How to determine the date of your Ampeg

Ampeg Amplifier Dating Guide

Please note: The following information was originally sourced from The Unofficial Ampeg Page, which is no longer online. It was archived via Google cache and originally reproduced with permission from Ampeg: The Story Behind the Sound (©1999, Hal Leonard).
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Overview

Ampeg amplifiers can broadly be divided into six distinct eras, each with its own serialisation system:

  • Pre-1953
  • 1953 to mid-1965
  • Early 1965 to 1969
  • 1969 to 1979
  • 1981 to 1984
  • Post-1984

While serial numbers can be helpful, accurate dating often relies just as much on physical features, components, and construction details.

Using EIA Codes to Date Amps

Another valuable tool for dating Ampeg amplifiers is the use of Electronic Industries Association (EIA) codes.

These codes can typically be found on:

  • Speakers
  • Transformers
  • Potentiometers (pots)
  • Capacitors
  • Multi-section electrolytic “can” capacitors

Important:
EIA codes only apply to original components. Replacement parts will not reflect the amp’s manufacturing date.

⚠️ Safety Warning

Ampeg amplifiers, particularly high-powered models such as the SVT and V-series, contain lethal voltages — even when unplugged.

If you are not experienced with amplifier electronics, do not attempt to open or service your amp.

Understanding EIA Codes

Following World War II, US electronic manufacturers began stamping components with semi-standardised identification codes.

A typical EIA code looks like: 137634

This breaks down as follows:

  • 137 → Manufacturer (e.g. CTS)
  • 6 (or 63) → Year (could represent 1956, 1966, or 1976 depending on context)
  • 34 → Week of manufacture

Note:

  • Not all components carry EIA codes
  • Early components (late 1940s to early 1950s) often lack them entirely

Common EIA Manufacturer Codes

Speakers

  • Jensen (220)
  • CTS (137)
  • Eminence (67)
  • Quam (270)
  • Rola (285)
  • Altec (391)
  • Electro-Voice (649)

Capacitors

  • Pyramid (472)
  • Cornell-Dubilier (34)

Transformers

  • Acrosound (878)
  • Stancor (138)
  • Electrical Windings (682)
  • Todd Electric Co. (926)
  • Standard Electric Products (668)

Potentiometers (Pots)

  • CTS (137)
  • Stackpole (304)

Dating by Era

Pre-1953

Early Michael-Hull amplifiers (circa 1946–1948) used a non-Ampeg serial system, making serial numbers largely useless for dating.

Ampegs produced between 1949 and 1953:

  • Typically did not have serial numbers
  • Must be dated using EIA codes on components
  • Speaker magnet codes (under the bell cover) are often the most reliable

1953 to Mid-1965

During this period, Ampeg used a date-encoded serial number system, making identification relatively straightforward.

Format:
YMMNNN

  • Y = Year
  • MM = Month
  • NNN = Production number

Examples:

  • Serial 710201 → October 1957
  • Serial 404553 → April 1964

However, use caution:

Some serial numbers were reused in later years, including:

  • 1953 duplicated in 1963
  • 1954 duplicated in 1964
  • 1955 duplicated in 1965
  • 1960 duplicated in 1965

How to Resolve Serial Number Ambiguities

When serial numbers overlap, rely on:

1. Model history

  • Some models simply did not exist in earlier years

2. Circuit design

  • Example:
    • 1960 Mercury → 6V6 tubes
    • 1965 Mercury → 7591A tubes

3. Cosmetic details

  • 1954 → No blue check vinyl
  • 1964 → Blue check vinyl
  • 1960 → Navy random flair vinyl
  • 1965 → Blue check vinyl

4. Serial number structure

  • If the “month” digits exceed 12 → likely post-1965 system

5. EIA codes

  • Always use component date codes to confirm your conclusion

Early 1965 to 1969

A new serial number system was introduced in early 1965 and ran through 1969.

Key characteristics:

  • Still 6 digits, but no longer date-encoded
  • Numbers appear to be sequential only
  • Overlapped with the previous system for approximately 6 months

Because of this:

  • Serial numbers alone are not reliable for exact dating
  • You must use a combination of:
    • Component date codes (EIA)
    • Model details
    • Construction features

Serial Number Ranges (1965–1969)

For Ampeg amplifiers produced during the mid to late 1960s, the following serial number ranges provide a rough guide to year of manufacture:

  • 000001 to 020000 → 1965
  • 020000 to 049000 → 1966
  • 049000 to 075000 → 1967
  • 075000 to 080000 → 1968
  • 080000 to 092000 → 1969

Note:
These ranges are approximate and should always be cross-referenced with component date codes and physical features.

Identifying Features by Era (Late 1960s to 1970s)

During this period, visual and functional features become especially useful for dating Ampeg amplifiers.

Control Panels

  • Blue graphics → 1968 to 1972
  • Black graphics with square corners → 1972 to 1975
  • Black graphics, horizontally split with rounded corners (solid state) → 1973 to 1979
  • Black graphics, horizontally split with rounded corners (tube amps) → 1976 to 1979

Switches

  • Black rocker switches → 1968 to 1975
  • White rocker switches (solid state) → 1973 to 1979
  • White rocker switches (tube amps) → 1976 to 1979

Logos

  • Metal “a” logo → 1968 to 1972
  • Plastic “a” logo → 1973 to 1979

Controls & Features

  • Distortion control knob introduced → 1976 to 1979

1970 to 1979 (Magnavox Era)

A third serial number system was introduced around 1970. However:

  • There is insufficient data to reliably date amps from this era using serial numbers alone
  • Ampeg may have used multiple serial number systems simultaneously, particularly across different models or shared chassis designs (e.g. VT-22 and V-4)

As a result, dating 1970s Ampegs relies heavily on physical features, including:

  • Panel design
  • Switch types
  • Logos
  • Circuit design and components

Comparing these characteristics against known production changes is currently the most reliable method.

1981 to 1984 (MTI Era)

Amps produced during the MTI era present additional challenges:

  • Serial numbers are not useful for dating
  • EIA codes are generally absent, as many components were manufactured in Japan

However, this period is relatively short, with all MTI-era Ampegs produced between:

Late 1981 and 1984

Post-1984 (St. Louis Music Era)

Modern Ampeg amplifiers (from 1985 onwards) use a structured 10-digit serial number system, which provides detailed manufacturing information.

From 1988 onwards, the serial number format can be decoded as follows:

Digits 1–3 → Model
Digit 4 → Country code

  • U → United Kingdom
  • D → USA (domestic)
  • W → Worldwide
  • Y → Europe

Digit 5 → Year

  • A → 1988
  • B → 1989
  • C → 1990
  • (continues alphabetically)

Digit 6 → Month

  • 1–9 → January to September
  • 0 → October
  • A → November
  • B → December

Digits 7–10 → Production serial number

Final Notes

While serial numbers are helpful, they are rarely definitive on their own. The most accurate dating method combines:

  • Serial number analysis
  • EIA component codes
  • Visual and construction features