Les Claypool

In this image we can see Les standing in front of his stage set up. The 400+ can be seen to the right of Les.

Les Claypool used one or two of these at a time placed horizontally and angled towards him for a period of time and can be seen with this setup live on several occasions.

He uses this as a head for his Mesa Boogie Subway Cabs

Les is shown in this image standing next to his live set up gear; including the Mesa Boogie 2x15 Diesel Cabinet.

In the early to mid-'90s, Les Claypool used a modified A/DA MP-1 MIDI Programmable Tube Preamp, running it through a Mesa 400+. Although definitive proof is scarce, he frequently appeared in A/DA advertisements in guitar magazines during that time, as noted in a discussion on Harmony Central.

According to Ampeg's site, it says that Les uses an SVT 3 Pro.

Here on Ampeg's official site, Les is listed as using a SVT-3PRO and SVT-4PRO heads.

Les Claypool uses the Mesa Boogie Subway® Ultra-Lite 1x12 Bass Cabinet during his tours with Primus, as highlighted by Mesa Boogie on their Facebook page.

You can see an ampeg b-15 behind Les in the music video for Wynona's Big Brown Beaver

Les Claypool used the A/DA MP-2 MIDI Programmable Tube Preamp with Primus from 1995 until the band's hiatus in 2000, as noted in the August 1991 issue of Guitar Player.

Les can be seen using an Ampeg SVT VR head as early as may 2019 (source are the dates of pictures on getty images). At 0:06 in the added Instagram Reel, the head can be seen at the bottom of his rack.

Used on basically all of 1997's "Brown Album". according to this old web interview/article, Les confirms that the main amp he used on the Brown Album was this small solid-state bass amp. he states, " for me, it's easier to get tones out of smaller, quieter amps, because you're not feeling the big sound in the room, but just hearing what the mic hears. The mic can't feel the rumble that you feel through the ground. Anyway, our success rate has been higher when we've kept the volume's down."