Free tubes - 6550 and 5881 - Audio Research and International ServicemasterThese two tubes came in a lot of tubes I bought from an audio repair shop that went out of business. They were described as not having been used and they test really well. I don't have a use for them and rather than throw them away would pass them on to someone who can use them for the cost of postage, $5. Transconductance numbers on a calibrated Triplett Tube Analyzer 3444 are:
5881 - 4600 where 4700 is considered new --
6550 - 6200 where 6000 is considered new Label for the 5881 says International Servicemaster, USSR Label for the 6550 says Audio Research - Made in China
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