Wartime parts shortages in 1943 meant that radio repairmen had to improvise to make do with what was available, and magazines were full of tips to allow substitutions.

The diagram shown here was sent in to the July 1943 issue of Radio Retailing Today by radio serviceman M.G. Goldberg of 142 E. 4th St., St. Paul, Minn.

Goldberg noted that tubes for the standard “All American Five” circuit were hard to find, but equivalent six volt tubes were still available, and that 6 volt filament transformers were also fairly easy to come by in most areas. So one solution to the problem was to replace the series-string tubes with 6 volt equivalents, as shown here. This particular version meant that the tube sockets could be kept as-is, other than rewiring the filaments. The article also suggested other possible substitute tubes, although other substitutions would require rewiring the sockets.