IT-21 info please...

[Fred Olsen]

Sandy, the IT-21 "checker" DOES check Compactrons, but it's only an
emission checker; just an upgrade of the "TC" series.  It was available
through most of the '60s.  It has sockets for 4, 5, 6, 7, octal, loctal,
Compactron, 7 mini, 9 mini, 10 mini, 5 and 7 Nuvistor.

The only Heath Gm "tester" (that was the distinction) was the TT-1 or
TT-1A, based on the excellent Weston designs.  The TT-1 needs the
TTA-1-1 kit (new lid with remote chassis) to convert it to a TT-1A, to
test Compactrons and other 'moderns'.  Any TT-1A might be either an
original or a converted TT-1.  They are interchangeable.

Best regards,
Fred