Great quad of Raytheon 6SN7GTB bullet black plate grail tubes. All tubes are date/code matched “280 58-34” and are closely matched for transconductance. All tubes have been thoroughly checked out on my calibrated Hickok 752a tester.

Here are the results of the mutual conductance testing: (average minimum good reading for this tube on this tester=400)

1) 675/675

2) 650/700

3) 675/675

4) 675/700