[Texasrocker]

Hello Codefox. I looked for the Sparton schematic ( mod 813) in JF Riders, also known as Sparks-Withington chassis, both American & Canadian versions and couldnt find a mod 813 listed. However, since it is a battery-type set, the tube-filament string needs to be complete ( replace the missing tube) before attempting powerup, so the filament voltages "add-up" to correct incoming DC current are correct before attempted powerup at all. Otherwise, you risk the chance of ruining ( burning-out)all the other tube filaments in the filament string in the 1.5 volt types tubes, if your set has those type tube thru-out the circuitry. If you want to use only 1 audio tube, if you have a spare 3V Audio type tube to replace 2- 1.5v types, ( check your RCA tube manual for a good sub), change out to "1" audio-tube (correct socket basing)socket that uses a 3-volt filament audio-tube doing necessary-socket wiring mods under chassis first also. A 3v filament tube will replace 2- 1.5 volt filaments tubes in some sets by careful mods. It would probably be worth your while to check all your tube-filaments with a (1.5 Only) volt battery type continuity-tester, and replace all tubes that have "open" filaments ( if any), and go ahead and add another tube of proper type to replace your missing audio tube before trying any power-up attempts! Those 1.5 v filaments are very-fragile, and can be permanantly damaged very easily! Those type tubes arent as "forgiving" as the 6.3 v types tube filaments for "testing" at all. If you use a continuity-tester to check your remaining tube filaments, make sure your not using a continuity tester powered with a 9v battery! That can fry the remaining orig tube filaments in a heart-beat! The orig 1.5 v tubes are generally cheap$$, except for the 1L6 types. Since I couldnt find the schemat for your Sparton radio, do you have one already? Perhaps I overlooked something here. Just trying to help. Good luck, restoring your vintage Sparton Radio, and yes, building a suitable DC pwr supply isnt hard at all !