I know this thread's a couple of months old, and that I might be inviting all kinds of criticism and nay-saying, but regardless, I can't resist throwing in my 2c-worth.
I'm the designer & builder of the Humphrey Amp mentioned above. It took over a year of full-time 7-day weeks to finalize the design & testing (I might be slow, but I'm big
First, I'll point out some obvious negatives, which really isn't good marketing practice - but I'm not marketing here, just explaining why I do what I do, so I guess it's ok.
1* Cost - yup, tube amps are more expensive than solid-state in general, and as mine are hand-built starting from raw lumber, and hand-wired, they are even more expensive - but they're certainly not targeted at the general market.
A typical solid-state amp can be made with a bill-of-materials total cost that is less than the cost of a pair of quality EL84's
Don't get me wrong - there's some fine s.s. amps out there and the fact that they CAN be made at low-cost and in high volume gives a lot of folks access to good gear.
2* Weight - yup, a Humphrey Amp weighs about 37lbs, depending on the wood used. We do need some hefty transformers. Actually more hefty than those used in electric guitar tube amps (don't want to saturate the xformer in an acoustic amp).
Also - we use a very heavy hi-fi class 10" speaker and brick of a horn-tweeter (all for good reasons)
3* Reliability. Depends what you're doing with it really. Tubes do wear out over time, but it depends largely on the voltage supply and how long they're played. My Marshall amp drives the EL84's with more than 420V (they're spec'ed for 300V) and after 5 years I'm thinking it's time for new tubes. I just use it for personal playing though - not gigging every night.
A Humphrey Amp using high quality JJ EL84's, running at much lower voltages, would run for many years before the sound degraded - unless you ride it hard & put it up wet every night of the week, of course.
There's actually fewer components & connections in a well-designed tube amp, so the reliability is inherently 'better' from the get-go.
It depends on a lot of factors though, and I'm not saying S.S. is inherently unreliable.
If I were to play the most important gig of my life & could choose only one amp, it would certainly be a (good) tube amp.
Okay - the positive stuff
1* I think it was Rollie that pointed out that some of the finest hi-fi amps in the world use vacuum tubes, so I'll not repeat what he said already. He's right, but I'd say that MOST of them use tubes. There's reasons for that.
We use a similar design methodology in our acoustic amp - it's all about the signal quality. In an electric guitar tube amp, everything about the design contributes to shaping, coloring and distorting the sound in ways that are pleasing to our ears. Understanding those things means that we can avoid the stuff that would be considered nasty for acoustic guitars, while still benefiting from the acoustic qualities that only tubes can deliver.
As Edward said . . . " . . The "correct" tube amp for the acoustic guitarist has to be designed thusly from the get-go, . . . "
Well said.
Add some secret sauce in the cabinet/speaker design and you have an amp that will cause you to pick up and play your guitar for longer, and more frequently (that's what my customers tell me).
Because it's not cheap to make, we figured it needed to bring as much to the table in aesthetic appeal as it does in sound quality, giving it some 'collectability' value, like one of the fine guitars it would be married to.
Like I said - I know it's not everyone's ideal, so don't knock us for going out on a limb with what we believe is solid product that meets an unmet need (yes, it's a niche market, but we're happy to serve it).
The interest is growing rapidly, I'm happy to say, and we're totally pumped at the reaction we get from folks that try/buy them.
There's a really nice video of Al Petteway doing a demo if you'd like to check it out.
http://www.youtube.com/watch?v=k4Wm0nl1tWk
Hopefully, this late night rambling will be received in the spirit in which it was given. I'm just offering a perspective & an explanation for why there's yet another piece of cool gear available for ACOUSTIC guitar enthusiasts. Maybe some of what I said is helpful in some way - I hope so. I don't intend to engage in arguments or respond to slams - but I'd sure welcome any good questions or fair comments.
Thanks!
Gerry Humphrey