"Sunn Amplifier Coliseum PA System"

Sunn introduced its powerful "Coliseum PA system" ca. 1965 and it gained favor with bands (like "The Beach Boys") for its high-fidelity, full-frequency reproduction.
The speaker system included left and right side stacks consisting of two 15" JBL 130AS cone speakers for the bass with JBL crossovers built into the backside of the 42" X 24" X 15" cabinet.
On top sat a separate cabinet housing a "JBL 375" midrange compression driver coupled to a JBL horn/lens, giving wide dispersion of sound.
The high frequencies were handled by a "JBL 075" 'bullet' tweeter built into the top corner of the 2 X 15" cabinet's baffleboard.

This passive three-way system was about as good as a speaker system got until active crossovers became popular in the '70s.
The head is most important to this story, as guitarists and bassists shunned the expensive and inappropriate full-range speakers in favor of multiple-cone speaker cabinets with limited high-frequency response.
It was the powerful stock Coliseum head "Jimi Hendrix" used early-on (early 1968) in place of Sunn's suggested 60-watt 100S head, with the company supplying 4 X 12" cabinets to suit his preference.

Jimi Hendrix in February 1968 with 100-watt Sunn Coliseum P.A. tube amps.In 1968, Hendrix agreed to a 5 year contract with Sunn Amplifiers. In exchange for all the free equipment that the Experience needed, Hendrix agreed to offer his input for research and development. Hendrix started out with a 100S cabinet, loaded with one JBL D130 in the bottom and a LE 100S driver horn in the top. Later, the Sunn setup included up to five Coliseum P.A. tops - altered for guitar at 120 watts RMS each - with ten speaker cabinets loaded with two JBL D130s each.

Jimi Hendrix 28/2/1968

These heads were designed to be high-fidelity but like any tube amp, especially one designed to accept low-output microphones, they would break up when pushed.
The Coliseum used four KT88 power tubes in a push/pull ultra linear circuit.
The transformers were from the large Dynaco mono blocks.
It's interesting the amps were only rated at 120 watts RMS, because everyone else claimed 200 watts from the same arrangement.
It's probable the transformers weren't large enough to develop the extremely high plate voltage necessary for full power, or that the ratings were on the conservative side (they gave the peak power with negligible distortion as 280 watts).

Pete Townshend in 1967 used the Sunn 200S 2x15" rear-loaded folded-horn enclosures, which would have two JBL D140. Pete also appears to have occasionally used the Sunn 100S cabinet, which was the same size but featured one JBL D130 and one JBL LE100S midrange driver with high-frequency acoustic lens/horn. Both the 100s and 200s cabinets were 42" high x 24" wide x 15" deep.

The individual volume controls for each of the four channels were coupled to a Master Volume control, although the people using these as guitar heads probably put both on 10.
Having a separate preamp tube for each channel would have allowed players to jump channels and get a fuller sound at lower volumes, as would become popular with two-channel "Marshall amplifiers" (the later single-channel instrument Sunn models had all four inputs ganged to a single preamp).
A total of three twin-triode 12AX7s handled the four input stages, leaving two stages for additional gain, a 6AN8 acted as the phase inverter and a pair of 5AR4 rectifiers supplied the juice. Separate bass and treble controls rounded out the features.
Price for the entire system in early 1968 was a whopping $3,695, without covers.
By April 1970, the "JBL 075" bullet tweeter and its crossover network were gone and the price dropped to $3,495.
In the early '70s, Sunn expanded heavily into PA manufacturing, offering numerous solid state heads of varying wattage, with the tube Coliseum being retired.
"Randy Holden" used "Sunn Amplifier" on "Population II" album.