Following on from my problems with the left channel sound, it seems as though the tape head is faulty.  It reads an open circuit when testing the left channel of the head.  The right channel reads OK at about 250 ohms.  The soft sound I was hearing was bleed from the right channel. To compound my problems, I think the the left channel is also faulty as when I connect the working right channel in the head to the left channel input there is still no sound. Does anybody have a source for the tape heads?