This is a microphonic tube, it needs to be replaced. Modern tubes, specially chinesse ones, are more prone to microphonics than older ones.
So avoid China made tubes when you replace it with a fresh one. Better with NOS, but Sovtek, Tesla or Electro-Harmonix replacements will do a nice job.
I never got a decent bass sound from a D112 alone on live scenarios. I tend to combine it with a more midrangy/thicker mic, usually an Audix OM3 with more... let's say "accurate" results. But most of the times I usually go with just the Audix. I only use the AKG when I really need to go that low ...