[Hallicrafters] sx-62a mod

[Charles]

I purchased the subject receiver on eBay and it works great! I went ahead and decided to replace all the tubes and ordered them using the parts list in service manual. 

There are sixteen tubes according to the parts list; however in the process replacing the tubes I came up one short? There is an extra  6C5 that is physically located next to V-16(6C4). I haven't pulled the bottom off to see where the circuit is added, but wondered if there is a "known" mod that would explain the additional tube?
.

Charles Knight
"Time is the best teacher. Unfortunately, it kills all its 
pupils." --Hector-Louis Berlioz