How hot is too hot?

[MDFreaK76]

As a server guy by day and a Vacuum Tube Newcomer, I find myself at odds with this perplexing little contraption I've Frankensteined in my basement. My time in the world of transistors has taught me that heat is the enemy, and manufacturers and engineers go to incredible lengths to minimize this. My amp, on the other hand, was built exactly to spec, and it could easily moonlight as a space heater. So here's my question...

How hot is too hot? When (if at all) do i need to be concerned? Do i need to limit how much i use it, or how long i use it for? or am i being overly cautious? I've always heard tubes got hot, but as a first time owner, i feel like i need someone to pat me on the back and tell me its ok.

Sorry if I'm a bit paranoid, here. I'm just not used to the idea that this much heat is a good thing.

Cheers,

-Rick

[Maxwell_E]

They are nice and cozy, I don't even miss my fireplace. I have no personal experience with the Crack, but my SEX amp will get quite warm after some use. It seems standard that most electronic parts are good for at least 85C, with 100C being very common. The only thing that can go south is film capacitors, and as far as I've read here that is only a risk for Jupiter's line of Beeswax caps. Someone smarter than me will chime in soon.

[Doc B.]

It's a vacuum tube. They need to generate heat to emit electrons. It's OK.

[adamct]

I was happy to see this thread, because I was asking myself a related question last night...

I was listening to my Crack for several hours, and the chassis plate became quite warm. I won't go so far as to say hot - it wasn't painful to touch - but I was surprised by just how warm it had become. Now, I know that tubes get hot and are supposed to...but what is causing the chassis to get hot? The tubes sit above the chassis, and heat rises, so I would have expected the plate to be relatively cool. Is it the resistors that generate heat? Or something else?

FWIW, my Crack sits 1-2" off the ground, with plenty of room for air to circulate underneath the case, since I had to raise the case to provide clearance for my film caps.

Best regards,
Adam

[Grainger49]

I guess this thread, my thread, is in the wrong place.  It doesn't get read.  Neither do Dan's threads about buying used or basic troubleshooting.

Heat is FAQ #4:

FAQ Thread

[Doc B.]

Power = Volts x Amps. The cathode resistors (or speedball transistor/heatsinks) have roughly 75V at .035A going thru them. That's a bit over 2.5W of heat being generated under the chassis by each channel.  There are also resistors in the power supply generating heat, rectifiers too. The tube pins also conduct heat from the tubes into the chassis.

So don't worry, unless the thing doesn't glow and make heat.

[MDFreaK76]

Thank you all. I honestly DID read your FAQ, Grainger. You warned me that it would be warm, and just like you said, its more than i'm used to.

Its kind of like when i was looking at this amp to begin with and reading all the reviews, and ^{everyone said it was awesome and it changes how you hear music and blah blah blah...}

Truth is, some things need to be experienced to be learned. 

[adamct]

Thanks. FWIW, I wasn't concerned, nor was I troubleshooting (my Crack sounds great!), it was more that I was just curious as to the source of the heat. My knowledge of electrical components is, ummm, errrr, close to zero. I speculated that the resistors were the primary source of the heat, but wasn't sure and in any case I was surprised that such small resistors can generate so much heat. Sounds like the answer is resistors, transistors and rectifiers all generate heat. Thanks!

Best regards,
Adam

[Paul Joppa]

Obviously the tubes themselves get hot ... also the power transformer has resistance in the wires, which generates heat, plus the magnetic laminations have magnetic losses (hysteresis) making heat as well.

If you ever have a biig solid-state amp that runs in class A, you'll notice it generates a lot of heat, too.

[Paul Birkeland]

If you ever have a biig solid-state amp that runs in class A, you'll notice it generates a lot of heat, too.

I had a 25 watt per channel class A solid state amp that was uncomfortable to pick up after it had been running for a while because it got so hot!

[4krow]

Out of some of the same curiosity, I used a laser thermometer on a few parts in a small buffer amp. The only reading that I recall at the moment was the solid state rectifier.at 209 degrees F. Quite a lot more than I would have thought. Seems like the 6SN7 tubes were above 135F, but I could be wrong. No doubt, it is not what we might be used to, but it is what it takes to make sound.

[Grainger49]

I had a Krell KSA-250 S.  It weighed 145 pounds and ran HOT !  That was two steps back from the Paramours.

BTW someone built a custom base for their Bottlehead product using a fan mounted at the rear of the base.  It looked good and running cooler is bound to make the internal components last longer.  Well, there are Bottlehead amps out there that are 15+ years old and the only thing they probably need is updated caps.

[adamct]

15 years from now I plan on building the great-grandson of the Crack, not replacing the caps in my current Crack. 

I'm still looking forward to the potential high-end OTL amp, although it is tough to believe that any improvements that could be made to the Crack from a technical design perspective would actually result in better sound. I'm sure everyone here scoffs at that idea, but I don't say it lightly. I've now compared the Crack to the following amps:

- Woo Audio WA22
- Woo Audio WA6
- HiFiMAN EF-6
- HiFiMAN EF-5
- Lake People Violectric V181
- AMB Beta 22 (fully balanced, 4-board build using top-of-the-line components)
- AMB M^3
- Little Dot Mk VI+
- Audio-Gd ROC SA
- Audio-Gd NFB-10SE
- Earmax (original version)
- Purity Audio K.I.C.A.S. Caliente
- Neco Soundlab BOSFET v2.1 (PCB v7)
- Eddie Current Laconic EC-01

When used with my Sennheiser HD800s, the Crack bests them all. The only one that really comes close is the LD Mk VI+, which is also an OTL amp and can also use 5998s/6080s/etc. Since many of those amps cost many times what a Crack costs, I can't help but wonder whether a more complicated design, even if technically superior from an engineering perspective, would really result in audible improvements in the sound. The only area where I can imagine room for improvement in the Crack would be in lowering the noise floor, but to be honest with you, it is already very, very, very low, certainly below the point where it has any relevance whatsover, including during quiet music passages.

Still.....there is only one way to find out!  It could be the case that my lack of imagination on how to improve the Crack is due to the fact that I am constrained by what I have already heard and know. And having an excuse to build another Bottlehead kit doesn't strike me as a bad thing... 

Best regards,
Adam

[Paul Birkeland]

Well Adam, you really hit the nail on the head in terms of what Crack developments look like.  We have built quite a number of experimental Cracks, and it has been difficult to get significant performance improvements beyond a stock Crack with Speedball.

For a high end OTL amp, we would certainly try to shunt regulate the entire circuit, include additional inputs, and use my attenuator design.  Since the Crack is philosophically similar to a Foreplay preamp, all the decades of research and development that went into improving that kit gives us some good hints about what we can do to make additional improvements beyond what we have now.

For now, I'm stoked about the level of performance achieved in the Crack for its price point, and I will continue to work hard to maintain that balance.

[adamct]

Thanks, Paul. The only thing I would add is that the Crack (and Crack + Speedball) offer a price/performance ratio that is almost unmatched in my experience. While I wouldn't want to pay more for no gain, I don't have a problem with paying more -- even significantly more -- for some appreciable gain. In other words, don't be too hesitant to stray from the value model of the Crack. As long as the Crack is still available, Bottlehead's reputation for value won't be jeopardized by introducing a premium model that offers less value for money. Choice is good!

And I hope that your experience with the Smack won't dampen your appetite for experimentation in this area. To be honest, I can see why people had trouble differentiating between the Smack and the S.E.X. They were both WOT, they were too close in price and ultimately they both had switchable output impedance. With the S.E.X. having greater power, and given that the introduction of the Smack coincided with a huge upswing in interest in inefficient planar headphones, it was perhaps inevitable that those faced with a choice would go for the similarly-priced, more powerful model. The other problem, of course, is that most customers don't get a chance to A/B your different models, so they are left grasping for words or specifications that somehow distinguish between the two. Differences in specifications are easy to grab onto. Words describing differences in sounds and refinement are more difficult, especially if the differences (or the words describing those differences) are too subtle.

In any case, I look forward to whatever new model will replace or completement your existing offerings!

Best regards,
Adam