I made several mods on my 100.  don't remember them all but one was a 
spotting button to get on the qrg.  another was having the V F O tube run 
all the time while transmitting for more stability and keying the next tube 
with grid block type keying maybe the 12 B Y 7. another was neutralizing the 
finals with a wire bent in one direction or another to avoid self 
oscillation.  boy these thoughts bring back a lot of memories from the 60s. 
73
Ed K7UC