ST-70 date of manufacture

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ST-70 date of manufacture

Postby Bob01605 » Sat Apr 11, 2009 6:48 am

I recently had a customer ask me about the date of manufacture of his ST-70. There is a code on the bias pots that gives you a good idea of what year your amp kit was shipped out by Dynaco. This also works for the Mark II, Mark III and Mark IV amps. Below is the text of the Email that I wrote in response to his Email.

"Steve,

On the ST-70 you can check the 7-digit number stamped on the bottom of the BIAS POTENTIOMETERS. The 4th and 5th digits are the year of manufacture and the 6th and 7th numbers are what week of that year. If for example the bias pot is numbered 1386217 - then these bias pots were made in the 17th week of 1962 - probably in early May of 1962. Since Dynaco used parts very quickly you can almost be assured that this amp kit was shipped to a dealer in 1962. If your bias pot has a "48 to 52" as the 6th and 7th numbers like "1386249" then it is possible that the pot was made in 1962 but the amp was shipped out 5 or 6 weeks later in 1963.

See below a bias pot made in August of 1964 with a "1376430" code


Bob"

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Postby Bob01605 » Sat Apr 18, 2009 7:08 am

Recently I have been provided with information that some of the bias controls on the ST-70, Mark II, Mark III and Mark IV have 6 digit numbers stamped on the back and/or side of the pot instead of 7 digit numbers as seen above in my original post. If anyone has any definitive information on how these 6 digit numbers equate to a manufacture date please let us know ? Examples below ...

Bob

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Postby battradio » Sat Apr 18, 2009 8:12 am

Hi ,

The fist one is 1979 the 52nd week or Dec and the second one is 1978 and the 8th week or Feb .

Mark
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Postby wyatt » Sat Apr 18, 2009 9:07 pm

battradio wrote:Hi ,

The fist one is 1979 the 52nd week or Dec and the second one is 1978 and the 8th week or Feb .

Mark


On the year? (???) Absolutely...wrong. :(

137=CTS
9=1949 or 1959
52=52nd week

137=CTS
8=1948 or 1958
08=8th week

Which decade they came from is generally determined by context. Since I don't think Dynaco was building ST-70's and Mark III's with 1940's pots, is safe to assume these are from '59 and '58.

There are two parts to these numbers. The first three numbers are the EIA code, they denote the OEM supplier (137=CTS), they are always three digits. The date code follows after that. These have what is known as three-digit date code. A three-digit date code is the last number of the year, followed by the week.

Date codes were NOT designed to mark items for posterity but to track lots sold to wholesalers and manufacturers. There was no serious danger of lots made a decade part being confused, so they considered the decade superfluous. However, in the '60's most OEM suppliers did eventually switch to a four-digit date code, which included the decade.

Guitar amp techs that work in vintage amps will be able to name off the OEM numbers of lots of big suppliers. They get anal about this sort of thing. Off the top of my head...

137=CTS
381=Bournes
106=Allen Bradley
220=Jensen
285=Rola
274=RCA
830=Triad (Tweed Fender transformers)
606=Schumacher ('60's Fender transformers)
188= good ol' GE
336=Western Electric, grand-pappy to most guitar amp designs
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