1936 Penn introduced the 115 senator
1937 Penn added 116 senator
1938 Penn introduced full line of senators from 113-118...
....this is an advertisement from 1938 describing the new 117 (14/0). The illustration shows wood log knob handle, and the knob is described as "torpedo type" and is made out of "lignum Vitae". I doubt they ran this advertisement for any length of time. The wood log knob is seldomly found on senators from this era. Obviously very few left the factory with this type of knob, so if you ever get a shot at one, my advice is buy it !!
There are a couple of words you don't see every day. That's very tough, dense stuff, so dense that it sinks in water. I used to have a lignum vitae mallet. As I recall, it split, and I wonder now what I could have done to make that happen.
I didn't know Penn used that wood in the past. It is native to the Florida Keys where I grew up. I learn something everyday on this site. It is protected now.