Thinking about trying a tube amp. Thoughts.

1. Do tube amp owners pursue any active cooling as some SS amp folks do?

Typically no because of the way the tubes work, they need to be hot. They have a heater plate in them and typically that's the biggest draw on power for both the tubes and transformers. So you can blow a fan on them but you run the risk of the glass tubes being cooler on one side than the other and that can cause them to fracture and/or explode. A tube that doesn't hold a vacuum anymore will not work either. So a fractured tube is a dead tube and kind of dangerous to try to run with.

2. Are there be any benefits to keeping the tubes/amp cooler?

For your room, maybe, with less heat but, see the answer to #1 on why it's not advisable.

3. Any negative things in actively cooling a tube amp and/or it's tubes?

See the answer to #1. Just like a car has to reach optimum operating temperature to get the best efficiency, your tube amp has to be hot to do the same. If the tube amp has to perpetually fight your cooling desires, you will never get good performance out of it. You can overheat a tube amp, though, and you can cause the valves to partially open which leads to overdriving the amp and blowing transformers or other parts. So a tube amp shouldn't be crammed into a tight shelf either.

4. Are my SDA SRS (Gen1) speakers something that would work well with a tube amp?

While some had driven SDAs with success, the bigger the SDA the more complex the load and the harder it is to drive. For those who have done it successfully they were using 2Bs or CRS models as they have the least amount of drivers and crossover complexity. When you add the SRS updates to the models, they get even harder to drive. You would need a very expensive tube amp to drive them well enough and the more power your tube amp puts out the hotter it will get. Besides that, SDAs need a common ground amp to be able to run the SDA interface. While you can find common ground tube amps like the old Jolida stuff, the majority of tube amps are not common ground. So if you want to run SDA with them, you will need to make sure that the amp you are looking at is a common ground amp. Otherwise, you would either need a modified SDA interface cable like the SDA Dreadnought or you would have to omit the interface cable entirely and lose the SDA functionality. SDAs are best driven with solid state amps.

This is a forum member's site who has the SDA Dreadnought which was designed by another forum member:

https://www.vr3mods.net/product-page/sda-dreadnought-for-non-common-ground-amplifiers?srsltid=AfmBOoqWz3nxyvbAnBc_BsHGZW6Fs5lCaa3LgPc-RoeA9-CXioIz9wA_

Also, I'm thinking about a nice tube amp would work really well with my Infinity Prelude MTS speakers.
They have a sub that's driven by a B.A.S.H. 850w class d amp.

These are the specs for the Prelude MTS Tower....
Drive-units (all ceramic-aluminum matrix): 1" dome tweeter, 3*"-cone midrange, four 5*"-cone midbass. Crossovers: 300Hz, 2kHz, 24dB/octave. Frequency response: 80Hz-22kHz, ±3dB; 100Hz-20kHz, ±1.5dB. Nominal impedance: 4 ohms, ±1dB. Sensitivity: 90dB/2.83V/1m. Power requirements: 25-500W.

I've never heard to the Prelude MTS speakers but at a 90dB sensitivity and minimum power requirement of 25W, you should be able to drive them effectively with a tube amp in the 20-30wpc range. However, make sure that you find yourself a tube amp that is rated for 4 ohms. Many are rated for 8 or 6 ohms and a 4 ohm load on an amp not rated for 4 ohms will drastically reduce the life of your tube amp.

5. Any thoughts on a tube amp for my Prelude MTS's?

20-30 wpc amp with a 4 ohm load rating. Could give you many examples but without a budgetary number, it's hard to narrow down. Unless you are willing to get a kit and build it yourself, though, a 20-30 wpc tube amp that is 4 ohm stable is going to be a few hundred bucks (300+) for a cheap one from China that isn't absolute garbage. You want a known brand name expect to be closer to a grand for the lower end of the market.

It'd be cheaper to stay with a solid state amp and get a tube-based pre-amp to experiment with the sound and see if you like it or not.

At the same time, though, I think lots of people over-state how much heat a tube amp kicks off. I have had high power solid state amps that will get hotter than a moderately sized tube amp (30-75 wpc). Like Brock said, new tubes are not quite as good as New Old Stock (NOS) from the heyday of tubes. At the same time, though, while it's possible to get a bad tube right out of the box, unless you are giving your amp the beans regularly, a decent tube should last a good long time. They can be a fun experiment or they can also be an audio black...I mean rabbit hole and cost boat loads of money chasing that "thing".

So don't take the info to an extreme. Yes, heat is a consideration, yes, tubes go bad and can be expensive to replace and yes you do need to pay attention to specs, these are not show stoppers nor should they dissuade you.

I've seen many people drop $300+ on a single power cord for an amp and then scoff at $50-$100 for a decent KT88. Yeah, the number of tubes makes it daunting but unless they are cheap like 11BM8's that are $10 a pop 'cause they are used in guitar amps everywhere, getting tubes from a trusted source that will test and match a selected set of tubes before shipping for you is worth the extra cost you might see over a place that just sends out a saran wrapped pack of whatever you ordered.

That said as well, if you are reasonably good at soldering, there are a number of kits out there that you can easily assemble yourself to play with. They aren't going to be power houses but they will be enough to experiment with and finding a decent set of used, vintage JBL or Klipsch bookies is not hard nor expensive, especially if you don't care about how they look. Hell, I've run my set of Polk R15's off a TINY tube amp. You have many options to jump into the tube waters. Then you can figure out if tubes are for you or not and you're not out much plus you learned some stuff. Maybe even make it a project with your kid.

skipshot12 wrote: »

I have a some questions for the pros regarding tube amps.


1. Do tube amp owners pursue any active cooling as some SS amp folks do?
2. Are there be any benefits to keeping the tubes/amp cooler?
3. Any negative things in actively cooling a tube amp and/or it's tubes?

4. Are my SDA SRS (Gen1) speakers something that would work well with a tube amp?
We listen loud with the SDA's being driven by a 500w per SS amp.


Also, I'm thinking about a nice tube amp would work really well with my Infinity Prelude MTS speakers.
They have a sub that's driven by a B.A.S.H. 850w class d amp.

These are the specs for the Prelude MTS Tower....
Drive-units (all ceramic-aluminum matrix): 1" dome tweeter, 3*"-cone midrange, four 5*"-cone midbass. Crossovers: 300Hz, 2kHz, 24dB/octave. Frequency response: 80Hz-22kHz, ±3dB; 100Hz-20kHz, ±1.5dB. Nominal impedance: 4 ohms, ±1dB. Sensitivity: 90dB/2.83V/1m. Power requirements: 25-500W.

5. Any thoughts on a tube amp for my Prelude MTS's?

These speakers can be driven completely, including the subwoofer, with the amp of choice or, it has the ability to allow the subwoofer to be driven by the internal class d amp allowing the chosen amp to just drive the tower drivers.

The Prelude MTS's ceramic-aluminum tower drivers can be a little bright, I'm thinking a nice stereo tube amp may be a good choice for the towers, letting the internal Class D amp drive the subs.


Apologies pearsall, not trying to hijack your thread.

"Active cooling" shouldn't be necessary unless you are using your gear in an enclosed space. A single ended Class A amp sounds better "at temp" than it does super cooled. It's designed to run that way with the transistors in the "optimal" operating area which draws full current. Same for tubes their operating parameters occur at a certain temp. Cooling probably won't harm anything, but most likely will limit performance.

There are plenty of other designs out there that run cool. IMO, they don't sound as good, but if heat mitigation is a top priority then that's how it is.

If you are cooling to prevent "over" heating then I could see. Like I said most class A amps go into great detail about how to place them so they don't over heat.

H9

pearsall001 wrote: »

Definitely gonna pass on a tube amp for my combo HT / 2 channel system.
Will revisit Class D amps. I had a pair of mono blocks a good 10 yrs ago & I really liked them. The technology has advanced leaps & bounds since then so worth a revisit.

Arcam class G will get you the sound you are looking for. Heavily biased into class A to start with...
The do run hot however.

Class G uses a dual rail topology. It's been around since at least the mid 1970s.

It is pretty simple and comparatively low-tech. Not really any more efficient than Class AB, other than the ability to transiently double output power by switching to the higher DC rail voltage(s).
EDIT: OK, Audio magazine said it's quite efficient!

Finally, there is a Class G amplifier
from Hitachi which is designed to op-
erate more efficiently over more of
the operating range. It boasts an effi-
ciency of 90 per cent or better. In-
stead of using two transistors, as is the
case with Class B and D amplifiers, the
Class G uses four. The smaller pair has
relatively low power dissipation and
output, but whenever a higher ampli-
tude signal comes along, a sensing
diode switches on the larger pair of
transistors. Consequently, each pair of
transistors operates in close to its most
efficient operating area, and the over-
all circuit can be smaller and lighter.

source: https://www.worldradiohistory.com/Archive-All-Audio/Archive-Audio/70s/Audio-1977-09.pdf#search="class g"

mhardy6647 wrote: »

Class G uses a dual rail topology. It's been around since at least the mid 1970s.

We had a dual rail Hitachi back in the 70s.

pearsall001 wrote: »

heiney9 wrote: »

pearsall001 wrote: »

The Arcam PA240 looks interesting especially when it claims that the first 50watts are class A.
I've looked at many Pass Labs items over the years but their pricing was always a stumpling block for me.

No way its 50 watts of class A. Not enough heat sinking. They are playing tricks in the marketing department.

My XA25 is 25 watts Class A and even with it's ample heat sinks it gets pretty hot to the touch.

For a few hundred more you could buy a used XA25.

H9

I wonder if being class G has something to do with it. Apparently they rival class D in how cool they run & heat sinks aren't a major concern. I'm with you though 50 class G watts does seem like a lot.

I think we're so used to class A / AB amps with massive heavy heat sinks being a major part of their design that we can't wrap our heads around these new designs that don't require the same cooling needs.

I have not heard the Arcam, but the trick topologies of the past are usually just that "tricks". It's all about trade-offs. Not saying it doesn't sound good.

I have always stated that after I heard my first single ended class A amp, that was it for me. No other amp will do for me personally in my main rig. I am willing to put up with the heat and extra electricity bill.

This has only again been reinforced by the little Pass ACA amp. So simple, such great sound from a low powered single ended class A amplifier. I've been comparing to my Keces E40 and Schiit Gjallahorn amps in the office rig. the ACA wins.

Sorry for taking it a bit off topic. We all like what we like for various reasons. There is no "right" answer really. Maybe more right or less right....lol

All I was saying is if you want some tube character in your amplification w/o actually running tubes; Pass gear and single ended class A in general has the some of those characteristics.

I wish you were closer Phil. I'd loan you my Pass Aleph 30 just so you could get a feel for it. I still have it. Not sure I want to risk shipping there and back for a demo. Not so much for a sale, but just to get your ears on it.

H9

Phil, I will leave you this quote from a Positive Feedback review. Should alleviate any concerns about being up for the task of HT.

In routine listening sessions the Pass Labs sounded a lot more powerful than those numbers imply.

For example, the XA25 easily provided the full spectrum of extreme dynamic performance, whether it was on the subtle gradations of pianississimo, or the "hang onto your hat" blasts of fortississimo, even at live-like sound pressure levels (SPLs).

To accomplish that kind of a live-like level of dynamics at live music volume levels, without strain, normally requires sensitive loudspeakers combined with relatively powerful amplifiers, or loudspeakers of average sensitivity with astronomically powerful amplification.

As part of the feature review I am writing about the Pass Labs XA25 stereo amplifier for Positive Feedback, I've been asking Nelson a few questions here and there about the XA25.

These questions are partly because I'm interested in what makes it tick from a technology standpoint so I can give you a thorough description of it for the review, but also because its high level of performance simply defies what I would normally consider possible from a 25 watt per channel stereo amplifier (into 8 Ohms).

In a nutshell, the Pass Labs XA25 stereo amplifier is extremely transparent, resolving, and distortion free from the highest highs to the lowest lows, and it sounds incredibly powerful in contradiction to its nominal power rating of 25 watts. The XA25 can also provide incredible bass slam when it's in the music, and yet it possesses all of the organic musicality and visuospatial characteristics that I would normally associate with directly-heated singled-ended triodes (DH-SETs).

I use the XA25 as example because I speak about what I know. As far as integrating into an HT, not sure how that would work or if the cost per use ratio is way too high since you do little 2ch listening these days. In fact if you are 75% HT, why are we even discussing tube amps.....lol

It's fun to discuss audio even if in the end it's not practical for your use these days. I admit, my 2ch vets used maybe 2-3 times a month (Fall and Winter more). I spend most of my time listening to the office rig. Even that is more rare these days.

But, for me, knowing I have it when I want to enjoy it is worth the cost. Even if those moments are fewer.

H9

Watts are overrated.

Tom

3 per channel on the big boy hifi at my house. Thermionic watts they are, too... of course.
Not home theater, though.

Levinson has substantial current in their designs, great amps

Phil is always wanting to try something different. I love it!

You know I'm going to say be sure and check out LampizatOr options. One of the top five changes I've made to my rig. Of course, it all started out by seeing what DACs could do with the Geshelli Labs J2 DAC I got from you!

That PrimaLuna was on my short list. You have some nice ones to think about there!