this listing is for a NOS matched pair of the extremely rare Cossor 53KU (GZ37, CV378) with black base & black anode plate.tubes have the "K" factory code & were made in the UK in the 1940s or early 1950s. they are considered superior to the later Cossor 53KU with brown base & grey anode plate. 2 pairs aval. (ie. 4 tubes in total).
price for a pair: $800; price for a quad: $1500. no shorts, leakage or gas. tubes were tested by a reputable local tube store in April 2014 with a highly regarded [AVO VCM 163 tube tester]. test results at the position of 120 mA: [tube 1: 92/88] - [tube 2: 90/90] - [tube 3: 90/90] - [tube 4: 90/90] (note: good/strong tube will test around 62/74)
Paypal +4%.
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