SUNN Concert PA for bass?

It's a 100-watt, first-generation solid-state amplifier from about 1971...personally, I wouldn't get too excited about it. I believe I did read where Leslie West played through a Sunn PA head in the early days, but I think that was a Coliseum series...they were rated at 300 or so watts. If it's like most of the early vintage solid-state amps, I reckon it would have a certain real 'grit' to it, but whether or not it's a useful sound would be up to the user. I certainly wouldn't expect it to be anything special, especially not for a bass amp. Just IMO, of course.

Now, having written that, I expect we'll be hearing from players who believe it possesses some of the most magic mojo ever manufactured.

 

I found an article, this one in Guitar Player (https://www.guitarplayer.com/players/leslie-west-decodes-his-mississippi-queen-tone) where Leslie West claims it was a Coliseum PA head, but goes on to describe it as having 4 KT88 output tubes. So nothing like this solid state head. Those early Sunn tube amps employed the Dynaco hi-fi power amps designed by Dave Hafler, which were about as good as any amps made in the day. They also appropriated the Dynaco pre-amp circuit from the highly regarded PAS-1 hi-fi preamps for their input stage. All the Dynaco stuff was available in kit form (with extensive documentation), which probably figured heavily in Conrad Sundholm's decision to go that route. At any rate, these were the amps Sunn built their early reputation on. Like pretty much everyone else, they struggled some in the transition over to transistors, and this Concert PA amp is part of that first-generation effort. They did a lot better than Fender did with their first attempt at solid-state, but still.... ?

 

That transistor Concert PA Control Amp was rated at 90 watts RMS, introduced in 1969 I believe.
The Coliseum PA amp Leslie West used in Mountain (and the Beach Boys actually used as a PA amp) was an, albeit conservatively rated, hand wired, all tube 120 watt amp.
As a side note, I'm pretty sure Mountain got those amps from the Jimi Hendrix Experience when Jimi's Sunn endorsement expired.
Sunn also produced a 60 watt all tube Studio PA using the same preamp configuration.

Leslie West's Coliseum had the same hi-fi output stage as the venerable Sunn 2000S bass amp, but with an additional half of a 12AX7 in the 1rst stage for more gain, as it was intended to amplify dynamic microphones - not even remotely close to the early Sunn transistor amp you found, tonally or in market value.

The original Sundholm era Coliseum and Studio PA amps made outstanding bass/guitar amps, a little higher gain than the other very hi-fi Sunn offerings.
That transistor amp would likely sound kinda thin and anemic by comparison; "warm and tube-ish" takes actual tubes, but for $55 who cares?