Les Paul Forum — GA-40 dating thread
Pots and capacitors are often date-coded AHEAD of use (CTS by a month or two; post-dates up to 18 months are documented, distributors returned "stale" batches) — a pot code alone must never be the only witness of a build year (guitarhq). The GA-40 thread is the textbook example: the pot code said 1966 while the amp was a 1956 model — four of five pots agreed, the odd one had been replaced.
| Code as marked | Meaning | Source |
|---|---|---|
| A47-1 MEG Ohm-Z 140 6622 | May 1966 — read as Clarostat (140), 22nd week of 1966 — late May / early June 1966; in that thread this pot was the REPLACED one on a 1956 amp. 'Reported', unofficial. | Les Paul Forum — GA-40 dating thread |
| EIA code | Maker | Notes |
|---|---|---|
| 140 | Clarostat | |
| 137 | CTS | |
| 304 | Stackpole |
all eras · 1 rows · confidence Medium · guitarhq — pot & EIA date codes
Component codes date the PART, not the amp: a replaced transformer/speaker/pot can be newer than the amp. Upper-bound rule — the amp is not older than its newest ORIGINAL component; several independent codes must agree (2+) where no assembly sticker exists. Pots and capacitors are often date-coded AHEAD of use (CTS by a month or two; post-dates up to 18 months are documented, distributors returned "stale" batches) — a pot code alone must never be the only witness of a build year (guitarhq).
| Code as marked | Meaning | Source |
|---|---|---|
| 137 6623 | 1966 — CTS, 23rd week of 1966 — worked example of the format (Vox/CTS example kept here because it is the same EIA system) | Vox Showroom — dating Vox equipment |
| EIA code | Maker | Notes |
|---|---|---|
| 220 | Jensen | |
| 465 | Oxford | |
| 137 | CTS | |
| 328 | Utah | |
| 270 | Quam | |
| 285 | Rola | |
| 391 | Altec/Lansing | |
| 649 | Electro-Voice | |
| 67 | Eminence | |
| 433 | Cleveland | |
| 1098 | Pyle | |
| 117 | Credence | |
| 682 | Electrical Windings | |
| 304 | Stackpole | |
| 235 | Mallory |
CTS, 23rd week of 1966 — and it has to be corroborated, because pots are often stamped ahead of use.
Because pots are made in batches ahead of use and are easy to replace, and the source guidance is not to put too much faith in a pot date.
CTS 137, Stackpole 304, Clarostat 140, Mallory 235 and Mel Rain 834 among them.