PA250

The advertisement in "Radio", Nov, 1929 page 61 shows that this tube was fitted with the patented ceramic Perryman Bridge. This was two special spacers one placed between the press and element base. This had the necessary wires pass through it for sturdiness, insulation and parallel alignment. The second bridge was placed on top of the element structure. In directly heated tubes, the filament was also held in place with a tension spring. This element structure would have been expensive to make and it is not known how long this tube variation was commercially available.