I know this is an old thread, but I recently bought a DT50 112 online as the price was fantastic. It did have quite a bit of white noise, especially on the British Chime configuration, class A, no negative feedback loop. I found that channel unplayable. Read this thread and got around to finally changing the 12AX7s (Russian Electroharmonix) to basic Slovakian JJs ECC83s (Tesla remake). Made a nice difference - won't say it was a huge difference, but brought the noise to a reasonable level. I've attached a picture showing the before and after noise level taken with my iphone - the impact is clear.