Mark - The keying circuit is almost identical, grid block keying with the -60 VDC bias supply. 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 4-B, C-Line& TR-4/C Service Supplement CDs <www.k4oah.com> mlangen wrote: > Anybody know the voltage across the key on a TR-6? Same as the TR-4? > > Tnx, > > Mark -- WA9ETW > >