History of the manufacturer National Union Radio Corp.; Orange (NJ) https://www.radiomuseum.org/dsp_hersteller_detail.cfm?Company_id=2955 https://www.radiomu

History of the manufacturer National Union Radio Corp.; Orange (NJ) https://www.radiomuseum.org/dsp_hersteller_detail.cfm?Company_id=2955 https://www.radiomuseum.org/dsp_hersteller_detail.cfm?Compan... Not only an adder, you could probably mix audio channels and create interesting effects. In the Space Age, building 300VDC power supplies was basically a prerequisite for any teenage electronics hobbyist. The BG2 tube was probably not mass produced. This looks like a design that NU made prototyes of and was willing to manufacture if enough interest developed.