[Heathkit] can't set bias on 40 meters

[yash at aol.com]

Just cleaned up a sb-101 and put it on the bench. Set the bias to 50 MA ,dialed right in on all band positions ,EXCEPT 40 meters,Bias on 40 flew up to apx 300ma ,when I turned to the  tune position. can any one suggest a area to look at?  will start thru with the manual, in the morning,thought maybe I could get some info for a head start.
thanks for any help.
dale wt4t