What do you see as the downside of tubes?

Regarding the comment by Markwatkiss about supposed fairy tales, high quality output transformers are mandatory (as are hefty power supplies) for controlling the woofers in the typical audiophile speaker featuring a 4 Ohm or less load in the bass, and they are extremely expensive. I am not aware of any tube amp that retails for less than $10k that can properly control the woofers of such speakers assuming a normal listening room and average program material.

Ralph (Atmasphere): I agree. I have owned auto-biasing VAC Renaissance 140 monoblocks (sixteen 300-B's) or a VAC 70/70 (eight 300-B's) for almost nine years - they have been completely trouble-free. Having an amp that, if I may quote you, "is designed properly" is the key - cheap tube amps do not play in your league.

How do you reliably diagnose the bad or failing tubes for replacement when an amp has so many tubes in use?

Loose bass, forward midrange, bright glassy upper mids/lower highs, rolled off upper highs. Variable performance. Unreliable. High maintance. Difficult to get replacement parts. When they break, they offer the potential to break other links in the system. Excessive heat. Potential burns to children, pets and others. Can cause fires. Requires more care in placement. Limited to use with high impedance speakers. High cost per Watt. Greater sensitivity to speaker cables. Sensitive to vibrations.

Every time I come back there's more. Looks like I started a small avalanche here :)

I shall take a look at the amps mentioned in the thread though so far I haven't chamged my mind. The only thing I don't like so much is the price of tubes. But at least it seems one can get them. Can't say that about ammo for my target gun (hmmm, yeah, sometimes I like things that make boom.

The other thing that does seem to crystalize is that there is somewhat of a potential for damage to the speakers if a tube says goodby in the shape of a wee supernova. Is there anything that can be done to prevent any downstream damage like additional fuses?

Well, thanks again and I shall check back later on.

Nice thread and some very good points both pro and con. I like the sound of tube amp and the ease of a good sounding SS amp, I use both, but all of my SS amps lean toward the sound of tube amp. Since I also own the Mastersound 300B SE I am going to address your questions with this amp in mind. The Mastersound only has 6 tubes, 2 of which are the 300Bs so heat is not really much of an issue, compared to most tube amps this one runs pretty cool. My Mastersound amp is the higher output version which uses either the 32B or 300BXLS tubes and yes these tubes are quite expensive, probably around $625 for a pair of 300BXLS tubes, the 32B tubes cost much more. However, new regular 300B tubes can be found for around $150 for EH to around $350 for a pair of really nice Full Music Mesh Plates all the way up to very expensive Western Electrics with various price points all the way up. The other tubes, 5687s and 12au7s are very inexpensive, so overall tube replacement is not all that expensive or much of an issue.
Biasing the 300Bs will require a meter but those are cheap and biasing the output tubes only takes a few minutes. Once the tubes settle in I only need to check the bias about once a month and rarely do I have to make any adjustments. So overall the downside to this particular amp is very small in relation to the sound it produces.