The 221 is an 201A but with different filament ratings. It was made almost exclusively for export and had very little use in the United States. Due to the very low filament current required, the tube may be operated on dry cells or a storage battery. Some tubes have been found branded RCA-221 and RCA 221
Dimensioni (LxAxP) incl.pins/tip
x 108 x 45 mm / x 4.25 x 1.77 inch
Peso
47 g / 1.66 oz
Bibliografia
-- Collector info (Sammler)
Tube Lore (II) Page 25 & 30
UX221: RCA Tube Manual
Peter Steffen
Just Qvigstad
UX221: own collection
Peter den Boer † 2025
Segue ...
