So I had on order a new set of rectifier tubes for it 6x5wgt/5r4gy.
If only all repairs were that simple! Strange tube combo, though - are they the stock tubes, or subs added by a previous owner? I've never seen one using those tubes, not that this means much.
My SP-100 started munching fuses every few days, so I installed a new 5Z3 and 80, and all is well.
Considering how nice they sound in stock form driving a good speaker, I'd say they're excellent receivers, considering it's a 1930s design.
Have fun with it John.