Re: dubious
That's a HF one - as evidenced by the connector - relatively low power - and can't be any good for more than about 10-15MHz.
It wouldn't last long attached to the output of one of THESE: http://maritimeradio.org/himatangi-makara/himatangi-radio/harris-collins-1_1200/ (I spent quite a bit of time in the back of the left hand unit (#118) in 1989-90 keeping it running long past its use-by date)
Scarily, all four of the pictured units were originally intended as ship transmitters, not for shore use. (Even more scary was the fully operational 100kW late 1940s era transmitter opposite them.)