Hi Mark; that's quite an amp!
GA45 RVT Schematic Here 50 watts of bruising Gibson 6L6 power and, because the Gummint stopped the commerical use of cobalt in the mid-60s, unusual to find alnico speakers with such late dates. Cosmetically, this is a 'white face' or 'dog house' model referring to the control panel and the knocked-off ears of the cabinet. Two channels with twin inputs; trem and reverb on channel 2. Didn't quite understand seller's remarks about the reverb transformer. This is a robust, gigging amp and not a museum piece; it can take a Fender or equivalent transformer and keep on ticking.
This amp relies on the much-misunderstood 6EU7 in the preamp. While there's a lot of 'cork-sniffing' associated with 12AX7s, with one exception and with different pinouts, the 6EU7 - like a 12AX7 - is just another twin triode but without the panache. Apart from pinouts, the filament or heater wiring is different from the 12AX7s which are wired 'humbucker' - built in propensity for noise cancelling like a humbucker pickup - while the 6EU7 isn't and gets hung with the 'noisy' tag. Gibson used the 6EU7 in a number of it's designs; GA5 Skylark ('Crest'), GA19RVT, GA30, and others. They are readily available NOS/NIB at about $20/ea although they will start to crawl up in price. People - like me for instance - are hesitant to re-wire 6EU7 sockets to accept the easily-located, less-costly, and better-regarded 12AX7.
Lacks some of the goodies like line out, effects loop, master volume, and channel switching by footswitch found on amps in the later 60s but no reason to doubt seller's characterization of tone; clean and loud is what 6L6s do. CJ