How hot is hot when moving from class a/b to to a or tubes?

It would be a good move for you to try Class A and/or tube equipment given your Zu. I tried a number of solid state Class A with my soul Superfly when I owned them, but I much preferred tube equipment with high efficiency drivers. And low watt also helps to maintain low noise. Some of my favorites with Zu included:

Oliver Sayes Korneff 45 Clone (4wpc) 

Bottlehead Kaiju (300B, 9wpc) with upgraded caps and tubes

Atma-Sphere S-30 3.3 (10-30wpc depending on number output tubes used)

As with any Class A or tube, allow 30-60 min of warm up to sound their best. This doesn’t mean that the system sounds awful before the amp is warmed up, but most can detect an audible difference that brings along additional transparency/openness and dynamics when the amp reaches full heat. I don’t recommend wasting the energy to turn it on prior and come back 30-60 min later as it is just that - a waste of energy and time.

Yes, these units will incur more heat and run up your electrical bill. They aren’t by any means “green”. But with the size of your space, if your listening position is a good 8-9 feet or more from the amp, you probably won’t feel it too much from your listening position. The open space will likely not run up the temperature of the room. If the room were more like 3-5 meters, that would be a different story. But you will notice a bit of a bump in your electrical bill, probably by a couple of bucks each month, depending on how much the amplifier is on. 

All worth it in my opinion, if it brings the sonic benefits you seek  

FWIW, I live in Texas where it gets pretty hot, after going from a set of B&K M140s then a CJ MF2250A both solid state to tube monos by different companies including VTL & Quicksilver & a Pass Labs XA30.5 the heat issue never was a problem till I hooked up a Jolida 302BRC and there was no way I would run that amp inside a cabinet even with proper ventilation due to the heat exchange. The moral of the story is be diligent because they are not all created equal and some will have that as an issue. Enjoy the music

@tooblue - it doesn’t get Texas hot here, so sounds very hopeful. 

@blisshifi  thanks for that. Yeah I don’t feel I am getting what I can from these Zu’s. I will take a look at some of those. It’s close to 9ft away from the amp, so good shout there. 

@mpoll1 It’s my pleasure, and welcome to the community. 

With your speaker’s efficiency you should take a hard look at Valvet Class A amps. They fly under the radar but get universally outstanding reviews and rarely come up for sale but there’s one available now. I’d highly encourage you to check them out. 

https://www.usaudiomart.com/details/649955814-valvet-e2-12-watt-single-ended-solid-state-amplifier/

I’d also mention the Plinius SA103 that is also Class A but includes a very useful low-bias switch that lets the amp run in a much cooler Class A/B mode for less critical listening or if you want to leave the amp on 24/7 so it’s always warmed up and ready to go when you want to do more critical listening in Class A.  Hope this helps, and best of luck. 

My CODA #16 amp with the first 100 watts in Class A and 150 total is just warm not hot. A great sounding amp and the anchor of my future Livingroom system.

My KRELL Duo XD lineup amps, which I sadly sold, were all Class A and ran cooler than the Coda. For, example the Duo 175XD is 175 watts of Class A. It is Class A done like Westminster Labs, using a biasing approach. I was planning on buying the ultimate KRELL amp, the KSA i400, which is 400 watts Class A and runs just warm (another KRELL XD amp). I still may buy it, but I changed course and decided to buy an expensive DAC and use a second-hand CODA #16.

My RAAL VM-1a is a tube-based headphone amp and it runs as hot as a furnace. It sounds incredible and the best amp for the SR1a and CA1a phones.

Though my favorite amps are my Benchmark AHB2 monos and they are Class AB + H and are the coolest running of all my amps. I just wish they were as powerful as the CODA #16 or KRELL. I am listening to RUSH Moving Pictures using the AHB2’s as I type this and damn what a sound.

If you are going Class, A, check out the KRELL XD lineup before spending money on the traditional Class A amps.

BTW - I just read your speakers sensitivity rating. With that speaker do a 30-day home trial of the Benchmark AHB2 amps. It will be great with your gear and cost ONLY around $3K. My CODA #16 is $16K (new) and it is sitting idle in my office while I listen to the AHB2. I always go back to the AHB2.

I have all Audio Research Reference gear… nearly 40 tubes. 140 watts per channel. I just went over and held my hand around one of the power tubes… it was slightly hot… touching it, it felt very warm… maybe hot… but you would have to work to get it to burn you. The preamp has 7 tubes is slightly warm. On top of unit.

I have a large room, never noticed it warming the room… but when it 100+ degrees out my air conditioner is on. It does nothing to warm the room.

I seriously doubt my listening amounts to more than a couple dollars a month. 
 

‘’The design does determine the heat. Some designers use the tubes to their max and will generate more heat and shorter tube life. My tube life is over 3,000 hours per set.

To me this is completely a non-issue compared with the incredible sound quality you get with a great tube amp.

@mpoll1 

Another thought might be to get a tube preamp and a SS class A amplifier or two.  The tubes in the preamp can last 10,000+ hours and throw off a lot less heat.  You can get the tube sound without the fuss and expense of output tubes. Also many companies are making hybrid amps that have driver tubes, solid state output.  I have a couple of amps that are exactly opposite of that.  They have solid state drivers and tubes for the output.

All the best.

Its all relative. For sure SS Class A runs hotter than A/B. Digital amps run cooler. Tube amps run usually hotter than all three, except perhaps for ghdprentice, but, for example I run a 40wt tube amp 10 to 12 hours a day. Puts out a bit of heat but really doesn't warm my house much as far as I can tell, nor does my A/C bill run high. The up side is in the winter I keep my house at 68 degrees and if my hands get chilly I just walk over and put them on the transformers, not the tubes!).  My expense is I go thru a quad of tubes every year and that can be a bit pricy, but it was worse when I ran a big tubed amp and it was two quads. The enjoyment I get from music greatly exceeds the small additional costs involved in running the equipment.  

Also, on warm up. It depends. I could talk about the warm up on the previous versions of Audio Research preamps, in great length. But I really don’t notice much of any with the current Reference models. While earlier warm ups were only 10 to 15 minutes. I’m just not hearing any with contemporary amps and preamps. It used to really stick out… you could not help hear it… but today I am just not hearing it. There may be a little… but if so, really subtle.

I live in a suburb of Memphis TN, gets very hot here during the summer. I have 2 tube integrated amps in my main system which is in a 25x19 foot room so smaller than yours mpoll1. One of the integrated amps is 845 tube based; the other 7189A/EL84M .  It doesn't matter what the season , neither, and most specifically the 845, never leave me feeling that they are heating up the room; nor that the AC runs more in the summer because one or the other are on. Likewise,  I have a KT88 integrated amp in my upstairs family room with similar footprint and that also doesn't heat up the room. Net net, your room is bigger than either of mine and I wouldn't think twice about the "heat issue" in your case.  Cost wise I haven't ever attempted to size up the utility cost factor whether using tubes, or class A/B amps; I'm more interested in musical enjoyment.  I will agree that the tube amps sound better after 30 minutes or so, and I begin listening after allowing the tubes to initially warm up for 10 minutes or so.

I had a pair of Monarchy Audio se-100 Delux class A mono block amps.   They powered a pair of Usher floor standers.   Even at moderate volume the amps barely got warm.   Amazing amps for $900 I bought as factory refurbs/upgraded.    I once brought amps to my friends home to power a pair of Maggie’s.   The amps definitely ran hotter to the touch but not extremely hot.  So in my situation guess it depended on the speaker load

@mpoll1  I have been running two 50 watt tube mono blocks.  See my virtual system to get an idea of the size.  To answer your questions.

Ready to play as soon as I turn them on.  No great warm up period required.  

After they have been running for a while, and at med loud load, the transformers are running at 110 degree Fahrenheit.  My room is 13 x 21.  After two hours of listen time the amps have raised the room temp by 3 - 5 degrees. 

The cost of running tubes vs SS  a few dollars per months.  My SS amps pull 3 amps on average and the tubes pull 6.  I doubt you will notice a difference on the electric bill.  

I had a Pass Labs XA25 amp and it was like 4 60 watt light bulbs on in a small space. You could put your hand on it but if it got any hotter it would burn.

I didn't like having that heat when it was summer. I swithced to SPL S1200 class A/B which runs cool and very happy about that

JH

Exposed tubes can present lethal voltage, extremely high heat (enough to burn) and should not be around small children or pets. Regular maintenance of these devices, if well made, can lead to lifetime ownership. 6336 tube running at 18 watts per side.

Your questions:

warming up time 

additional heat to the home

Running in summer time 

additional cost to run

are trivial. The way I look at it, your first stop is assessing the quality of the power coming in. Are you in a single family dwelling? You wiring from the city line to the meter, or however it is configured, is usually the city's, but they will check it and can pull the meter. You want a clean, well done layout to your service panel and from corrosion at the meter connections to funky wiring, bad grounds, corrosion or some "hot spot" on the panel, you should have it checked. Then look at how you are feeding the system- dedicated lines? That's a sort of minimum in my estimation. 

The cost of tubes is the tubes. Sourcing them is another matter. 

Additional cost to my electrical bill: have no idea. I'm in Texas, it gets to be 110F here in the summer; there are grid warnings, and I usually don't play the system then, just because the grid is less "stable" for lack of a better word. I installed a 10kva Iso Transformer for the system that outputs 4 gauge to a more local service panel, where 4 20 amp dedicated runs of 10 gauge are installed. It is normally a very quiet system. 

Warm up time- 45 minutes for the amps; 3 sides for the cartridge. 

I use to think my two mono tube amps ran hot. Recently completed a custom full Class A 50w solid state amp build with the help of a local tech.  It runs even hotter.

Hot is hot. We pay a small price and inconvenience for the sound - still think its worth it for the type of sound it yields. When it warms up faster, even better! :)

My Pass Labs XA30.8 Class A amp runs cooler than the tubed Rogue ST100 that I had before it.

I can hold my hand on the heatsink and it’s not terrible. It’s also not too bad in the summer.

As to the warm up time, both the tubed Rogue and the SS Pass need about an hour but the change is not drastic. 

Where to even begin…. All of your responses have been really helpful. Massively appreciate the time taken and passion for the subject. 
 

I have take all your suggestions and will start my research for my new purchase. 
 

Thanks again. 

Not hot at all for the amp you need to drive those speakers.

I have 5 tube amps. The smallest ones, 2 wpc EL84, is about 60 watts. My 300b is 150watts, my push pull KT66 is 180 watts. none of those heat up the room. these are measured numbers which are always much lower than nameplate numbers. Most people don’t understand this.

My push pull 6c33c is 400 watts. It does heat up the room.

You need 2 watts. make sure you choose a DHT SET or at least audition one.

Jerry

I have the L-509x and Luxman USA confirmed that the L-509x operates as Class A up to 6 watts, then transitions to A/B.

With high efficiency speakers and modest listening levels, the L-509x likely operates solely in Class A.

My Pass XA25 gets warm. I could not say it gets hot. Even when left on several days.  Pure class A 25wpc. More than enough power for the Zu speaker.

I would be wanting to try a tube SET amplifier if I owned those speakers.

Wonderfully efficient speakers with the Zu.  I have efficient speakers that I run and have been running a Decware SE34I.  The 6 watts/channel is more than adequate.  This runs a pentode tube, the EL34, as a single ended triode.  You will notice a few things about Decware right away.  First and foremost, you can talk to their creator Steve Deckart about any concerns and what you are trying to accomplish.  They are hardly ever available on the secondary market.  I believe people buy and keep.  That is certainly my plan.  Another nasty aspect is you are going to be waiting about a year, if you order.  As to heat, there is some but not a furnace.  As to longevity tube amps and their assembly are almost always fixable.  I have a Dynaco ST-70 that is from the early 60's.  The Dynaco does run warmer than the Decware and the Dynaco has a cage cover.  I have had the Dynaco recapped once and new tubes probably 4-5 times.  I do have to bias the Dynaco occasionally but the Decware is self biasing.  I also have a Audio Research amp that requires biasing.  Self biasing is nice.  You can also get into the fun habit of tube rolling.  It does take some time to warm up.  It sounds good, and is ready to go about 2 minutes after fire up but gets to sounding better after a 1/2 hour or so.  That said, I have an old Threshold Cas2 amp, solid state, that takes an hour or more to find true sweetness. 

@hoosierinohio ive been looking at the decwear stuff. Looks really nice and reviews well. 
thanks

@erikt - I have never thought of the cross over point from a-b. I wasn’t sure how class a/b worked. I thought it was it’s own class. Given what you said there will be no way I am leaving class a. 60-80db as top listening volume. 
I got some -28db attention cables, that really helped get the dial round and really improved the sound and detail. I do however run the loudness on most of the time to give it a little, but needed kick in low end. 

My last pure class A speaker amplifier was a 1987 Classe Audio DR3 VHC. It was designed by David Reich (hence the DR prefix). The VHC stood for very high current.

The amplifier was a work of art that weighed in at just over 100 pounds. It cost close to $5000 in 1987 dollars and ran extremely hot. You could fry an egg on its dual transformer case. It also sounded great. However, forget about using it during the summertime though, as the heat put out by the DR3 VHC could drive you out of your listening room. I also have a pure class A Schiit Asgard 2 that I use to drive my planar magnetic headphones. While it’s built to a much less expensive standard, it also runs quite hot. It tends to be a finicky amplifier yet, with my inexpensive planars (Fostex T60RP and Hifiman H4XX) it sounds quite good. I do believe that pure class A (as opposed to sliding Class A) does sound better than class AB amplification. Just be aware of the heat put out by these amplifiers as well as their inefficiency. 😀

A true Class A amp will always run hottest with no signal. When playing music the current/voltage goes to the speaker and is dissipated there. The true Class A amp then runs increasingly cooler! A little-known fact that most audiophiles are unaware of! My Bedini 25/25 fulfilled this design aspect as a true Class A amp. In use it always started out extremely hot and ran progressively cooler as output level was increased. Stopping playing music it again got hotter until it reached its bias limit.

There are very few true Class A transistor amps. Most so-called Class A amps switch over to Class B after a few watts. A true Class A amp of considerable power will always run extremely hot under zero load and then progressively cooler as output level increases!

All amplifiers can reach their normal operating temperature, but class A amps in general may become warmer internally as if you are driving speakers for up to an hour. If speaker impedance dips, the amplifier will be tasked at supporting them with more current. 

Just make sure you use a Class A amplifier in a dry environment and leave vents unobstructed; so heat loss can occur normally. Otherwise, nothing to worry about...

Regardless of what tube amp you get, I highly recommend if you have kids and/ or pets to get one that has some type of cage around all the tubes! Better safe than sorry for a bad burn or blown amp. 
 

I have a Rogers High Fidelity RHF 200 Mark II w/ two KT - 150 power tubes per side that generate 100+ watts / channel in full class A. Great amp & love it but it gets real hit. I bought the very well made vented lexan cover because I have two very curious cats who gravitate towards warm things. You can still see the beautiful amp & it’s outstanding workmanship but it’s safe! 

Define your description of what is "hot" to you?.  

I'm re-evaluating this myself again recently. May be helpful to compare w/others.

SS: My full-on Class A 50w solid state amp is said to be operating normally when you can hold your hand on the side heat sinks for about a max of "ten seconds", reasonably. Confirmed by the original designer and recent tech who performed checks and upgrades.  Special grease was added to the OPTs for maximum heat transfer to heat sinks, @47-50c temp max, and recently biased up and upgraded.

TUBE: my two mono block tube amps run two KT150 or two KT120 output tubes per amp. Can hold a hand on the transformers for ~30-45 seconds no issue. Toasty warm but not what others might consider "hot". Will recheck actual temp with infrared laser next wk after re-biasing tubes to their max to see what max heat is. I'd expect higher power 211, 845 triode amps to run a bit hotter in full Class-A.  

@decooney 

i kept the hot question vague for the reason you describe - want to get a gauge on how others articulate it. My main concerns were: potential burns to the kids (probably their friends. Thanks @jonwolfpell for the cage comment), how much it will heat my already hot home, anyone speaking about shutdown modes from over heating (there are few Texas folks running them in the summer, the UK won’t be hitting those temperatures), hopefully getting some insight on what experienced owners would do if they were starting out again. 

I’ve never owned tubes so I have too many unknowns. 
My next stage will to start home demos and take it from there. 

A lot of the tube amplifiers mentioned in this thread are much more power than you need.  2 wpc will be enough unless you like concert volumes.  A 2 wpc tube amp will be almost no heat.

Also, my comments above are made without air conditioning.  I live on the california coast and don't have air conditioning.

Jerry

@carlsbad i hear you there. I will be looking at single digit wpc. 
very excited for the next steps. 

@mpoll1 My main concerns were: potential burns to the kids (probably their friends.

Two added points of information have surfaced here. And, if you plan to keep your nice L509x amp and rotate in a tube amp once in a while, going a new/lower power direction will be key for less heat and you can also look at integrated tube amps with an enclosure. Do you want to stare at tubes or keep them enclosed, separates or integrated all-in-one unit?

While some will push for the fleawatt single-ended-triode tube amps down in the 2-3 watt range, there are also some very nice EL84 based tube amps in the 20w range that can be nice too. Thinking if you want something [enclosed], we can also make a plug for this one, makes it nice for those starting out with tubes. Here is another to give ideas. Some used ones out there right now too. Another option, fwiw.

@jasonbourne52 

You are quite right about TRUE Class A. It does run hottest on no/low signals.

Some here have mentioned modern Krells, by which I mean post around 1990.  These do not run particularly hot on no/low signals.  How can this be?  it is because they are not TRUE Class A, whatever Krell may claim.  They run in Class B and have so-called anticipator circuits which sense an increased signal coming in and re-bias the amp to Class A and allow it to morph back to Class B when the volume has died down.

I have never discovered any scientific basis for the claim that this re-biasing can occur so quickly after detecting the increased signal that it can power the sound of that signal.  It seems impossible since the cable runs in the amp are relatively short and the signal is travelling in them at close to the speed of light.  A myth put about by Krell so they could play in Green Park while still claiming to produce Class A amps.  Yes they will exhibit patents but anyone can get a patent.  The issue is: is  the move to Class A completed before the detected incoming signal is amplified?  The patent makes no claim that it is.

No guys.  A TRUE PURE Class A amp like my pair of late 1980s Krell KRS200s, uprated by Krell to 400w per channel runs HOT.  And as Jason says, there aren't many of them.

I can feel the heat from my First Watt class A amp from about a foot away. It runs much hotter than my 300b tube amp. I can tell the difference in room temperature when the FW has been on for a while. 

My Mark Levinson 20.6 class A mono blocks pull 400 watts at idle and run 10x hotter than my Marantz 5 tube mono blocks.  I would swear there is a fan in the amps blowing heat.  I also noticed my electric bill goes up  $100 a month to run the 20.6's.  They are the best SS class A amps that I have ever heard.

Heat definitely varies from person to person and I think room size and location in the world play a huge role in understanding anecdotal information . I have an upstairs south facing room that gets sun for the entire day, I'm located in California, and is only 9x13 and is on the opposite side of the house as my AC thermostat. For me, a class A tube amp and a class A/B BHK250 got my room way too hot to be comfortable during the summer time. I'll be trying out class D next. My font end is all tube and surely didn't help either amp. We will see.