This new old stock-testing Matched Pair DuMont 6V6GT Gray Glass Black Plate output tubes was tested on our Maxi-Matcher 2 for shorts, gas and transconductance. There were no shorts or gas. Transconductance measured: Tube One: 20.2 milliamps / 2420 micromhos (Unbranded base with RCA codes 035 274 [274 is RCA EIA code]; 6V6GT on glass) Tube Two: 18.9 / 2230 (DuMont-branded stenciled on base with codes 4-22 274 [274 is RCA EIA code]; 6V6GT on glass) Measured with 400 volts on the plates and a bias of -36 volts. New US-made 6V6s typically test with plate current from the mid teens to mid 30s with transconductance from 2200 micromhos or so. (NOTE: Newly manufactured 6V6s also typically test from the mid-teens to mid-30s with transconductance from 3000 micromhos; because of the massive variety of this tube type and differences between new-production Eurasian 6V6s and older American varieties, readings such as this are common). Pair have black plates, gray glass, and are tight on bases with no debris or rattling. The pair sound tested outstanding in our shop amplifier (see pics). These are RCA-made tubes; 274 is the EIA code for RCA. Checkout other tubes in my store for your equipment needs. Shipping is USPS Ground Advantage with tracking in the United States. International sales shipping via International Shipping Program. Package weighs ten (10) ounces. Combined shipping always welcome on multiple orders. 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.