Ampeg SVT

The SVT is a stand-alone amplifier or "head" as opposed to a "combo" unit comprising amp and speaker(s) in one cabinet, and was capable of 300 watts output at a time when most amplifiers could not exceed 100 watts output, making the SVT an important amp for bands playing music festivals and other large venues.

It was not until 1980 that the speakers in the enclosures were updated to a power handling rating of 350 watts, allowing a player to use an SVT head with only one cabinet.

When The Rolling Stones began rehearsing for their 1969 U.S. Tour in Hollywood, a power conversion failure blew up all of their UK Fender amplifiers.

Their road manager, Ian Stewart contacted Rich Mandella at the Ampeg office in Hollywood, and Rich arranged for the band to use five prototype high-output amplifier heads of a new model being developed by Bill Hughes and Roger Cox.

In the early 1980s, Ampeg was bought by Music Technologies, Inc. (MTI), which contracted to have SVTs manufactured in Japan.

Cosmetically, MTI SVTs have black faceplates with white lettering, black grill cloth, "elephant hide" or rougher textured tolex, and rack case-style spring-loaded handles, updated from the previous (and painful) rubber-covered metal strap handles.

These SVTs also include a back panel selector toggle for 2 or 4 ohm speaker impedance loads and a longer and thicker gauge 3-prong power cable.

In 1986, St. Louis Music acquired the rights to the Ampeg name and took possession of all remaining MTI inventory, which contained enough original components to build 500 amps.

This sound characteristic is mostly due to 6146 being much lower in transconductance and less sensitive to drive signal, requiring a higher level from the Pre-amp, which can create more "harmonic growl."

Because the front end 12BH7 voltage amplifier is fed from the 430 V node, during loud transients and overloads this will produce an AC signal that far exceeds the 12BH7 follower that has 220 V on the plates.

By adding a 1K and filter cap feeding from the 220 V screen supply to the front voltage amp of the 12BH7, a 6146B tube runs reliably with far fewer issues.

In the event of a tube short failure or simply a transient overload condition the diode will conduct once the current in the 22ohm screen resistor reaches 30mA and beyond, preventing further burning of the PCBA.