Neumann U-67 tests
These simple, unflattering audio samples demonstrate how different a vacuum tube can make a capsule sound.  In both tests, the mics were set to Cardioid pattern, no pad or roll-off.  The mics faced each other vertically so their capsules met.  I was about 10-inches from the mics.

U-67 "stereo" test-2: A pair of vintage U-67s. 

• The left mic has a modern k67 / k870 capsule with a vintage EF-86 vacuum tube
• the right mic has its original k67 capsule with a subminiature 5703 tube

Left-Right AH test-2: Mono Loop from the raw stereo recording test-2

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U-67 "stereo" test-4: A pair of vintage U-67s. 

• The left mic has a modern k67 / k870 capsule with a vintage EF-86 vacuum tube
• the right mic has its original k67 capsule with a subminiature "previously enjoyed" AC-701 tube as used in the M269 (Europeon Broadcast) version

Left-Right AH test-4: Mono Loop from the raw stereo recording test-4