A Central Pennsylvania man has been given six months in Montgomery County Prison for using a bad check to pay for silver and antiques he bought from the Alderfer Auction Company of Hatfield. 49-year-old Joseph Bova of Shamokin Dam pleaded guilty to theft by deception.   Court documents say he went to an estate auction last September and used a personal check to pay for $3,500 worth of sterling silver, cast-iron toys and other items.  After the check bounced, company employees tried several times to reach him by phone and finally sent a certified letter.  He signed a receipt for the letter, but the payment never arrived and the company reported the incident to police.