Vacuuum tube digital circuits (50 year rule)

This is true if the mix is completely random with a majority of hopeless TV series string types or the tubes are not trusted to be NOS (_always_ check the tubes in the boxes - often the old TV guys would reuse old boxes for used tubes). Tim is correct - any pile that fails these two tests are pretty much worthless. The boxes are woth more than the tubes (no joke). If, however, the tubes are known to be new old stock AND are reasonably useful (for US receiving types, look for 1, 6 and 12 volt types), a fair buying price is quite a bit more than pennies per tube. It should be noted that nearly all computer rated tubes have RMA-EIA numbers. There are a LOT of them, especially the 12AU7oids, so you need to know which ones are the good ones. Just because it looks like a 12AU7 and has a four digit number does not mean it is computer (or audio) rated - many of the sub-species are rated for other uses - mobile, ruggedness, and so forth. The best way to decode all the number is to just get a copy of Ludwell Sibley's TUBE LORE. I do not know if anyone here collects computer rated tubes, but I have an extra 1680 available for trade. This is a very early computer rated 6BE6 (the thing is also branded 6BE6), and is extremely difficult to find, as it was obsoleted very quickly by the 5915. -- Will