Which tubes to replace Threshold SA/1 monos

I am currently using the Thresholds with Magnepan 3.6s (I may potentially upgrade to the 20.1s in the future) and would like to try some tube amps. Anyone made a succesful change from transitors to tubes with the larger Maggies? Thanks.

The SA/1's were one of the all time classic amps ever made . Tube or solid state. In my opinion you would be making a big mistake switching to tubes, especially with those speakers. I would keep what you have and enjoy the music.
Its a case of boredom. It will pass. You have amps that are benchmark products, even today.
I sold a pair of these last year... I regret it.
Sweet, huge sound.

Aesthetix Atlas Mono Blocks would have a more friendly input imp and match well with your Aesthetix Callisto pre amp
Best Johnnyr
You might want to take a look at Audiovalve Challanger lineup;I am driving soundlab m2's with excellant results using their Challanger 180 monoblocks;these amps will run el34,6550 and kt88's. They are class A and have balanced/rca inputs;excellant build quality and good worksmanship as well.
Thanks for the feedback. I put the First Sound back into my system over the weekend with great results and don't plan on making any chages for now.