6su7gty 6188 tung-sol tube preamp tubes black round plate pair test strong
two tubes = 2 pieces = two valves type 6su7gty 6188 tung-sol
tested on tube tester TV7D/U
test results as follow
tube 1 = 40 & 48 code 3227-52
tube 2 = 44 & 44 code 322403-3
(reference good at 30 & 30)
brown base & round plate on both tubes
box 174