Does anyone know of or have a guide that references replacements for known tubes? I have inherited a serviceman's case with about 150 tubes. While some are listed as 6L6, 12ay7, etc., others are completely foreign but size, shape and pin outs are identical to "known" types. I have dozens from ITT, GE, Lindal, RCA that have what I am assuming is their designation for the same or similar tube, for example a 12ax7. Several have the equivalent written on the side of the box. I've searched Google but most of the Tube types don't return any hits. Any help would be appreciated.