Heh guys -- new user here, Well I am working on an electronic organ project from Forrest M. Mimms the III book "Getting Started in Electronics" from Radio Shack page 108. The circuit calls for a 2n4891 unijunction transistor which is now obsolete and very expensive. I know I can substitute a 2n6028 PUT that will do the job but I need to know the values of the programming resistors to make the substitution work. Please explain in depth as I am new to the field of electronics. An attached schematic would be nice. Thank you so much for your help with this issue! johnnyinwa.