I have 4 sunn amps. My main amp is a first gen model T. I went on a sunn buying spree and kind of want to get down to just the model T and one of my solid state heads to have as a backup amp. I have a silver concert lead, a red knob concert lead, and a beta lead. They are all heads and all minty condition. All of them work flawlessly. I love the betas distortion but prefer the concerts clean sound. Since it will be a seldom used backup, I guess I want to keep the one that will be easiest to keep running. Which of these will be the easiest in the future for a tech to service? I know the beta has a logic chip or something that is nearly obsolete. Would one of the concerts be a better choice as far as parts availability? Do the concerts have any rare hard to find components? Which one of these would you sunn fanatics keep?