THis is a master volume bassman I believe dates to 1973 according to the transformer dates. Healthy sounding and working well. Has had some servicing in its life as the sound tech I purchased it from said it came from a working and touring band. The badge affixed in back should attest as well to someone giving it a go through. I know of no mods, and the transformers all seem original.  I photo'd the serial of the two I could see.