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The 1960s military spec Mullard CV2748 / GZ30 rectifier tubes in this precisely matched pair are 5Z4 equivalents. These slow-rise, indirectly-heated rectifiers should be considered an upgrade for 5Y3 tubes in most circuits, and will drop slightly less voltage.
They have gray plates, bottom O getters, and brown bases. The white print on the glass reads \"CV2748 KB/DA\" and the Blackburn, UK factory codes are etched in the glass.
Both tubes test as new. They are tested on an Amplitrex AT1000 tester and in a custom power supply that duplicates typical operating conditions. Original boxes included.
