What are NOS valves?
NOS stands for new old stock. These are valves that are unused, hence “new”, but are no longer currently in production, hence “old stock”. Interest in NOS valves started in the 1980s when most Western countries were winding down their valve production. Some valves such as the KT66 and GZ34 went out of production completely, and the general consensus was that the valves being produced in the old Eastern block, or China were of poor quality. There is much truth in this view; however this is not always completely fair as some companies were often branding “equivalent” current production valves as something they weren’t, and using them inappropriately. An example of this is the Russian 6P3S, which we have seen labelled as 6L6-GC, 6V6-HD or KT66, when in fact it is none of these. Due to dwindling supply, the price of many NOS valves has risen dramatically, with the price of a quad of matched NOS GEC KT66s, if you can find one, now in the eye-watering category. Fortunately, there are an ever
