Really enjoying this discussion as Nat Magma Ms are on order for my system.
So, in addition to now wondering about these NAT Symbiosis New - first I've heard of these, gotta ask Mike, I'm also a bit concerned/quesitoning the approach that Nat uses to bias and manage tube life in his amps.
To be specific, the Nat amps auto bias, which I imagine is a fine approach (I'm no electrical engineer so can't comment on the pros nor cons of auto biasing vs the simpler resister and manual adjust approach). However, per a rather extensive email exchange with Dejan and discussions with Mike, the Nat amps do not indicate when the tube can no longer be biased within the target range. Of "concern" is that Dejan says the amp will continue to operate when the tube can no longer be biased within the target range.
Unlike many other tube amp mfgrs, Nat does not provide a ready means for measuring the bias voltage, nor an idiot light (eg red led) indicating the tube needs to be replaced - think the oil low light in a car. Experience with many tubes over the years clearly demonstrates that tubes do indeed age out and good new tubes can be a rather pleasant surprise.
Dejan's response to my concerns is that (1) the tubes have a long life because the design does not work the tubes hard at all, and (2) worn out tubes sound like crap. Well, while both statements are true, my rebuttal is (1) most tubes have a long life, some don't, and (2) I don't want to wait until I realize the system is sounding like crap. Importantly, tube "wear" is gradual, it is not a binary affair (barring failure of course). So, like the frog in boiling water or tire wear on your car (yup, another automotive analogy) we, or at least me, get accustumed to the gradual performance decline until....
Given all the time and money and emotion in this nutty hobby, I'd much rather know the status of the tubes in play. A means to measure voltage or an idiot light would alleviate that nagging wonder if the tubes are toast.
So, while I remain quite excited to put the Magma M into my system, its also frustrating to now learn that there is literally no way to know if the Nat tubes are operating at optimum - I'm begining to quesiton my decision and call off the purchase.
Thoughts? What am I missing here?