1 low noise microphonic single tube) 5687 Tungsol ribbed black plates "U" getter like new 1952 in white box

1 section) 37.5ma Gm=11,000 

1 section) 40.0ma Gm=12,400

1ST SERIES MADE BY TUNGSOL (1949-1953 era)

BLACK RIBBED PLATES

322 = Tungsol factory code

224= date code 1952, 24th week

Tested on Amplitrex

Vplate=120V

Vgrid=-2V

Good Ma range 30-35ma

Good Gm range = 10K-12K

Recommended for

Manley

Modwright

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Ray Samuels

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Kondo

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Loth