This new old stock-testing RCA Matched Pair 6L6GB output tubes was tested on our Maxi Matcher 2 for shorts, gas and transconductance . There were no shorts or gas. Transconductance measured: Tube One: 20.6 milliamps / 2100 micromhos (RCA logo stenciled on base with code 57-1__; 6L6GB on glass) Tube Two: 20.4 / 2210 (Unbranded yet RCA made, RCA EIA code stenciled on base 57-__ 274) Tubes tested with 400 volts on the plates and a bias of -48 volts. New old stock US-made 6L6s typically test with plate current from the mid-teens to mid 30s with transconductance from around 2200 micromhos. Tube Two was also tested in our Jackson 648, it tested 99. Good range is from 70-130; this tube test 99%. Tubes have a black plate, dual bottom D getters, a top radiator for cooler operation and longer tube life, each tube has two top mica scrubbers for increased resistance to vibration and are tight on base with no debris or rattling sounds. Sound tested outstanding in our Musical Paradise shop amp (see pics). Make sure you amplifier is rated for 6L6GB tubes. Tubes ship via United States Postal Service (USPS) Ground Advantage with tracking for domestic U.S. sale; Priority Mail is an option if you desire quicker delivery. International orders ship via International Shipping. Package weighs twelve ounces (12 oz). Please view my store for other varieties of tubes. Combined shipping always welcomed. TUBES ARE GUARANTEED GOOD AND IN WORKING ORDER AT SHIPMENT. TRANSIT VIA POST CAN DAMAGE TUBES. THIS IS NO FAULT OF OURS BUT THE THIRD PARTY ENTITY THAT IS DELIVERING ITEM(S) TO YOU, I.E, USPS, UPS, FEDEX, YOUR NATIONAL CARRIER IF INTERNATIONAL, ETC. PLEASE INSURE THEM! WE CANNOT GUARANTEE FAILURES ON YOUR EQUIPMENT AFTER POWER UP AS THERE IS NO WAY TO ASCERTAIN HOW TUBES WILL INTERACT WITH YOUR ELECTRONICS; NOR IS THERE A WAY TO DETERMINE WHETHER THEY MAY HAVE FATAL FLAWS IN TUBES THEMSELVES! THESE ARE USED VACUUM TUBES AND TIME MAY HAVE TAKEN A TOLL ON THEM OVER THE MANY YEARS SINCE THEY WERE MANUFACTURED. WE CAN ONLY TEST FOR THE PARAMETERS MENTIONED ABOVE IN ONE OR MORE OF THE FOLLOWING EQUIPMENT WE USE FOR MEASURING: TV-7/U, JACKSON 648 MAXI MATCHER 2.