FWIW there appears to be a schematic at :

http://www.vintage-radio.info/downlo...le=sb-1000.zip

I got it and unzipped it and it looks clean. A PDF result form Google comes wuith a warning from google about "harm your computer" so I didn't get that.

If there is plate voltage then there is, that part works. If something went poof it is probably in the cathode circuit, if anything is. If not then in the grid circuit. If so, that tube is probably shorted of has alot of leakage of some type.

In fact without drive it probably should be redplating.