Made by Seco manufacturing. Mpls, Minn, model GCT-3

It has a "magic eye" tube for the indicator, and 3 sockets.
One socket for twin triodes of the pin pattern 9A (12AX7s and
such, another for 6V twin triodes, and a 3rd for pentodes
like 6AU6s (7CM and 7BK pinouts). Doesn't seem to
work but it's not clear how to operate it. The eye tube
does glow green. Anyone familiar with Seco equipment?
If not I could trace it out; looks to be a transconductance
tester for a limited selection of tubes.