Squeal in a "Grace"

[DaveBullard]

My Grace has a squealing issue at max gain/volume. Sounds exactly right otherwise...
I built it on the funky radioshack board for IC's with a very compact layout and grounded everything to the same place(ala "star") with short wires to everything. he schem I used has no bypasscap hanging off the IC, but the 386 datasheet showes it in every example. I wondered about that bypasscap and tried a 100uF electro from pin7 to ground with no discernable (to me) effect. When I touch the jumper for the bypass cap that I installed, the squealing goes away, why??? This initially convinced me that I needed a bigger cap, guessing that I was a rather large value cap, but I know so little theory that I really can't figure it out. Something with the grounding I bet, or the lead length to the drive pot? I have no idea and after some searching I found no answers here specific to the Grace... so I turn to you...?Ideas?
thanks