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What questions should I ask about an old SVT for sale

Discussion in 'Amps and Cabs [BG]' started by blockinlay, Apr 4, 2009.

  1. blockinlay


    Feb 21, 2009
    Phila Pa
    Got a line on an SVT head from the 60's. Haven't gotten too much description so far other that it was described as a gem, whatever that means.
    It seems like a fair price if it's in working order, and has a case.
    From those in the know, what questions should I ask about it?
  2. is it a blueline?
  3. Jim C

    Jim C Is that what you meant to play or is this jazz? Supporting Member

    Nov 29, 2008
    Bethesda, MD
    Does it work; how new are the tubes, are there any issues, have any service records?
    When you see it, look for abuse vs. how well it was cared for as well as any non-stock parts.
    When you play through it, listen for distortion, scratchy pots, a nice even glow from the tubes, and, magic tone.
  4. Does it have the original tube types or was it converted?
    When was the last re-cap job done?
    If it has been sitting unused, does it get fired up once or twice a year (to keep the caps in good working order)?
  5. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Thousand Oaks, CA
    John K Custom Basses
    many sellers often say that they have a "60's" SVT, however there are not too many SVT's from the 60's as they were introduced in 1969. more often than not, they are early '70s' amps, which the '69, '71 & '72 are blue line heads. they became blackline heads in '73 & '74 and in '75 went to a different faceplate with white rockers and had a rocker power switch instead of the toggles.

    a '69 often came with 6146B tubes and an extra socket for a tube relay, but many of them were converted to 6550's.
  6. reno88


    Mar 16, 2008
    how long have you owned it?
    from whom did you buy it?
    are there any mods to it?
    have you ever had any problems with it?
    why are you selling it?
  7. johnk_10

    johnk_10 vintage bass nut Supporting Member Commercial User

    Feb 16, 2008
    Thousand Oaks, CA
    John K Custom Basses
  8. anderbass


    Dec 20, 2005
    Phoenix. Az.
    One thing I'd casually ask is what cabs he's used over the years. SVT's are designed and factory labeled for 2 and 4 ohm cab loads only. I'd take it as kind of a bad sign if he'd been using an 8 ohm cab load for years...

    You'll find most very early production SVT's will either have a wire that plugs into the top of each 6146 power tube, or a small chassis hole remaining next to each 6550/KT-88 power tube if its been converted to the newer style power tubes. These very early production SVT's usualy have the most value. Most all the the 69 through 72 SVT's have blue colored etched printing on the face plate and these are usualy worth a bit more than black face SVT's.

    The quoted info below should help you estimate the age of this amp:


    The text for this section was reproduced with the kind permission of the authors of Ampeg: The Story Behind the Sound, ©1999, published by Hal Leonard. The book contains, in addition to an in-depth history of the Ampeg company, more useful technical information on the variations in Ampeg amplifiers, including color depictions of the various cabinet coverings and grill cloths. Click here for information on ordering this book directly from the authors.
    Dating Ampeg Amplifiers


    Ampegs can be divided into six distinct groups for dating purposes: pre-1953, 1953 to mid-1965, early 1965 to 1969, 1969 to 1979, 1981 to 1984, and post-1984. Each group uses a unique serialization scheme that can be used to assist in dating the amps, but in many cases, it is the features and characteristics of the amps that determine the year of manufacture.
    Electronic Industries Association (EIA) codes can also be very useful for giving clues as to an amp's age. These codes can be found on speakers, transformers, pots, capacitors, and multi-section electrolytic "can" caps. Of course, these codes are only applicable to original components, not replacement parts.

    WARNING: Ampeg amplifiers, especially the high-powered amps such as the SVT and V-series, contain lethal voltages even when unplugged and turned off. Therefore, do not poke around in your old Ampeg if you are unfamiliar with amplifier electronics or their operation.

    A brief summary of the EIA system follows.

    Shortly after World War II, American electronic component manufacturers began to stamp a semi-standardized code into the parts they produced. The code contained information regarding the manufacture and date of production. These codes have been used on components including potentiometers (pots), transformers, capacitors, tubes, and speakers.

    The code usually consists of 6 or 7 digits such as 137634 where the first two or three digits is the EIA code for the manufacturer (137 denotes CTS), the fourth digit and sometimes fifth digit denotes the year (in this case it could be 1956, 66, or 76), and the last two digits denote the week of the year. It is important to note that parts do not always contain EIA codes, especially those parts from the late 1940s and early 1950s.

    Some common manufacturer codes for parts used in Ampegs include:

    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)
    Pots: CTS (137), Stackpole (304)

    The Michael-Hull amplifiers can be narrowed down to a date of manufacture between 1946 and 1948. These amps used a serial number system that was not used by any Ampegs. Unfortunately, the serial numbers are of little help for dating one of these pre-Ampeg models and EIA date codes on components were used sporadically during the early post WW-II years. The only date codes that seems to be readily available is found on the speaker magnet located under the bell cover.
    The Ampegs made between 1949 and 1953 did not have serial numbers and must be dated in the same way as the Michael-Hull models, specifically, by finding the EIA date codes on pots, transformers, multi-section "can" capacitors, and speakers.

    1953 through mid-1965
    It appears that the serialization system used during this time period is date encoded which makes dating the amplifier rather easy. The serial numbers are 6 digits in length with the following pattern: YMMNNN, where Y denotes the year, MM the month, and NNN the Nth unit produced that month. The Nth unit, however, may not have started with 001. Ampeg may very well have used 100 or 101 as the starting point during slow production periods. Nevertheless, for dating purposes, the serial number provides adequate information during this period.
    For example, a Duette with serial number 710201 was made in 1957 (7), during October (10), and was possibly the 201st amp made that month. A Super Echo Twin with serial number 404553 was made in 1964 (4), during April (04) and may have been the 553th amp made that month (553).

    Caution is needed for dating amps from 1953, 1954, 1955, and 1960. The serial numbers from these years were duplicated in 1963, 1964, 1965, and 1965, respectively. Taking the example Super Echo Twin above, its serial number alone could denote April 1954 or April 1964. A Mercury with serial number 009054 could be from September 1960 or it could be from the second serial number system implemented in 1965. Luckily, it is very easy to determine which year the first digit denotes.

    The key is the model and the cosmetics. For instance, the Super Echo Twin was made in 1964, but not in 1954. The M-12 Mercury circuit of 1960 used 6V6 power tubes, but the Mercury circuit of 1965 used 7591As. Likewise, an Ampeg from 1954 would not be covered in blue check vinyl whereas an amp from 1964 would have this covering. An Ampeg from 1960 would be covered in navy random flair vinyl whereas an amp from 1965 would be covered in blue check vinyl. Another check for a 1960 versus a 1965 or later serial number (i.e. numbers beginning with 0) is that the second and third digits of the number denote the month in the first serial number system. Therefore, a serial number where these two digits are greater than 12 must be from the second serial number system (1965 - 69). A final cross check with EIA dated components should remove any doubt about an made during the 1953 - 65 period.

    Early 1965 through 1969
    The second serial number system was implemented in January 1965 and used until the end of 1969. This system overlapped with the previous serialization scheme for a period of about 6 months. These are also 6-digit numbers, which appear to have been applied sequentially, but they are not date encoded. Enough information (serial numbers, model, date codes) has been gathered to prepare the following guide for dating by serial number. Note that the year associated with a range of serial numbers is very rough and will likely change as more information is gathered for refining the estimates. The EIA date codes of original components should be used to confirm an approximate date of manufacture.
    Serial Number Range Year
    000001 to 020000 1965
    020000 to 049000 1966
    049000 to 075000 1967
    075000 to 080000 1968
    080000 to 092000 1969

    1970 through 1979
    The third serial number system was implemented in 1970. Not enough information was available to the authors to determine year of manufacture by serial number. An added variable is that during the Magnavox years, Ampeg may have used separate serial number systems for each model or for models that shared the same chassis like the VT-22 and V-4. Until such time that enough information is available to date 1970s Ampegs by serial number, the features of the amps from this period can be used and compared to the following table. Feature Years Used
    Blue control panel graphics 1968 - 1972
    Black control panel graphics with square corners 1972 - 1975
    Black control panel graphics, horizontally split with rounded corners (solid state amps) 1973 - 1979
    Black control panel graphics, horizontally split with rounded corners (tube amps) 1976 - 1979
    Distortion control knob 1976 - 1979
    White rocker switches (solid state amps) 1973 - 1979
    White rocker switches (tube amps) 1976 - 1979
    Black rocker switches 1968 - 1975
    Metal "a" logo 1968 - 1972
    Plastic "a" logo 1973 - 1979

    1981 - 1984
    The MTI-era amplifiers cannot be dated by serial number. Dating by EIA date codes is impossible since the Japanese components do not carry EIA codes. However, all MTI-era Ampegs were made in the relatively short time period between late 1981 and 1984.

    The modern Ampegs of the St. Louis Music era were all made after 1985. The amps made since 1988 have a 10-digit serial number which is encoded for model, country, date, and year. The serial number can be broken down as follows:

    Digits 1, 2, 3 = Model

    Digit 4 = Country Code where:
    U = U.K.
    D = domestic U.S.
    W = worldwide
    Y = Europe

    Digit 5 = Year where:
    A = 1988
    B = 1989
    C = 1990, etc.

    Digit 6 = Month where:
    1 through 9 = January through September
    0 = October
    A = November
    B = December

    Digits 7, 8, 9, 10 = serial number


    Last modified 06/16/2007 11:14:40

  9. blockinlay


    Feb 21, 2009
    Phila Pa
    That's allot of good info, thanks, and thanks for the questions to ask.
    The guy that has it is out of town, so I have to wait. Gives me time to learn and make sure it's not an impulse buy. I've been looking into new modeled amps, and am really undecided. I love vintage tube amps though. Could be the deciding factor if it's in good condition.
  10. bluewine

    bluewine Banned

    Sep 4, 2008
    Yeah, I guess for that Kind of investment you want the whole history.You don't want an amp with bad karma behind it. You might want to check the chasis for any corosion or spills.
  11. Jim C

    Jim C Is that what you meant to play or is this jazz? Supporting Member

    Nov 29, 2008
    Bethesda, MD
    or residue from a dry chemical fire extinguisher

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