Never Owned a Tube Amp and Want Advice


Hi All, 

I have never owned a tube amplifier before and am planning to purchase one with a minimum of 50 watts per channel to mate with 8 ohm 88 dbl speakers.

My hope is experienced audiogoners will share their expertise regarding how to approach this. While I realize listening is the best way to learn about sound and compatibility; I want to learn a better understanding about brands with less maintenance and longer tube life, how to decide between mono or stereo,can a newbie play with bias or is auto biasing a better first choice, etc.

I would also appreciate what to look for in selecting a used tube amp to identify one that might be in need of repair. For example, with solid state depending on the brand, capacitor replacement can be more of a concern. Any advice on what to look out for or ask about with used tube amps would be appreciated.

A big question I have is how to understand the relationship between power tubes like E34's, 120.s, etc. and, I guess the driver? tubes like 12au7's and 12at7's. That  is to ask which is more critical to the overall sound of the amp? FWIW, I routinely tube roll with my preamps.  

I 've read through a number of threads but maybe someone can point me to good ones I may have missed. 

Thanks for listening,

Dsper
dsper
EL34 are a bit warmer than KT88, which are very slightly warmer than 6550C. But these are gross generalizations, and its a mistake to focus on the tubes. In reality the transformers are equally as important, as are the quality of caps, power supply diodes, and the overall quality of construction. In other words tube amps are just like everything else. To focus on the tubes without considering transformers is as bad as to focus on the drivers while ignoring the speaker cabinet.

Honestly, I know you want a tube amp but my advice is forget that until you're into some more tube-friendly speakers. 90dB can work, 95dB is a lot better, and 98 or more is beautiful. Because while tube watts are greater than solid state watts still you are much, much more likely to find a really good sounding tube amp in the 50-60 watts or under than 100 watts or greater.

Realize that because dB is logarithmic doubling power from 50 to 100 only gives you 3dB. My last speakers Talon Khorus at 90 dB were pushing my 50 and 60 watt tube amps hard when playing loud. But if I were to go to a 100 watt or greater amp it wouldn't be worth it for all that money (and long term tube expense) for just 3dB. You're 2dB less. You are screwed. No one else here will tell you this cold hard reality.  

With speakers 95dB or greater though, now you can take your pick of really great amps that will absolutely kill anything SS and play nice and loud, and with even better bass. You experience this you will forevermore roll your eyes at all the rubes mindlessly repeating the SS bass mantra. Right. As if.

So speakers first, then amp.
OP; what speakers will you be using?
Impedance will determine how well an amp drives the speaker; ie, a speaker with an impedance curve that stays in the 8ohm range will be easy to drive. The 88dB sensitivity may be on the low side but is less important if the speakers have an easy load to drive.
If you need high SPL’s in a large room, higher sensitivity speakers are required.
So, need to know more than the nominal impedance spec, although 50 to 60wpc may be fine.

The tube which has the most impact sonically is the gain stage input tube, often a 12AX7. Power tubes will provide the timber or tone of music; warm or neutral, bass and treble extension.
Transformers play a very important role in amp implementation. They have a sonic signature and the amount and quality of current delivered will affect speaker performance.



you are asking a question that takes a short book to properly answer

i suggest you do a search for something like ’hifi tube amp basics’ on youtube, and watch several entries that pop up - you will educate yourself faster than reading peoples' snippets here
FWIW, I have Quicksilver 60wpc monoblock tube amps and at first I thought I had to have high sensitivity speakers. I did try some at 92, 93 db and they had an easier time than speakers I tried at 87 and 88 db but I have to say I found that the Monos were perfectly fine powering speakers as low as 87db. They sounded delightful and not at all underpowered. I do suspect that a lower powered tube amp might have had more trouble, but my QS has a honking transformer and easily controls those lower db speakers — which I liked better. Impedance, as lowrider57 said is very important. I had 92 db Focals which had a bad dip in the 4 and sub-4 ohm region, and that proved a problem with the sound, in my setup.

As others here have said, this is a huge topic, and I will admit, I am a newbie. So all I am saying is that I *thought* I had to rule speakers "under 90 db" out of consideration -- and I found that proved false by actual experimentation. Also worth noting: in my space, I only need to play speakers about 8 feet away, at about 80db volume to sound good an loud.
While speaker sensitivity is important when considering tube amp matching, you should place as much weight, if not more, on impedance (how easy the speaker is to drive).  One reason Joseph Audio Perspectives (eg) work so well with many tube amps is because they're 8 ohm speakers that never dip below 5.5 ohms.  Yet their sensitivity is only around 84dB.  Tube amps 50w and higher should work well with them.
The speakers in question are Tyler Acoustics. Tyler advised me they are 8 ohm 88 dbl and should not dip below 6 ohms. 
@dsper 
You should check with Tyler, but a 50-60 wpc push pull amp should be fine with those speakers.

My speakers are 90dB, 8 ohm nominal. The impedance curve is pretty flat at 8 ohms and I use a 30wpc dual-mono Atma-sphere amp. Wonderful sound.

Post removed 
That's great info @tvad .
Which leads me to question, how large is the OP's listening room?

Which leads me to question, how large is the OP's listening room? 
Listening room is 25 X 15 X 9.  Due to room logistics, speakers are two feet from the front wall and the speakers are about 10 feet from listening position; thus half the room is behind the listening position. 


I suggest reading Robert Harley’s book "The Complete Guide to High End Audio", paying particular attention to the chapters on amplification.
Good reminder to take another look at it. Thanks!

Selecting tubes and tube amps to suit your needs is very subjective, plus there are a bunch of variables that are unique to each situation. Pick a well regarded amp circuit as a starting point, and get your feet wet...you can taylor the types and brands from there as needed.

I’m running two Dyna/VTA ST70s in a vertical passive bi-amp configuration, which allows me to use different tubes on the woofer channels than those on the tweeter channels. They’re all EL34s, but there are differences between brands, and it’s fun to experiment with them. My stock driver tubes are 12AU7, but I recently opted for 12BH7s in the more critical positions...I love those.

My amps have a manual bias that’s really fairly easy to do, and once set, they don’t drift much. No worries if you can use a voltmeter.

I’m driving speakers of average 89db efficiency. I can run the amps in triode mode at 20wpc, or ultralinear at 35wpc. The vast majority of the times I opt for the clarity of triode mode, and almost never feel the need for more power or more volume. There’s so much room ambience, inner detail, and dynamic contrasts that I don’t feel the need to reach ear bleed levels anymore ....100db is more than enough to annoy my wife! Love the tubes, and will likely never give them up because of the glimpse into the studio that they offer. Good luck!


The speakers in question are Tyler Acoustics. Tyler advised me they are 8 ohm 88 dbl and should not dip below 6 ohms.
@
In terms of impedance this speaker is an easy load (which is good regardless of what kind of amp you have, but with tubes this is particularly helpful). The only issue is whether 50-60 watts is enough power. What are you playing them with now?



Even if you don't have the opportunity to audition a wide array of amplifiers in your home, you should at least make the effort to hear one or two with your speakers to get some idea of whether tubes are really for you.  I've heard Tylers (don't know the model) with some medium and lower powered tube amps, and I thought they played well together, but, that is by my standards, taste and listening practice (I don't listen at high volume levels). Only you can decide how loud the amps must play, how much bass and bass control you demand, how important is the ability to play softly and still sound reasonably balanced and exciting (tubes are generally good in that regard), and a host of other considerations.

For my particular taste, I am not a big fan of high-powered tube amps; if something requires more than 50 watts, I am inclined to look at solid state even though most solid state amps sound slightly lifeless to me, particularly at lower volume levels.  I generally find higher powered tube amps to sound brittle and a little bit harsh.

If you don't demand ultra deep and punchy bass and rock concert volume levels, I think you could find a tube amp that would make you happy, assuming, that is, that the Tyler speakers are a reasonably easy load to drive.  I've heard many speakers with a lower efficiency rating than 88 db/w that worked well with 50 watts or less.

The only issue is whether 50-60 watts is enough power. What are you playing them with now?

I am currently using my McCormack DNA 500 (which is a necessity with my Thiel CS5's) to power the Tylers.

Have been listening to "The Essential Jaco Pastorius" and then some George Thorogood.

The decibel reading at my chair is averaging 80 dbl with peaks at 92 dbl.

I do not need it any louder than that and generally listen at lower levels. 

Dsper
You should check with Tyler, but a 50-60 wpc push pull amp should be fine with those speakers.
As I recollect prior discussions with Tyler, he indicated that he has customers using 50 watt tube amps but also mentions that he thinks 100 watts solid state is a good number to consider.

FWIW, I have also run a Coda CS (300 WPC) with them, just to see, but went back to the  DNA 500 because I hear more textural detail and pace.

Dsper 
Tube watts are NOT more powerful than SS watts, they simply can present distortion in a more pleasant way. I suggest a Black Ice (formerly Jolida) tube amp as they're well made, sound great, and inexpensive even when new. I owned a 502p amp and it served me well...great stuff.
What you will/may notice when a tube amp is driving a speaker with low impedance dips is an uneven frequency response, e.g. the speakers may sound "bright".

I think that is exactly what worries me about a tube amp. Can it cover the low frequency impedance dips.

With solid state, one can form, at least, a preliminary sorting by learning the  8/4/2 ohm and watts specs; but it does not seem to be that easy with tubes. A few tube amp suppliers claim a 2 ohm load capability but most of the websites I have reviewed are silent on this topic. 

Maybe I am worrying too much about it based on my Thiel CS5 experience.  

Thanks for listening,

Dsper
Post removed 
The decibel reading at my chair is averaging 80 dbl with peaks at 92 dbl.
@dsper

50 watts should be enough unless your room is really big.
Can it cover the low frequency impedance dips.
Our amps are some of the most sensitive of amps to load, and even they would be fine on a speaker like this. You’ve no worries about a dip 6 ohms with any tube amp made!
Interesting to read about the Tylers.  You don't  see much hype about them here.  They seem to be a good value speaker and tube amp friendly.   Got my attention.
A few tube amp suppliers claim a 2 ohm load capability but most of the websites I have reviewed are silent on this topic.

It depends on how the output transformer is configured at that load.   
Well, perhaps those low efficiency speakers will help you preserve your hearing longer in your life, avoid tinnitus, ... I never thought of it this way.

you can find much on the net, i.e. This site, scroll down some, says average Classical Concert is 90db, with momentary peaks of 120db.

http://www.audiodrom.net/en/as-we-see-it-tips-thoughts/74-realistic-volume-levels

this one, posted above, scroll down, shows sound level lessening by distance, IN OPEN SPACE

https://www.puiaudio.com/pages/speaker-power-and-distance

i.e. if you are 4 meters/13lf away, it is -12db. That is 4 meters FURTHER than 1 meter, so that is 5 meters/16lf away from face of speakers.

ignoring that the room’s surfaces will retain sound levels, or that there are two speakers: let’s do

some OPEN SPACE SINGLE SPEAKER math.

your speakers, 1 watt, 1 meter = 88db
sit 5m/16lf away -12db = 1w/5m/76db.
double the power in watts for each +3db sound level

to get to concert hall avg 91db, (5 doublings) math says you need 32wpc.
a 94db momentary peak will need 64wpc. (you mentioned 60wpc)
128wpc for 97db, keep doubling for each +3db peak

.........................................

Practically, the answers from people who have used low efficiency speakers with ____? wpc tube amps will give you the best indication, so tell us, or ask them:

room description
desired volume?
type of music, i.e. just loud peaks, or loud average?
length of listening sessions in time is also a big factor regarding hearing loss.


to get to concert hall avg 91db, (5 doublings) math says you need 32wpc.
a 94db momentary peak will need 64wpc. (you mentioned 60wpc)
The above explanation makes me think of another question, probably a dumb one. 

When I think of solid state, I understand that the continuous power rating is one thing and peak power supply is another.

My question is:

Is it true with tube amps that if an amp is rated at 60 wpc that is all you are going to get or do capacitors, power transformer, etc. come into play to allow higher peak power?

Thanks for listening,

Dsper


Most tube amps are "optimistically" rated.  That 60 watt tube amp might deliver that wattage at peak, but at 60 watts, it would be typically distorting quite a bit.  Tube amps simply do not do well in a numbers game.  

Because most tube amps are distorting quite a bit before reaching their "rated" output, a 60 watt amp should be considered more like a 30 watt amp.  But, even with your 88 db/w efficient speakers, you will mostly be operating below one watt of output anyway; only a few peaks might get close to 30 watts, and tube amps distort gracefully.

I think most people who are unfamiliar with tubes substantially overestimate how much power they will need.  Unless you have notoriously difficult to drive speakers, even modest tube amps can be made to work with your speakers.  If you have to keep the volume down a bit, that is just one of those compromises that one has to make with ANY piece of audio gear; none are perfect.

I suspect that the notion of "tube watts" being more powerful than solid state has to do with the subjective impression that good tube amps deliver--the sound is full, lively and engaging at substantially lower volume so one thinks the system is playing loud when it is not.
Everyone, I appreciate the input. Seems like I have to start listening and go from there!
I should have mentioned that you should also look at output transformerless (OTL) amps.  Atmasphere mentioned, above, the the Tylers are an easy, flat load.  That makes them a good candidate for an OTL amp.  Atmasphere, following forum rules, did not mention his own brand of OTL amps, so I will mention them as good candidates.  These amps sound very clear, immediate, lively and engaging.  For my taste, they are a touch lean (midrange on up being a bit more prominent than upper bass), but that is a matter of taste, and the good attributes of Atmasphere amps can be quite compelling.

For not crazy expensive amps, I like the Italian brand Synthesis, particularly the A40 and A100 models (the bigger chassis models of this brand are more reliable because they have less tendency to overheat).  Tonally, this brand leans toward the warmish side.  The same is true of Audio Note, another brand I like, but, most of their stuff is quite pricey.
When I think of solid state, I understand that the continuous power rating is one thing and peak power supply is another.

My question is:

Is it true with tube amps that if an amp is rated at 60 wpc that is all you are going to get or do capacitors, power transformer, etc. come into play to allow higher peak power?
Peak power is an early 1970s thing. All amplifiers today are rated at continuous power. 

Now 'peak power supply' as you put it might be a current rating that has to do with what happens when you short out the power supply, and might be stated in amps. This is really a statement of how much energy is stored in the supply (and how big the spark will be when you short it out) rather than anything to do with how much power the amp makes.

Most tube amps are "optimistically" rated. That 60 watt tube amp might deliver that wattage at peak, but at 60 watts, it would be typically distorting quite a bit. Tube amps simply do not do well in a numbers game.  
This has nothing to do with tube or solid state and has everything to do with how conservative the manufacturer is with their ratings. We rate our amplifiers for RMS power into an 8 ohm load and we rate them to not be clipping at that power level. Now there are different definitions used by several measuring organizations such as Stereophile, but clipping technically speaking is when you see the test sine wave signal getting a flattened top and bottom- as if someone 'clipped' the top and bottom of the waveform off with a pair of scissors. That is why its called 'clipping'. Any other definition is arbitrary.
  For my taste, they are a touch lean (midrange on up being a bit more prominent than upper bass), but that is a matter of taste, and the good attributes of Atmasphere amps can be quite compelling.

Being more load sensitive, this has far more to do with how the amplifier is dealing with the load rather than the actual character of the amp itself. If you have it on a proper load (and the Tyler appears to be an excellent example) its not at all lean. The bigger the OTL, the less of an issue this is, IOW smaller OTLs are more load sensitive.


Now @larryi made a  good comment about amplifier clipping- if you plan to use a solid state amp, my surmise is you'll need to have about 200 watts to do what a 50-60 watt tube amp will seem to do on this speaker, entirely because of the simple fact that tube amplifiers clip (overload) so much more gracefully than solid state. When a solid state amp breaks up, its instantly audible even if its only for a few milliseconds. But in the case of a tube amp this isn't always true. They can overload so gracefully that it may not be apparent until the amp is really heavily overloaded. IME its important that the amplifier have instantaneous overload recovery- this is very helpful in minimizing the audible artifacts when the amp is briefly overloaded. This is why tube amplifier power seems to carry more weight than solid state.


Here we go again with the statement that tube watts are greater than S.S. watts. This statement is patently false and should call into question anything this member says in the future. Also, I maintain that impedance is more important in the greater scheme of things than efficiency when considering speakers with tube amps. Higher impedance speakers allow one to consider OTL amps which are the best I have heard.
Here we go again with the statement that tube watts are greater than S.S. watts. This statement is patently false and should call into question anything this member says in the future.

Are you sure you want to go there? "This member" didn't state that tube watts are greater than SS. He provided a very good, comprehensive explanation. "This member" should know, he's been designing high-end tube amps for at least 30 years.



Yes, Ralph was talking about clipping characteristics of solid state vs tube amps.

If you aren't driving the amps into clipping, then the clipping issue really isn't one.

It appears that a well designed and built tube amp in the 50-60 wpc range will work quite well with the speakers of choice mentioned.  It is always good to try the amp in you home system to make a final determination.  

But, there are some quite nice tube amps out there in the 50-60 wpc range.

enjoy
I rarely if ever disagree with Ralph and find his amps among the best I have ever heard. It was millercarbon that made the statement which I questioned. BTW this isnt the first time miller has made this statement about tubed vs S.S. watts.

@dsper 
As you likely know very well, a McCormack DNA-500 is no slouch, quality build, big transformer, 500 watts, a capable amp - originally $7k retail as I recall.

+1 on 8ohm speaker impedance comments shared above in your favor.  

If I were in your shoes, having come from similar SS amps over multiple decades, and gone through multiple stereo tube amps, I'd recommend demoing at least equivalent cost or higher quality level tube amps compared to your DNA-500.  Otherwise you might end up disappointed and not really gain a proper perspective of the potential difference.  

Perhaps some nice mono tube amps with quality made [beefy sized] transformers that don't break a sweat [nor run hot] might grab your attention, and for your low level listening requirements.  

Many folks here can suggest a few good ones for consideration! :) 




 
@audition__audio 
I'm so sorry to snap at you as I did, your comments are completely justified. I too have reacted to the ridiculous and incorrect statements put forth by that member.
And Ralph's contribution to this forum have been invaluable, so much so, I own one of his masterpieces.

The same is true of Audio Note, another brand I like, but, most of their stuff is quite pricey.

Audio Note and Esoteric are out of my league pricewise; and I question if one needs to spend that much...but maybe that shows my ignorance 
Now 'peak power supply' as you put it might be a current rating that has to do with what happens when you short out the power supply, and might be stated in amps. This is really a statement of how much energy is stored in the supply (and how big the spark will be when you short it out) rather than anything to do with how much power the amp makes.
To be perfectly clear, energy stored in the supply is how an amp can handle an orchestral crescendo that would cause it to exceed its continuous power rating, correct?


Since this is a conversation about having enough power, what about going for a larger tube amp  like 100 wpc.

This assumes that the 60 wpc amp builder can build an equal quality 100 wpc amp.

While it might be waste of money, I would never have to worry, correct?




There are trade-offs, aside from cost, with going for more power.  With some brands of amps, the cheaper, lower-powered version sounds better when playing at modest volume level than the higher cost, higher priced brethren.  This can be the case with solid state too.  I tend to find higher powered tube amps to sound a little bit brittle and hard (harsh?) sounding.  But, it is still far better to get an amp compatible with your power requirements and accept the less significant trade-offs.

You need to hear these things for yourself.  It is hard to say what you will like and dislike and how you would value the particular attributes of any given amp type, never mind particular model.  If you can, listen to a modestly powered EL34 or EL84 amp (a popular tube in lower cost amps that sounds very good), a higher powered amp using KT 88 or KT120 or KT150 tubes, and an output transformerless amp, like the Atmasphere S-30 or M 60 amps.  Of the more common tube types, I am a big fan of the 6L6 tube, but, those put out less power than the other tube types I've mentioned.
Post removed 
To be perfectly clear, energy stored in the supply is how an amp can handle an orchestral crescendo that would cause it to exceed its continuous power rating, correct?
No. The extra energy is useful to reduce IMD at higher power levels. Essentially it allows the power supply to have less noise- and less noise in the power supply results in the lower IMD of the amp.
Since this is a conversation about having enough power, what about going for a larger tube amp like 100 wpc.
As you increase the power of most tube amps, the output transformer has to be able to handle that power and at the same time make bandwidth. The problem is this basically doesn't happen; with output transformers as you build progressively larger devices, bandwidth is increasingly more difficult to obtain. For decades, 60 watts was the 'sweet spot' for push-pull tube amps, where they could make the power and still have the bandwidth needed (5-100KHz). You may not think that bandwidth above 20KHz is important, but unless you have a great degree of feedback (above 35dB or so) that bandwidth is important to prevent phase shift which can cause issues with tonality and the soundstage presentation.


Another thing to think about is the simple fact that 100 watts is not a great deal of power over 60 watts insofar as the ear is concerned- its slightly less than 3dB which is barely louder to the ear. But a 100 watt amp might have other properties (assuming bandwidth isn't an issue) at lower power levels that could be in its favor. So its a mixed bag.

OTLs get around the bandwidth issue by getting rid of the output transformer, so that tradeoff does not exist in them when going to higher power levels- a 200 watt OTL can be as fast, dynamic and transparent as a smaller one.


A small tip that I didn't know coming from a SS background.

Don't run your new tube amp without a load attached as it can destroy the unit. You may be especially tempted to do so right when to get it as you would like to A/B it against your old SS equipment while keeping both at operating temperature.

Fortunately I got lucky and didn't destroy my Frankenstein 300bs when I did this many years ago.
Yes, tube amps are sort of the opposite of solid state when it comes to running with no load or accidentally shorting the speaker leads (big problem for solid state, no big deal with tube gear).  

Another helpful hint for someone auditioning with tubes for the first time:  If you turn off the tube amp to switch things up, wait a few minutes before turning it back on.  Quickly cycling from on to off to on again can cause some tube amps to misbehave.  I've heard some loud crackling and I have seen rectifiers put on a light show when that is done.

I have owned every type of tube amps out there 
key questions what are your speakers efficiency,
room size, kind of music , how loud spl level
as a Former Audiostore owner these are key .
SET is the most pure or direct signal then triode, pentode.
SET  typically is under 10 wpc, or under 20 in Parallel.
Class A triode ,pentode noticably more tactile and closer to live 
using No global feedback .vs ultralinear which uses feedback which = added distortion for best class A and deal IMO .
Ayon from Austria have several big advantages They are a pure 
class A design , their integrated amplifiers are excellent 
and USA tube  is offering great deals with things being slower then normal.I just bought another one.
the heart of a tube amp the transformers and Ayon use world class 
Lundahl , also no vibration distortion causing sheet metal,all machined aluminum , and trouble free most important tube biasing 
Ayon is the only one that uses a microprocessor to monitor voltage as well tube wear, if It finds a tube failure the amp blinks goes into mute and circuit disconnectsFor safety, In back screen will tell which tube to replace , shut down,   Replace tube, turn back on hold button in for 10 seconds it takes about 10 minutes and all tubes put in memory and running optimum ,once a month you recalibrate tubes,last longer and and optimum Sonic MA voltages. A bargain IMO
for all the precision vs  China specials ,ultralinear Cheap toroidal transformers ,and have the nerve to charge up to $5K.  C core transformers like Lundahl are recognized as the standard for a top
quality vacuum tube product.
IMO, the best quality of sound is from tube amp Single Ended 3-5 W with full range speakers more 92 dB , direct connected to outputs, without crossovers, that press the sound. I use 8 inch full range for 50-15000 Hz and 12 inch bass speaker for 30-50 Hz. I have also open buffle  with 12 inch full range Electro Voice, direct connected to my amp SE 2A3 RCA. The sound is with quality for a level higher than every Push Pull amp with big power, that never You will use. Stay away from EL34, 6L6, KT88, 6550....tubes with sharp sounding......that people uses for guitar amps. If You need more power, You can use SE GK71, GU 81 .....with power more 20-30 W.....
FWIW, here's the description of the 60 wpc amps from Quicksilver. Notice the comment about both being able to handle difficult speakers AND also having the finesse of a low powered amplifier. I've put some lovely KT77s in mine, and it's really does a delicate job with much of the acoustic I listen to, but has filled the room easily with orchestral stuff. Speakers are 87db, 8 ohm.

Via Quicksilver:
The new sixty watt amp retains the high damping factor and low distortion of the Horn Mono but with enough power to handle inefficient and difficult to drive speakers. The new power transformer has the same high grade core material as the output transformer. Also a new circuit increases the power tube bias at higher powers allowing the amp to have low distortion all the way up to clipping. At reduced powers this circuit gives the efficiency, finesse and delicacy of a low powered amplifier.

Power Output 60 watts into 4 or 8 ohms
Power Bandwidth 14 Hz to 70 KHz
Damping Factor 20
Input Sensitivity 1.2 volts
Input Impedance 100 Kohm
I.M. Distortion: less than 0.5% at 60 watts
Tube Complement two KT88, 1-12AX7, 1-12BH7
Power Consumption 100 watts at idle 200 watts at full power


As I've stated above, I am a fan of low-powered tube amps.  I own a pushpull 45 amp, a pushpull 349 amp and a parallel single-ended 2a3 amp.  I like the sound of all of them.  If forced to pick a favorite, it would be the pushpull 349 amp (5.5 watt), followed by the parallel single-ended 2a3 (6.5 watts).  The very best amps I've heard were both very exotic--one is a custom-made output transformerless amp and the other is a pushpull 252 amp (a tube similar to a 300b, but much rarer).  In other words, I would not say that any particular topology is superior to another--there are good examples of each tube amp type.
Don't run your new tube amp without a load attached as it can destroy the unit.
If the amp is of competent design, *as long as there is no signal at the input* this should be no worries. Our amps do not care about the input and output condition- they are unconditionally stable- you can even pull power tubes out while its playing and the amp acts as if nothing happened.

you can even pull power tubes out while its playing and the amp acts as if nothing happened

NOT RECOMMENDED... seriously

might be true for ralph's amps but this is something that is best NEVER to do
As long as this is going to be your first I have a couple of recommendations.  The Carver Crimson 275 is rated at 75 watts per.  It will run on 6550's, kt66, kt88, (supplied), and kt120's.  And the amp runs on a circuit that just allows the tubes to cruise along and allows the tubes to have a very long life.  You can put your hands directly on the power tubes on not get burned.  The drivers are 12 xx7 series, (I think 1 12ax7, and 2 12au7.  If you swap out these stock tubes to NOS you will have a giant killer that will drive just about any speaker you throw at it.  Auto bias and you can manually adjust bias to go more or less "tubey" sound.  And heres the kicker....
$2700 or less for new.
Another consideration is Don Sachs Kootenay 120 amp.  Another kt88 based amp.  Great piece.
  
try a Carver M500t and forget the Tubes