Tested on an AVO valve tester, with results shown below. These are badged ‘Marconi’, but have the acid etched date codes of Mullard's Blackburn factory which clearly identifies it as a Mullard tube.
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VALVE TUBE JOB LOT MARKINGS ARE RUBBED BUT IT LOOKS LIKE A CV4004. EF86 AND A 12AT7 BUT MARKINGS ARE RUBBED
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All tubes are tested with the Audiophile in mind for SHORTS, GAS, MUTUAL CONDUCTANCE and NOISE (large tube lots are not tested for noise). AT1000 TESTs as NOS. VALVO EF86 (6267) Power Tube (Single). Here are the desired target numbers for a EF86.
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They preferred the GEC CV4085 over the Mullard CV2901 as the heater wire in the CV4085 was wound as a double helix with a specified number of turns and pitch as specified by the MOD to minimise the external AC hum.
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GEC, British Made. NOS, Supplied in White Box.
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MULLARD BLACKBURN FACTORY " B " CODES ETCHED INTO THE GLASS. BOTH VALVES TESTS 100% STRONG ON MY B&K 747 AND HICKOK TV-7 TUBE TESTERS.
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All tubes are tested with the Audiophile in mind for SHORTS, GAS, MUTUAL CONDUCTANCE and NOISE (large tube lots are not tested for noise). AT1000 TESTs as NOS. Here are the desired target numbers for a EF86.
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RARE: 8Yn Production - Diamond Mark on Bottom. All tubes are tested with the Audiophile in mind for SHORTS, GAS, MUTUAL CONDUCTANCE and NOISE (large tube lots are not tested for noise). AT1000 TESTs as NOS.
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