This is a historic Ampeg SVT prototype number 9.

Amp is all original, including signal tubes and is in beautiful working order. And it sounds phenomenal!

Serial numbers matching dating to July 1969.

Ampeg prototypes reportedly have single numbers written in magic marker during the builds. This one is number 9 - just a big "9' in a circle on both the preamp and amp chassis.

For the July 1969 date of manufacture, further researching reveals it's a 90% chance this amp one of a handful (5 plus spares) that were given to the Rolling Stones for their famous/infamous Nov - Dec 1969 tour when their own gear got destroyed. That tour is what began the SVT legacy. This amp, for the date codes and relative provenance, may be valuable ( first edition and Rolling Stones) as a collectible more than later SVTs.

The provenance relating to this as a prototype and thus the Rolling stones, is best described here from Ampeg directly: "... In a panic, now deceased Stones keyboard player and road manager Ian Stewart contacted Rich Mandella, Ampeg's Hollywood liaison, desperately begging for amps for the tour that was at that point only weeks away.

Mandella, knowing a good thing when he saw it, loaded up all the SVT prototypes and some old 4x12 cabs into his pickup and headed down to the Warner Brothers lot where the Stones were rehearsing. Keith, Mick Taylor, and Bill Wyman plugged in to the SVT prototypes and proceeded to turn them up to a level that reduced the un-hip to flaming piles of goo. The Stones may have had sympathy for the devil, but they gave no such kindness to the SVT prototypes, and Mandella noticed that the prototypes were getting close to meltdown under Keith's relentless bashing. According to Mandella, "Everything he was doing in rehearsal just kept getting louder and bigger and crazier, with two or three heads per person. I'd watch the amps, and when I could see one was about to explode, I'd just switch heads."

Since those prototype SVT heads were the only ones in existence—production was still aways away—it was decided in a very smokey room that Mandella would accompany the Stones on the tour as their personal Ampeg technician.

This SVT was made in July 1969, before the official release of the SVT as a product. These earliest SVT used 6146 tubes instead of the later, more ordinary 6550. As everybody knows, 6146 are transmitting tubes used as driver exciters for TV broadcast and power tubes for police, fire and Ham radio. The prototype SVT's seems to be the only instance of them being adapted to an audio power amp.

Video for the amp where I show you how it sounds:

https://youtu.be/UqrpFcUVhkE?si=ELtZTdZo8AGmQWAf

I found an excellent Ampeg site: https://www.fliptops.net They have a bespoke cap kit for this amp: https://www.fliptops.net/catalog/p-100083/cap-kit-for-ampeg-svt-v9-w6550-v.2. I could do otherwise except I like the custom job they did to re-make the triple can cap like original.

Correct link for the 6146 version cap kit https://www.fliptops.net/catalog/p-100082/cap-kit-forvintage-ampeg-svt-with-6146-tubes. I stock many of those caps. Pondering just ordering the one can: https://www.fliptops.net/catalog/p-100158/70x40x40450v-multicap or possibly doing a restuff of the original:

https://m.youtube.com/watch?v=sPJMPdcJqYs

Another version of the 1969 Tour story:

On November 27 and 28, 1969, the Rolling Stones headlined Madison Square Garden with opening acts Terry Reid, B.B. King, and Ike and Tina Turner. The New York Times declared it “the major rock event of the year.” The Stones’ backline? A wall of Ampeg SVTs. Eight SVT heads perched atop 8 x 10″ cabinets powered Keith Richards’s and Mick Taylor’s guitars, as well as Bill Wyman’s bass. Ampeg totally lucked into this phenomenal public relations coup. Months earlier, the Stones had shipped their own amps to Los Angeles to rehearse for their upcoming US tour. However, it wasn’t until they switched them on and they blew up that they realized the amps were set up for UK voltage. Luckily, Ampeg was in a position to capitalize on this most unfortunate of circumstances. You see, Ampeg had a new super amp — the SVT — and it was a beast. There was only one slight problem: it was still in the beta stage.

With the first tour date only weeks away, Stones keyboard player and road manager Ian Stewart reached out to Ampeg’s Hollywood rep, Rich Mandella, who saw an opportunity, loaded up all the SVT prototypes and some old cabs into his truck, and headed over to the Warner Brothers lot where the Stones were rehearsing. Richards, Taylor, and Wyman plugged in and cranked the 300-watt behemoths up to face-melting levels. Rich kept a wary eye on the amps (which immediately started showing signs of stress), and when he noticed one was about to fry, he’d swap it out. Since production was still months away and those prototype SVT heads were the only ones in existence, it was decided that Mandella would accompany the Stones on the tour as their personal Ampeg tech to patrol behind the backline and make sure everything was copacetic. The Stones’ soon-to-be-legendary ’69 tour was off to an auspicious start — quite the baptism by fire for Ampeg’s new amp.