Quote:
Originally Posted by Techman
When buying valves over the internet, beware of any that don't look new, but are in original boxes, as they're likely to be old faulty ones that the repair man put back in the box that the replacement came in and which never got thrown away.
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Yes. If the valve label/writing is in green, it will very likely be the faulty original valve put back in the box. New replacement valves tend to have black labels/writing.
Genuinely NOS valves can often be stored in damp conditions, which can cause the metalising (the grey coating on the valve) to stain or come off, or cause some corrosion on the pins. But is usually easy to tell the difference between damp storage and dirt from being exposed in the radio set.
Mazda changed the design of their valve boxes a number of times between the 1930s - 1960s, and the labelling on the valves changed too. So with experience it is possible to check they match. A 1940s style valve label in a 1960s box is an obvious give-away it is the old valve.