| I can tell you that it wasn't really a bass amp.
It was marketed as a lower powered all purpose amp; guitar keyboards, bass, but has the same tone stack as the Sunn guitar amps of the day combined with the smaller 40 watt 2xEL34 output section.
It also was only available with a single JBL D130 in a shallow (11.5") what Sunn usually considered to be a guitar cabinet configuration.
Sunn dedicated bass amps came with D140's in the '67 -'68 models, with the exception of the low cost Sonaro, which was a combo featuring "1 - 15" heavy duty Sunn Bass Transducer", which I'm pretty sure was made by CTS.
It was replaced in 1969 by the Sentura I, which was the same amp and cab as the Spectrum I but with reverb and "vibrato" (tremelo).
It should sound great for bass through the proper cab. I have a similar, very early split chassis 2xEL34 Sunn Model 40 that I use with a D140 loaded Sonic I40 cab for practice/recording. Power and volume wise it's similar to my Ampeg B15N; a little more headroom, cleaner with deeper bottom and crisper highs, but lacking the B15's tasty, warm, comfy "feel good" tone. | 
