Pass Labs x250.8 vs tube amps

I have a beautiful system. Lumin X1 > BAT Rex 2 pre > Pass Labs x250.8> Sound Labs M545 (ESL) in a tiny room (9x 11 ft).  This system has the most glorious SQ: smooth, detailed and powerful , along with great bass. I would say this sound equals or betters any ultra high end system. HOWEVER, I have a problem. My system takes 6 hours of music playing to sound this good. I had X250.5 and I had the same issue. Leaving it on idle overnight doesn’t solve the problem. It is 15 W class A, so it generates quite a bit of heat, and yet I have to still play music. Because my room is small, I don’t crank up too much- maybe this is the problem, but the temperature doesn’t complete stabilize for 5-6 hours. The top reaches 107 deg in 2 hours, but the front plate doesn’t reach 107 until the 6 th hr when it starts to sound glorious. I have never had a tube amp and I am wondering if I can reach that thermal equilibrium and the glorious SQ faster with a tube amp? I worried about the heat generation with a tube amp in this small room, but X250.8 generates 450 W just idling. This is no worse than tube amps like Audio Research 150 Se, which I demo’d and was impressed by. BTW, I need power in the amp because of the esl speakers.
What do you all think?

Some tube amps , heat might be a issue, with my Defy7, 12 power tubes, heat has not been a problem   in summer months, 
And remember fall temps can make rooms chilly at night, , winters can be frigid, This is when  a  tube amp can be of an advantage.  

I think part of the issue as you have noticed might be because it is a class A amp and they are designed to handle the excess heat and once they reach a certain temperature they really start to open up.  I have a pair of Cary 211 AE amps soon to be FE. They play in class A up to about 75 watts which is more than sufficient to drive my Tekton Design Ulfberhts which  are 98 per cent efficient. The amps sound very good from the start but after about an hour and a half of listening when they get hot , they reach a playback level that is simply wonderful and  similar to what you are experiencing with your Pass Labs amps. 
 I also have a pair of Odyssey Audio Kismet solid state amps and they barely get warm even after several hours of playing but they sound the same from the time they are turned on to when they are turned off. 
 If I have company coming over for a listening session , I will start the Cary amps about an hour earlier to get them at least warm. The downside to this is tube usage but the upside once they get hot is more than worth it.
So in this long winded response is that depending upon the tube amp, you may experience the same issue with them. 
I had a similar issue with my system and it turned out that the pre-amp needed the long warmup. One time try turning on the pre-amp 6 hours before your listening session and see if that makes a difference.
I have a similar issue with my pass int 60. Sounds ok at startup, but takes maybe 3 hrs or more of playing time to sound its best. I just put up with it.
I think expecting 1 1/2 hr for warm up is something I can live with.But not 6 hr.
I could not enjoy music in a small hot room.

I suggest it’s time for you to find some high efficiency speakers that you can then successfully use with a ’not too hot’ tube amp.


what efficient speakers have you found and like/love that you can recommend OP try?
open a window...use a fan.....    You seem to like your sound: don't mess with it.
I think he’s also referring to how much time it takes to warm up the Pass amp before he’s ready to enjoy it. It’s a regular topic. Not unique to Pass amps. My former dual mono class A/AB SS amp was the same way at 6-8 hours, it transformed into a gem once the transformers were good and saturated with heat at 6-8hrs. Parasound has made some progress with 1w standby pre-warming, and even then I demo’d one and still had to run it for a while before it sounded right to me. My mono tube amps I run now take a lot less time to be ready for listening.

My local dealer sells Sound Lab and tube amps only. I’ve heard various SL model speakers there over the past 20+ years. In every case they were running two mono tube amps with the SL speakers. At 86db and 8ohms for your 545s, you’d likely need a (pair) of tube amps if you do decide to go to tube. More output tubes = more heat there too. Last time I was there, he was running a set like the larger 845s (huge) powered by two Quicksilver Mono 120 tube amps with dual KT150s in each, only 100wpc. One mono amp per speaker. While it sounded very nice, seems like many with your speakers run above 250wpc solid state amps regularly. If I had 545s and could not keep the 250.8, tube amps would be my choice. They do sound quite amazing with good tube amps. Maybe not as dynamic as your 250.8 Pass amp, unless you bought some with lots of tubes and back to heat again, IMO.

While you only need one amp now to power your 545s with the Pass 250.8, you’d likely want/need a very large stereo tube amps or monos, and either case, still generating some heat but maybe less time for warmup.

The advantage I’ve found with my QS Mono 120s with two KT150 output tubes per amp, they have fewer tubes, don’t run hot, and never take more than 1hr to fully heat up, even at 45 min they start to sound pretty good.

Having heard a few different tube amps with your speakers, you’d need to choose wisely with tubes before you could effectively displace a Pass 250.8 amp I’d bet. Would mono tube amps be enough power and dynamics for you without buying some heat-monster tube amps, hard to say. Your speakers call for 50-600w. It really also depends on your room. At lower listening levels, sure might get away with 100w tube amps. Or, fans for the 250.8 and call it a day. Good luck.

Roger West, the owner of Sound Labs, thought Atmosphere MA1 (140W) was powerful enough for room 9x11. Because of lack of space, I was thinking about AudioResearch 150SE stereo. I think heat generation will be similar to X250.8 but will it reach thermoequilibrium by 1-2 hr?
Take a look at the Linear Tube Audio OTL designs.  BTW, all their amps can be bridged if you need/want to.
The dynamism of X250.8 is unparalleled. With drums in Angela Brown's band, the SMACK is incredible. As I get older, I feel like I wouldn't mind with a bit less SMACK.

I think I need at least 150W for my 86db speakers, even in my tiny room. Linear Tube only goes up to 40W? (ZOTL40?).
As @decooney indicated, the heat is not my biggest issue. It is the time to warm up. My logic is that tube amps will reach the optimum temperature more quickly than Pass Labs or other SS. Tell me if I am wrong.
If you want more dynamics better bass detail and impact and better highs stay with Pass 250.8.If you like lush midrange get tubes.It also depends on the speaker and the system as well.Tubes will definatly run hotter than Pass 250.8.Good luck.
I own the Lumin X1, fantastic unit!
I also owned a Pass Labs X350.5 and also demoed the X350.8.
In the end, I preferred the Carver M350 tube Mono Blocks. To me, it is much more musical, open and with greater dynamics. Hard to believe a tube amp can be this dynamic.

I also eliminated the preamp and started running my Lumin X1 direct to the Carver Amps. Best of all possible worlds.

BTW, I don’t think the Carvers put out as much heat as the Pass Labs did. And they seem ready to go soon after turn on.


I tried going direct from Lumin X1 to X250.8 and it never sounded as good as inserting BAT rex2 preamp between them. May be it is the tube goodness. If M350 really works for me, I can save a bundle of $. Can you tell me how you like M350? How about reliability, service from Carver?
8 pm til next morning is more than enough warm up.
     Is there another issue. Just on idle should be fine for warm up.

 Mine go on about 8-9 pm, stay idle til 6 am or til I start listening.
   Sure it may take 15 min maybe to sound better, but that’s subjective.

Carver claims that his design makes the tubes run cooler and the tubes should last longer. I think his claim is something like 20 years. But, that is hard to believe.
Bob Carver has always been easy to contact, heck he even flew to my house when I was demoing his speakers. (I didn't like the speakers by the way).
The Lumin X1 with the new Leedh volume control direct to the amps is definatly the way to go.

And, by the way. Since you could sell your preamp, then get Critical Mass 1.0 footers for under the Lumin X1. I also have them under my Carver amps and Niagara 7000 power conditioner.
You will be amazed what they do for the image, frequency extensions, soundstage, etc.


As @decooney indicated, the heat is not my biggest issue. It is the time to warm up. My logic is that tube amps will reach the optimum temperature more quickly than Pass Labs or other SS. Tell me if I am wrong.

You are correct when referring to some of the higher end amps with massive transformers. Most of my tube amps   only take less than 1hr.  I was a 35-year solid state amp guy, back to mono tube amps now days. Today, 45 minutes of warmup, ready to go. I simply don’t have the extra time or patience to fire up my former solid state amps and let them run for 6 hours of pre-warming for a 1-2 hour listening session. Was not worth it, IMO.  

Some of the more modern output tube amp designs and tubes do not get overly hot. I can hold my hand directly on the transformers of my current Quicksilver Mono 120 tube amps for ten minutes straight. Warm, but never hot. The output tubes are warm but not scorching like my older tube amps were at times. Similar to Carver’s amp designs. Ask the designer-mfg-seller to put a laser heat gun on it and tell you what the transformer/tube temps are after 6hrs. Try the same with the Pass 250.8 at 1hr, 2hr, 6hrs and see what you get and when it sounds good to your ears.  If you go with tube amps, hang on to your Pass 250.8 if you can, its a lot of fun to rotate. 
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I own an X250.8. I have had tube amps in the past- CJ and Rouge 

2 comments- my amp is fully warmed up in 1 hour. Next- having had tube amps for about a dozen years, with the X250.8, I do not miss the tubes at all 
Since you have the BAT Rex pre, maybe you should consider a BAT power amp like the VK 255se. Yes it's class AB but it has plenty of power for your panels. I have Apogee ribbons running on a BAT VK 42se pre and the BAT VK 250 amp. Great balanced combo.
@ chungjh 

the main switch on the back is always left on; the switch on the front is turned off after a listening session 
@OP. My listening room is 13x12x8.  I have a PS Audio BHK250, which is a hybrid class A amp with a tube input stage and SS output stage.  My speakers are 89db Tannoy DC8Ti speakers.  It pushes them with ease.  I confident it will push your speakers with ease as well.  

When turned off with the remote, the BHK250 goes into standby mode where the SS circuits stay charged.  I give the tubes about 45 minutes to warm up before doing any critical listening.  It is a great amp.

+1 on the LTA ZTOL40.  I auditioned it for about a week.  It is a wonderful sounding amp.  I believe it will also push your speakers with ease. It tubes last between 5000 and 10000 hours.

I settled on the BHK250 because it sounded better with my PS Audio BHK preamp and DSD DAC.

Both PS Audio and LTA have 30 auditions and no questions asked return policies.  You might want to give them a try.
I own a Ref150 SE, it is at its best in 35-40 minutes but I must run an AC unit 12 months a year to be able to stay in the room ! LG 12MBH mini-split with low ambient kit for winter months, use it with Magico V3 ( not the easiest speaker to drive) never used it with ESL though... excellent sounding amp IMO
Why don't you try getting a heat lamp and aiming it at the the heatsinks for 30min before play? That's a $20-$50 experiment that is a lot cheaper than getting a new tube amp.
I have the Metronome Technologie C6 (tube) and the Wavac 805m :they does not give the heat you think. In a half hour he sounds great. After one hour:it’s optimale !
hi, i had great expiriance with  vitus ss-025, it has 25 watts class a , 300 class  ab into 8 ohm and 600 into 4 ohm... after 2 hr. +/-     it sounds like magic- fantastic.  the closest i ever heard ss amp to tube sound...  and when not listning i leave it on mute...
6 hours is surprising to me. I’ve spoken to Kent at Pass. The Mosfets perform to their specs when they reach 50 degrees Celsius. That’s about 125 F. If you leave the switch on on the back I think the unit warms up in a little over an hour. But now you’ve made me curious. I’ll leave it on for 6 to see for myself. Btw, after 3 hours, I can put my hand on the amp and it feels like a warm, not hot cup of tea.
No offense...this is when I believe being a mere mortal financially works to my benefit.
I tried to speed up the warm up process by putting a towel over the amp. This is what Kent English at Pass does before shows. It does get the temperature up much quicker. However, it still took another 2 hr of music playing to sound GREAT. Kent thinks it is the diff pair in the input stage which runs at a constant current and it can't be fooled.
Your Vitus runs class A up to 25W. Doesn't it generate a lot of heat if you leave it on all the time on idle?
Similar topics surface periodically about the 250.8 over on AC.  This thread is from a few years back, 1,2,3 pages worth...warmup, standby / master switch, SS vs. tubes.

Your Vitus runs class A up to 25W. Doesn't it generate a lot of heat if you leave it on all the time on idle?
I own a BAT VK-33SE preamp and VK-255SE power amp.  My speakers are 88 Db efficiency.  The amp drives them effortlessly, with plenty of safe headroom, and I find it to sound it's best after about 30 to 45 minutes.  It gets quite warm by 30 minutes, maybe you could say hot, but never a room heater.  BAT products work very well with one another.  They are designed and engineered to do so.  The VK-255SE amp is one of the most "tube-like" sounding solid state amps available.  Since you have a BAT Rex-2 preamp it would be a very good decision to match it with a BAT power amp.  That's one suggestion.  Another suggestion is to get a BAT tube amp.  The Rex-2 power amp (as well as the Rex-2 preamp) have both been recently replaced with the next-generation Rex-3 products.  Thus, the Rex-2 power amp can likely be had at a nice discount.  You may wish to contact Upscale Audio about that.  They have a Rex-2 power amp set up as a demo unit.  It is only switched on when a demonstration is requested.  I visit the store fairly often and can tell you that amp is in absolute perfect condition.  Upscale Audio is a wonderful retailer to do business with.  I am confident they would work a nice price for you on that unit.  Anyway, I thought you may want to take into consideration pairing your preamp with the engineered mate of power amp and also provide you with a very good path for such opportunity.
Best of luck to you. 
I have an LTA reference 40 amp paired with a Don Sachs preamp.  I used to drive a pair of very difficult Maggie 3.7i's with this setup and had no problems.  That amp is a giant killer if there ever was one.  Just stunning.  Keep in mind it's not necessarily watts you are looking for but current.  And those el34 tubes give you plenty.  I would try one as you get a 14 day no questions asked return policy.  You may be greatly surprised.
As an X250.8 owner with a First Sound tube pre amp I find that an hour or so is all that’s needed to achieve 100% optimum playback sound quality.  If the system improves after 6 hours I’m unable to hear a difference. 
I am very surprised that ZOTL 40 is powerful enough to drive Maggies. For Soundlab panel speakers, they recommend >200 W, like Atma-Sphere MA-2.
There seem to be some pretty darn good Class D amps hitting the market. High wpc &  Low cost. Are Sound labs bi-ampable?

Or buy a couple Magtechs from Roger Sanders and solve all
your power needs. 
Sound labs are not bi ampable. Anyone have experience with high end D class amp?I know they are generally poo pooed, but who knows-may be there has been sufficient progress recently. 
My Viva "Solistino" is an 18W class A integrated  amp. I usually  turn it on for 10-15 minutes for warm up, it does sound a little better after 30 mins. And the IA runs very hot.....can't imagine a system that takes 5-6 hours to warm up.
Sound labs are not bi ampable. Anyone have experience with high end D class amp?I know they are generally poo pooed, but who knows-may be there has been sufficient progress recently.

Class D you say?  How about Tube + Class D monos 600w @8ohms.  Effective to drive your Sound Labs, with ease. Quick warmup, and ready for listening.
PS audio Mono 1200s.  Ultra-linear, high-current, ICE Edge Class D technology for the output stage; and a discrete, Class-A vacuum tube for the all-important input stage. 
I think @ebm is right.
I use a X350.8 and I believe your X250.8 is warmer sounding. I don't think it will ever be the same as a tube power amp.
I like a warm and full midrange and don't think any solid state power amp will ever give me that close enough to say a Conrad Johnson. If my speakers didn't need the high current and I could live with the heat and cost of retubing, I would have gone for a Conrad Johnson.