Both tubes have been tested on an AVO valve tester. Results show strong performance with good transconductance, consistent across both triode sections. These are badged ‘Marconi’, but have the acid etched date codes of Mullard's Blackburn factory which clearly identify them as Mullard tubes.
eBay
ECC83 / 12AX7. TESTS 100%.AS GOOD OR BETTER THAN NEW TUBE. 100%. PRICE IS FOR ONE PIECE. ( 1 Tube ).
eBay
Here is one USED ECC83 (=12AX7) in original box, made by Mullard in Blackburn, England. There is a bit of a Mullard code: B9G. The valve is in very clean condition, but the printing is slightly less than perfect.
eBay
MULLARD ECC83 VALVE TUBE BRITISH GOOD QUALITY PLEASE LOOK AT PICTURES
eBay
Matched pair of Mullard ECC83's. Short ribbed plate, one white and one yellow print. White print manufacturer code I61 B1L2 - 1st iteration, Blackburn plant, 2nd week of Dec 1961.
eBay
ECC83 / 12AX7. These tubes test less than 100% on one or both anodes but are perfectly good and have plenty of life left in them. PRICE IS FOR ONE PIECE. ( 1 Tube ). 75 - 99 %.
eBay
A used 14mm short-plate ECC83 (12AX7) tube in good condition and in full working order. Plate Current: ia (mA) 1.2 1.2 1.2. Actual Readings.
eBay
It’s been said that the Mullard sound can be most likened to a warm British jacket of the finest tweed. And I like how Mullard tubes sound, too. Enticingly intimate and warm, almost sweetly so, it’s always a close, handsy dance when listening to a Mullard.
eBay