American Muscle: The Ampeg SVT story

Discussion in 'Amps and Cabs [BG]' started by Voodoo Guitar, Oct 12, 2016.

  1. Voodoo Guitar

    Voodoo Guitar

    Oct 12, 2016
  2. BadExample


    Jan 21, 2016
    Great lunch read! Thank you.
    Voodoo Guitar likes this.
  3. The author (almost) got everything right, too!
    Hobbes likes this.
  4. Gravedigger Dav

    Gravedigger Dav Supporting Member

    Mar 13, 2014
    Springtown, Texas
    Okay, wighat, what was wrong? Just curios.
  5. Bass Growler

    Bass Growler

    Jul 10, 2015
    Great article, thanks.
  6. Raw N Low

    Raw N Low If I can't hear it, hopefully I'll feel it Supporting Member

    Jul 16, 2009
    Denver, Colorado
    Thanks for the post. Hoping to own an original SVT someday.
  7. BassmanPaul

    BassmanPaul Inactive

    OP, you have to remember that some of the folks on this site are extremely knowledgeable about the history of the SVT and could probably add you your piece.
  8. coreyfyfe

    coreyfyfe Supporting Member

    Nov 19, 2007
    boston, ma
    Bill Hughes has certainly provided some interesting tidbits on the development and early years of the SVT on more than one occasion

    1968 SVT: myth or reality?

    Just got a '69 SVT for $500
  9. BadExample


    Jan 21, 2016
    That kind of thing can be tough to find, much less verify. It's not like it's in the history books. I imagine there is more bass history known here at TB than anyone could dig up by research.
    alaskaleftybass likes this.
  10. Voodoo Guitar

    Voodoo Guitar

    Oct 12, 2016
    Thanks for the kind words guys, appreciate it! I did indeed get some great info & corrections from posting here, and value it tremendously! as someone wrote above, it's not in the history books... and thats exactly why i started my blog.
  11. Teacher


    May 3, 2012
    Great read, thanks!
  12. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    A couple of minor points.

    The V4 and family was rated at 100W with 7027A power tubes, and 130W with 6550 tubes. The 6550 performance package was an option offered. No modifications were required, just install the tubes. I would want to optimize the power tube bias. See the TB portaflex wiki, literature section, V4 brochure page 2: 1970's Ampeg V4 Brochure.

    The first revision of the SVT had an extra (15th) tube, a time delay relay. This wasn't included on the tube chart.

    Time delay relay tube.
    rodl2005 likes this.
  13. Voodoo Guitar

    Voodoo Guitar

    Oct 12, 2016
    AH!! you just cleared up some confusion i had on the V series amps... i've found conflicting info on them being either 100/50w or 120/60w... someone would always "correct" me when I had one or the other description. Those RMS ratings would vary a bit with bias settings and variances in 7027As anyhow, let alone the more powerful 6550A. This is great info.

    Thanks for this!
    Last edited: Oct 13, 2016
  14. I emailed the author, J.P. Henry (probably @Voodoo Guitar?). He was very gracious and said he appreciated my comments. Here is my email:

    "Great article! Very thorough. People don't bother to get the facts right and you did. I am an Ampeg collector and amateur historian. I thought you would appreciate my bringing to your attention a couple of details you may want to edit in your article :).

    The original V4 family of amps (V4, V4B, VT-22) were all rated by Ampeg at 100 watts, not 120, even though general consensus is they may be able to put out a handful more clean watts.

    Also, your phrasing of "after the testing period with the Stones" on the '69 tour is a little misleading time-wise. The switch to 6550A tubes happened sometime in mid-'70, so fair enough. The first run of 1969 6146B-equipped amps with the quickly-omitted relay tube feature are very rare. Bill Hughes told me only 50 or so were made (I have one). A few more were sold with 6146B's but no relay tube. I believe all the Unimusic and Magnavox era 810's were rated at 240 watts regardless of whether they had CTS or Eminence drivers. Now, the first single 810 to even THINK about being able to handle the full output power of an SVT (600 watts with peaks) would be made by MTI (rated at 400 watts IIRC) in 1981 a decade after the Stones tour. A single 810 capable of truly handling a cranked SVT's power would not be made until SLM took over. Not sure of the exact year on that, probably from the get-go in '87."

    I'm not absolutely sure about the power-handling timeline. 240 watts for all Unimusic and Magnavox era cabs, right, or did latter-day Magnavox cabs go up somewhat in power-handling? Hopefully someone can verify on the 400 watt rating of the MTI cabs as well. @beans-on-toast ? @JimmyM ?
  15. JimmyM


    Apr 11, 2005
    Apopka, FL
    Endorsing: Yamaha, Ampeg, Line 6, EMG
    I am almost sure that the Magnavox cabs didn't do any better than 240w. The speakers in them look suspiciously like the CTS alnicos, except they had ceramic magnets.
    Chris 'Wighat' Jordan likes this.
  16. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    The SLM 810E/AV cab used 100W speakers, 800W RMS total.

  17. Voodoo Guitar

    Voodoo Guitar

    Oct 12, 2016
    I was told that somewhere in between the original 30w and later SLM 100w drivers there were 50w speakers used in some of the pre-MTI cabs, but it could be false info. General consensus seems to be that you can get the volume up enough for most needs on a single 240w cab without doing any damage regardless.
    Last edited: Oct 13, 2016
  18. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    After the CTS, there was an eminence square, then round magnet speaker.

    It is important to note that the engineer that founded Eminence came from CTS. So the Eminence 10" that Ampeg first used was derived from the CTS speaker. There's an interesting eminence video that goes into the history of the company. Ampeg was buying their products from the early days.

  19. Voodoo Guitar

    Voodoo Guitar

    Oct 12, 2016
    Yep, that would be Bob Gault... it's all in the blog ;)
  20. Voodoo Guitar

    Voodoo Guitar

    Oct 12, 2016
    Hey guys, any idea if the B-25B is related to the SVT design at all? I see it's got the 7027As but thought it predated the SVT by a year or two.
  21. Primary

    Primary TB Assistant

    Here are some related products that TB members are talking about. Clicking on a product will take you to TB’s partner, Primary, where you can find links to TB discussions about these products.

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