These are excellent examples of the 6201 (more commonly known as 12AT7) tubes used in US government computers from 1939-1963. They are in pristine condition and have incredibly well matched triodes (= or less than 1%) that are well beyond what is expected from them in terms of gain. They were only ever used in laboratory conditions and are perfect in every way. Supplied in plain white boxes as per the photo. FREE SHIPPING!!! Discounts on multiples!!! 50 pieces available at time of listing. Message me for details.