A nice tube that will outperform any current production 6550. Matched to within 5 percent. An excellent 6550 that is beginning to vanish as the Tung Sol tubes soar in price. These tubes were hand selected for medical equality so they are dead quiet. These were all tested on a calibrated tv7 military tube tester where a score of 62 is new and 44 is minimal good. All tubes range from no lower than 58 up to 64. Great sounding 6550 tubes and they all have the same plate structure with the double solid pan getters at the top and one side getter. These tubes were made in the late 60?s until the early 70?s. 62 and minimum good is 44 all tubes test in the high 50s (58,59) to low 60s (up to 64).They are great tubes.They were pulled from medical equipment and were hand selected for said equipment due to the requirement that they be dead quiet. Essentially they test new or as close as you can get to it and gently burned in... picture shown reveals beautiful silver flashing.
Check the going prices at:
https://www.tubeworld.com/6550.htm and you'll see the same tubes go for $300 a pair, mine will go for $300 a quad.
Paypal accepted and buyer pays Paypal fees and shipping which will be $6 per quad.
I read a article in VTV Issue #6 (VTV6) titled "KT88&6550 The Power Kings" by Eric Barber. It is a interesting article giving some history about development of these tubes. By the 1960's these tubes had set the standard for power amplification. So it was inevitable that other makers would introduce their own versions. GE came out with the straight sided 6550A in 1971. It was called the 6550A, because of the introduction of a exotic 5-ply metal plate material manufactured by Texas Instruments. This metal, produced by cladding a copper and iron core with aluminum outer layers using explosives, made for a more reliable tube with greater bias stability. The clad metal was better a dissipating plate heat, and thus it lessened plate and grid emission and reduced hot spots on the plate.
Understand that these tubes will outlast any brand new 6550/KT88 by miles. They don't make tubes to last like they did back then not to mention tone that is candy for the ears. The only tubes that beat them are NOS G.E.C. KT 88s or NOS Tung Sol 6550 Black Plates and good luck finding them and plan to pay exhorbitant prices if you can find them.
