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Identifying NATIONAL UNION tubes

This article provides examples of NATIONAL UNION-manufactured tubes. NATIONAL UNION was another quality USA tube manufacturer with most production dating from 1930s to 1950s. Their production numbers were significantly smaller than the big name brands (RCA, Sylvania, GE). The NATIONAL UNION (EIA) code number is “247″. Here is an example: (Left = Sentinel brand 6SN7GT; […]

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Identifying CBS Hytron tubes

This article provides examples of CBS Hytron-manufactured tubes. CBS Hytron was a very high quality USA tube manufacturer. Their production numbers were much smaller than the big name brands (RCA, Sylvania, GE). The CBS Hytron (EIA) code number is “210”. When you find a repackaged CBS Hytron tube, you will most commonly find 6SN7GT and

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