Sometimes there just isn't enough information on electric instruments and amps to allow them to be properely dated. And many people ask me to try and determine the year of their old amplifier, or to help them with the year of their older off-brand electric guitar.
Since I primarily collect amps by Fender, and guitars by Gibson, Fender, Martin, National, Epiphone, Gretsch and Rickenbacker, I really can't help them with these other less popular brands. As you have probably noticed, there is plenty of information here to help date the brands that I am interested in. But where does that leave everyone else?
Well I'm not one to leave you out in the (informational) cold, so here's something that I use quite often in dating amplifiers and electric guitars. It's called the "source-date code", and it can help determine the approximate age of an electric instrument by the date its components were manufactured.
Source-Date Codes : On American made vintage gear, the pots and speakers provide an excellent opportunity to date a piece of equipment by referencing their "source-date code".
The source-date code found on pots and speakers gives the manufacturer and date (roughly) when the components were made. It may have been some time before the part was installed at the factory, but it still provides a good approximation of when the gear was made. This is especially helpful on (less popular) gear that doesn`t have reliable serial#`s or other information to date them.
The source-date code will signify the earliest possible date that the instrument or amp could have been made. This isn't going to be exact, but it will give you a "ball-park" age. And remember, even the dates indicated by the pots aren't that exact. For example, if you buy a brand new CTS pot today, they are dated a month or two in advance! I don't know the reason for this, but it's worth mentioning.
The source-date codes are under the framework of the "Electronic Industries Association", which is a non-profit organization representing the manufacturers of electronic parts. The EIA source-date code is a numeric code, assigned and registered by the EIA. It can be stamped or marked on any product to identify the production source (vendor) and date of manufacturer. Source-date codes have been published by the EIA since 1924. The EIA can be contacted via mail: Electronics Industries Association, 2001 Pennsylvania Ave NW, Washington, D.C. 20006.
Consideration and exceptions : Source-date codes weren't an industry standard until after WWII. But I have seen them used on Stackpole pots on electric National guitars as early as 1935. The first time date-source codes were published was 1924, so I guess you could see them as early as the late 1920's.
Most Fenders from 1966 to 1969 have 1966 dated CTS pots. Apparently CBS/Fender bought a large stock of pots in 1966 that lasted till 1969.
On popular Fender models, the pot date can be very close to the actual date of the instrument. On less popular Fender instruments, such as LapSteels, pots can be as much as two years earlier than the actual date of the instrument. Gibson didn't start using pots with source-date codes till 1953 or 1954.
Originality : Of course this all assumes the pot or speaker is original. You have to make that call. I would suggest checking the solder joints - are they clean? Are the wires of the right era (cloth insulation for older stuff)? If so, you can check the pot or speaker for the source-date code, and determine an approximate age from that.
How the Source-Date Code Works. The source-date code on a pot is a 6 or 7 digit code impressed into the casing of the potentiometer. For speakers this code can be 5, 6, 7 or 8 digits long, and it's ink-stamped or paint-stamped on the "bell housing" of the speaker.
In either case, the code works the same. The first 3 digits on a pot, or the first 2, 3 or 4 digits on a speaker are the source or manufacturer code.
The remaining 3 or 4 digits are the date code. In 3 digit dates code, the 1st digit is the last digit of the year. On 4 digits date codes, the 1st and 2nd digits are the last two digits of the year. In either case, the remaining 2 digits are the week of manufacture (01 to 52). With this in mind, remember if the last two digits of the source-date code are greater than 52, you're not looking at the source-date code!
Also it's worth mentioning:
Sometimes there is a space or hyphen between the manufacturer code and the year/week code.
3 digit date codes were used in the 1940's and 1950's.
4 digit date codes were used in the 1960's and later (this makes determining the year much simplier!).
On 3 digit date codes, you have to "guess" the decade of the pot or speaker. Usually this isn't too difficult.
Pots used by Fender. The middle one is a CTS pot (Chicago Telephone Supply, manufacturer #137) from the 30th week of 1966. The pots on the left and right are Stackpole pots (manufacture #304). Note the different position of the markings, even on pots from the same maker.
Left: The source-date code (285709) on a speaker. In this case, the speaker is made by Rola (285) in the 9th week of 1957 (709). The decade, though not directly shown by the source-date code, was easily determined because this particular amp was only made during the 1950s. Note the font style of the source-date code number always seems to be the same, for all speaker manufacturers.
Right: Same thing here. Jensen (220) speaker made in the 41st week of 1959 (941).
Pot Source Codes. Here are the most common pot manufacturers (the first 3 digits of the source-date code):
106 = Allen-Bradley
134 = CentraLab
137 = CTS (Chicago Telephone Supply, pots and speakers)
140 = Clarostat
304 = Stackpole
381 = Bourns Networks
615 = IRC (International Resistive Company) - see below
Fender Products. During the 1950's, Fender used mostly Stackpole (#304) pots. Then in roughly early 1963, they changed to CTS (#137) pots. In 1967 (after CBS bought Fender), Fender bought a HUGE supply of pots from CTS. This supply lasted for over five years. So guitars and amps made as late as 1973 can still have 1967 date codes from this huge 1967 stocking.
All during Fender's life as an amplifier maker, then used speakers made by Jensen (#220), CTS (#137), Oxford (#465), Utah (#328) and Altec-Lansing (#391). Till about 1961, Jensen was the only Fender speaker supplier. Then from 1962 and later you see Fender using speakers from all the above mentioned makers.
National, Valco, Supro Amplifier Products. Note the use of "550" as a source code on these products. Actually, it's not a source code but is a manufacturers code for all National, Valco, Supro products. Found as second stamping on speakers as a date code 550XXX from 1947 through the 50's and 60's (all the 1940's amps are generally field coil Rola spkrs).
Manufacturer Source Codes. Below are many manufacturer source codes (which are the first 2,3, or 4 digits of the source-date code).
Common Guitar Speaker Manufacturers:
67 = Eminence
137 = CTS (Chicago Telephone Supply)
220 = Jenson
285 = Rola
308 = Stromberg-Carlson
328 = Utah
336 = Western Electric
391 = Altec-Lansing
416 = Heath
465 = Oxford
589 = Bogen
649 = Electro-Voice
Some tidbits on Jensen : Fender used Jensen speakers until 1972 when all Jensen production (and one engineer) was switched to The Rola Company in Cleveland OH (Rola was a division of Jensen). Prior to the re-structuring of Jensen in '71-'72, Jensen quality had suffered terribly. When Rola started to make speaker for Jensen in 1972, Rola initially used the Jensen 220 manufacturer code, but by the end of 1972 changed to the 285 Rola code. Regaining OEM customer confidence after the Jensen years was a long process due to the Rola-Jensen ties.
Other Speaker Manufacturers :
24 = Becker
101 = Admiral
106 = Allen-Bradley
119 = Automatic mfg.
125 = Bendix
130 = Panasonic
132 = Talk-a-Phone
145 = Consolidated
150 = Crecent
169 = Hitachi
185 = Motorola
188 = General Electric
213 = Dearborn Wire
230 = Littlefuse
232 = Magnavox
235 = Mallory - North American Capacitor
244 = Muter
245 = National
251 = Ohmite
252 = Dukane
258 = Perm-O-Flux
260 = Philco
270 = Quam-Nichols
274 = RCA
277 = Emerson
280 = Raytheon
300 = Speer
381 = Bourns
285 = Rola
286 = Ross
296 = Solar
312 = Sylania
336 = Western Electric
343 = Zenith
371 = Best
374 = Cletron
394 = Foster Transformer
423 = North American Philips (Norelco)
433 = Cleveland
449 = Wilder
466 = Delco
532 = Ward Leonard
549 = Midwest
555 = Waldom Electronics
575 = Heppner
649 = Electro-Voice
706 = Pioneer
719 = Carbonneau
722 = Milwaukee Resistor
742 = Esquire
748 = Russell
756 = Universal
767 = Quincy
787 = Sonatone
789 = McGregor
794 = Harmon Kardon
795 = Atlas
816 = Dale
828 = Midland
840 = Ampex
847 = University
918 = Oaktron
932 = Atlas
1056 = Fisher
1059 = Channel
1098 = Pyle
1113 = Acoustic Fiber Sound
1149 = Curtis Mathes
1191 = Micro Magnet
Tubes/Transistors Codes :
111 = Amperex (USA)
125 = Bendix
158 = DuMont
185 = Motorola
188 = General Electric Co (USA)
210 = Hytron (CBS-Hytron)
260 = Philco
274 = RCA (Radio Corp of America)
280 = Raytheon
312 = Sylvania (Hygrade Sylvania Corp)
322 = Tung-Sol
366 = Western Electric
337 = Westinghouse
343 = Zenith Radio Corp (CRT's)
466 = Delco
980 = Texas Instruments
Capacitor Codes :
102 = Aerovox Corp
109 = American Condensor
134 = Centralab
135 = Chicago Condensor
163 = Aerovox Hi-Q Division
178 = John E Fast
188 = General Electric
235 = Mallory
240 = Micamold
242 = Millen
273 = Radio Condensor Company
296 = Solar
303 = Sprague (every Gibson lover's favorite!)
438 = Gudeman
446 = Good-All
461 = Barker & Wiiliamson
472 = Pyramid
516 = United Condensor
569 = Electrical Utilities Corp
616 = Illinois Capacitor (Condensor)
648 = American Radionic
658 = Sangamo
705 = Ajax
710 = Standard Condensor
732 = RMC (Radio Materials Corp)
885 = Condensor Manufacturers
Transformers & Coil Codes :
138 = Stancor (Chicago-Standard)
141 = Coil Engineering
172 = Ensign Coil
183 = Freed
194 = General Radio
218 = Jefferson Electric
238 = Thordarsen-Meissner
239 = Merit Coil & Transformer
305 = Standard Coil
352 = Essex (Transformer Division)
366 = New York Transformer
391 = Altec Lansing-Peerless
394 = Foster Transformer
412 = General Transformer
418 = United Transformer Corp (UTC)
489 = Radio-Television Products Corp
452 = Empire Coil
503 = Caledonia
524 = Triwec Transformer
549 = Midwest Coil & Transformer
550 = Standard Winding Co
572 = F & V Coil Winding
606 = Woodward-Schumacher
637 = Central Coil
682 = Electrical Windings
757 = Grand Transformers
773 = Forest Electric
776 = Ogden Coil & Transformer
830 = Triad
831 = Better Coil & Transformer
843 = Klipsch
878 = Acro Products (Acrosound)
883 = Mohawk
892 = American Transformer
897 = Tresco
906 = Coilcraft
908 = Aerocoil
928 = Acme Coil & Transformer
933 = Magnetic Coil Mfring
934 = Oaktron
1005 = Northlake
1052 = Pacific
Other Manufacturers :
139 = Cinch (Sockets, connectors)
152 = Crosley (Radios)
194 = General Radio (Test Equip)
199 = Hallicrafters (Ham & SW gear)
222 = E F Johnson (Sockets, ham xcvrs)
248 = Arvin (Sears radios & TVs)
254 = Packard Bell (TVs radios computers)
260 = Philco (Radios & TVs)
262 = Philmore (Hardware)
277 = Emerson (Radios & TVs)
343 = Zenith (Radios & TVs)
416 = Heath (Electronic kits)
772 = Muntz (Cheap TVs)
787 = Sonotone (Phono cartridges)
Examples of Source-Date Codes. With all this information in mind, can you identify the following manufacturer and date of these source-date codes?
220 7001 : Jensen speaker, 1st week of 1970.
137341 : CTS, 41st week of 1953 (or 1943 or 1963, but probably 1953 as source-date codes weren't used much during or before WWII, and 4 digit date codes weren't used till the 1960's and later).
304-6110 : Stackpole pot, 10th week of 1961.
137848 : CTS, 48th week or 1948 or 1958.
4656755 : Not a source-date code. Can you see why? If you can't, read the above information again!
Here's another example : 304809
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