Which tubes best for Magnum Dynalab 106t tuner?

Those low output type tubes 6DJ8/6922 should last for many years without replacement. You should take a look at some vintage GE or Sylvania tubes. You can’t beat those vintage tubes. I use them in my line stage and phono preamp and have never had any failure after about 10 years of use!

The Telefunken tubes I have been using for years always gone bad within a year. How long should tubes last in the MD106t tuners?

When I had my Magnum 102 T tuner, I used NOS Mullard tubes.  The sound was what I was looking for, but they went microphonic within 8 months. I purchased them from Uncle Kevvy at Upscale and they were rated as platinum( their best tubes).  At 8 months, Upscale wouldn’t do anything for me.  It was a very expensive lesson.  I am hearing the Mullard reissues are quite nice.