In reference to earlier posts, I just replaced the stock tubes in my Unico with Mazda chrome plates (platinum) from upscale audio. They recommended two different ones based on my desire for a bit more openness and high frequency extension. The other was the radio technique. The Mazda's have made a stunning change in the sound of the Unico compared to my expectations. So much more detail and HF extension. I was wondering how a manufacturer could ever voice an amp at the design stage with this much variability available with different tubes? I guess manufacturers may use what is readily available and have to hit a price point. The Mazda's were $80 for the pair. I guess that would significantly have changed the selling price etc, etc. Anyway, I am super happy and can't wait to get home to listen to my new amp!