It depends on amp's circuit design more than on type of tube being used. Most of SETs are using primitive amature DIY design, but tubes in SETs last quite a long time before anything serious can happen. There are ways to prevent bad tube to blow:
1. Turn off tube amp when you're not listening to it. It takes only 5m to get tubes to the normal operation.
2. Eyeball the tubes having a normal glow when you play the music. One tube that will glow too bright or too dim might not be normal.
3. If you hear microphony, inspect tubes.
4. Have extra set of tubes. It helps you to check if problem goes away after you swap for the fresh one.
No experience with the 845's, but generally catastrophic failures are pretty rare in tube amps. Yes, the tube may fail but the minimal number of parts in these amps means that there aren't a lot of things to go wrong. Output transformer isolates the speaker from DC so you're pretty safe there. Output transformers do NOT like open circuits when signals are present so make certain that speaker leads are hooked up properly before engaging the source. Enjoy!
Thanks for your responses. I agree that the amp's circuit is very important and that's why I'm considering the deHavilland.
I never leave tube gear on and unattended for very long and always keep plenty of spares around "just in case." I also have a Hickok tester and keep pretty good tabs on my tubes.
I was hoping for a few more responses from those who've lived with the 845 for a while, wondering how reliable they are and what I can expect if one fails.
Again, thanks to the two who responded!
I like the DeHavillands a whole lot, and think they're built pretty well, but some other amplifiers can present real issues when faced with this sort of thing.
Two specific incidents I saw with the Opera Audio/Consonance Cyber 845/211 (same amp that uses a different bias resistor to run either tube) when I handled them came from excessive current draw by the output tube.
The owner of the 211 amp was going through components in the power supply over time. The amp had previously been repaired; when it failed again, it came to us. We discovered the 211 was drawing more current than it should, made the repair, and advised him to buy a new set of 211 output tubes.
The 845, which were a more or less new pair of amplifiers, were the more hairy. Same sort of issue, but the tube was less sound than that just described. It completely barbequed the power transformer. Supposedly, the amount of smoke was incredible. The owner was truly lucky to be able to power things down as quickly as he did. Otherwise, his home might well have burned up as well.
A friends tube power amp went up in flames a few years back. The technician that tried to repair it said the cause was a faulty new tube that the friend had installed a few days earlier.
I've been using hifi tube amps continuously since 1970, as well as guitar tube amps and of course I'm old enough to have had tubes in my life continuously, as I was born into the world of tube radios and TVs and hifi then ensured the persistence of the vacuum tube for me. The most spectacular tube failures in power amps that I've seen were 6550 implosions in the early unstable Audio Research Dual 75s of the mid-70s, and the broadcast power tubes in early Futterman OTL amps of the same period. Even in those cases, needed repairs were limited to the amps themselves.
I've been using Audion Black Shadow 845 monoblocks in one of my systems for the past seven years with no tube failures. I use the Shuguang 845B tube of which my current pair are now coming up on five years old, and still test well. I have had two 845 amp repairs in that time -- one elective and the other necessary. The elective work was a choice to recap the power supplies in the amps, for sonic improvement. In the second case, recently, breakdown of a filament supply bridge rectifier caused a massive rise of hum but otherwise the amps operated. I had the rectifiers replaced inexpensively. In a high current filament supply like that needed for the 845's thoriated tungsten, the rectifiers get hammered. They probably should be routinely replaced every 5-6 years.
845 tubes are typically (but not always) run with B+ of 1000v - 1200v. The filament supplies consume fairly high current compared to heaters in more prosaic tubes. The filament rectifiers in my amps are rated 25w, for example. If there is a filament short, some associated components will fail and in any amp this *can* but generally won't fry the filament winding in the power transformer. Usually the rectifier will fail if it's a DC supply, along with a resistor or two. Or the power supply fuse will blow, protecting the transformer. This is not unique to the 845. If the tube goes runaway or otherwise degrades, again it is possible to see the power transformer fried, but more likely some associated components in the signal path and in the power supply filtering might get taken out before a slo-blo fuse melts.
For amps of the design caliber of DeHavilland, Audion, Sophia, you are highly unlikely to see the smoke, literal glass envelope implosion and occasional flame that were occasional risks during the rebirth of tube amps after the transistor take-over, during the early years of what we now call "high end audio" in the 1970s. My Audion 845 SET monoblocks meet or exceed the reliability of any amps I've owned prior. More often than not, an 845 tube failure is a quiet non-event as the tube just dies either by defect or end-of-life dysfunction. In the latter case it starts sounding poor before that, prompting you to replace it.
Use common sense. When you buy new 845 tubes, look and listen inside, for loose metal parts or solder scraps. Quality control lets some bad tubes slip through, and shipping can shake loose some marginal internal construction. Don't install tubes with loose internal metal!
Thank you for that.
Phil, now that's the kind of useful info I was looking for!!! Thanks for taking the time and being so thorough.
Joe/Trelja, thanks too for your comments. You and I discussed the merits of the 845 a while back and I'm still dragging my feet. I know it's not your favorite choice for SET but the only other amps that peak my interest are the Wavelength Cardinal's. I'm fearful the 300B will fall a bit short on power and probably be a little "soft" compared to the 845. Yah, I know, many feel the 300B has a more interesting sound.
There's nothing about a 300B that gives it an intrinsically "more interesting sound" than an 845. The differences are in execution more than the tube itself, though there are some characteristics that correspond to the power tube chosen. If you doubt this, get a 300B amp and then listen to Chinese solid plate, mesh plate, Sophia, Shuguang or TJ high-metallurgy, KR Audio, EAT, JJ and Russian 300B variants in it, and you'll hear that it's not the 300B that makes a 300B amp "interesting."
But look, they're both triodes, and applied single-ended, they will sound far more similar than either tube will to a push-pull implementation, or to a single-ended tetrode or pentode amp, using KT88 or EL34, respectively.
I have Audion Black Shadow 845 SET monoblocks on one system and Audion Golden Dream 300B PSET monoblocks on another. Sometimes I change which system each pair is in. The two amp types have the same power rating, but the 845 have more drive; the 300B have a little more finesse. But we're talking degrees. The 300B PSET amps have more silver in them (wiring + transformer secondaries). Both are solid state rectified. The input sections are similar; the driver tubes are the most different element.
I have had a number of very good 300B SET (not PSET) amps, and have had numerous 2a3, 45 and 6c33c SE amps come through my systems. The Audion 845, and I'll also say Sophia 845s had finesse and tonal density competitive with other makers' 300B and lower power SET amps. As well, most 300B amps have had too little discipline in the deep bass region to be usable on truly full-range speakers. I'll go further to say that to 70% of everyone who has heard both 300B and 845 amps on my main system, the 845 amps have the "more interesting sound," because of their dynamic energy and overall more vigorous drive.
There are many very fine 300B SET amps, including Audion's own, Coincident and Wavelength, but even on highly-efficient speakers, there is intrinsic value to the power and drive of a well-designed 845, for transient dynamic clarity that doesn't sacrifice agility, transparency, speed and finesse. Yes, equally well-designed 300B and 845 SET amps usually sound somewhat different from one another, but which one is "more interesting," will depend on what you value sonically, on a polar graph of imperfection.
If you have clarity, musical realism, speed and convincing tonal completeness from an 845, as well as same from a 300B SET running only 1/3 - 1/4 the power, the dynamic factors of having the 845's reserve and punch will show differentiating value even if you listen at moderate volumes. And to get the same power and clarity from 300B PSET will generally be more expensive to produce with all other factors in league or better. So don't discount a good 845 alternative on rumours of 300B SET being "more interesting."
My 300B PSET amps are among the 3-5 best power amplifiers I've ever heard at any price. They cost 50% more than my same-power 845 SET amps and they also better any 300B SET amp I've heard. My 845 amps are also in that class of 3-5 best amps so far. My 300B PSET amps couldn't be built and offered to the same retail price.
I like both; I have both. But if I could only have one, I'd have the 845 for being more versatile, more convincing in a wider variety of circumstances because of the 845's more robust dynamic behavior and it's better deep bass discipline. Other factors are fully competitive. In the context of having the 845 already, then the 300B PSET are appreciated for their more intricate finesse, though unmistakably at some comparative loss of drive.
Either tube can reside in a poorly designed and executed circuit that negates all of this.
I'm not sure, but I've heard it from reliable sources that a bad 845 will explode, showering the room with glass and poison gas and killing everyone within a 3 mile radius. But that's a risk I'm willing to take.
Phil, Thanks again for your excellent input. Many of the points you make, I've either heard or read before so I was already thinking along the same lines. All things being fairly equal, the extra power of an 845 seems preferable to the alternatives and certainly provides more flexibility.
Chayro, thanks too for your comments. I'll make sure to wear a protection suit when I'm listening!
213cobra, "most 300B amps have had too little discipline in the deep bass region to be usable on truly full-range speakers."
Although someone here recently disagreed vehemently with me on this point, I agree with Phil's comment.
Also, I might have heard the same 845 amp Phil uses at a Zu get together two months ago here on the East Coast, though I'm not sure.
Bob, I've been around the DeHavilland 845 monos you're considering, both at the local dealer who had it on display, and at the customer (our own Sbank) who wound up purchasing it. They're quite a competent, and I believe, well-engineered pair of amplifiers.
That said, I'm going to guess the amplifier is going to be used in powering your Fried C3/L-C4 satellites. Is that right or wrong? If it is those speakers, as we've discussed many times, you don't need very much at all to drive them, and low end isn't a concern in this instance. After yesterday, where I was at an old tube amplifier builder friend's workshop, and we drove an old pair of Dynaco A25 with a 2 wpc 45 SET amp, I'm more convinced about the Fried's requirements than I was before that. No matter what you go with, the Frieds will be more than fine.
Joe, correct, the 845's will only power my sats, running full range. It's amazing how much cleaner and extended bass is since Joel and I switched to the ScanSpeak's. Bass duties still relegated to powered subs(blended in around 50Hz).
I picked up a couple pairs of the rediculously priced Dueland Cast caps not long ago and am anxious to hear their effects. With only one cap and two inductors in the x-over, everything matters.
Joe, I forgot to mention, "Charlesdad" brought over his 8 wpc 300B Coincident Frankenstein's a while back. He wanted to hear them in my system with my MP-1 and I was glad to oblige.
Running only my sats(they're not really Fried's anymore so Joel and I refer to them as FrankenFried's), in my 28'x 22' great room with 11' ceiling, 8 watts was more than enough to fill the room at SPL's that were more than adequate and then some. Really nice amps!
Personally though, I'd still prefer a bit more power and control, thus my interest in the 845.
Bob, I think you've been considering the DeHavilland 845s for over a year, correct? Pull the trigger on those amps already!
As you heard, the true TL (though most don't know, Bud insisted TL was MOST critical for the mids, not the low end) Fried C sats do not need any more than an SET to drive them. And, for me, driving a loudspeaker means a minimum 95 dB at the listening chair without breaking a sweat.
The wonderful, surprising, and (to most people) impossible to believe thing about the series crossover Bud espoused is that you almost gain the ability to divorce yourself from the choice of amplifier. By that I mean, by varying the ZETA value, yet still keeping them first order in the truest sense of the word, you can make them sound as forward as a pair of Lumenwhites or as rich and luxurious as any Vandersteen. Or, looking at it from the amplifier perspective, as lively as Naim or as relaxed and liquid as a CJ. All of this, for the very miserly sum of a couple of caps and a coil. So, that's always a consideration in lieu of amplifiers if you seek to alter the sound down the road - after the DeHavilland 845s, of course.
PLEASE let us know what you think of the Dueland caps in those beauties when the time comes.
I just happen to come across this thread while browsing today. Bob I thought my Frankenstein MKII driving your speakers was quite exceptional sound in your large room. The combo filled the space and was very dynanmic,transparent with liquidity and just plain good musical pace and flow, nice match!
Bob I think you should purchase the 'lusted after' DeHavilland 845 amps,I`m certain they`d also make a superb match with your speakers.Before Arthur Salvatore got his Frankenstein amps he had stated much high regard for the Dehavilland SET amps.
It would be a lot of fun to compare(friendly of course) these two fine SET amps and note how they differ based on output tube and circuit.
Joe, what you say about varying ZETA is certainly true; Joel's been saying the same thing for a long time. That said, there's no substitute for good amplification, especially with speakers as revealing as the C's.
In my mind, 1st order series is THE way to go. Very few parts in the signal path and no big surprise, when we eliminated the resistor on the tweeter, dynamics and clarity improved tremendously.
Charles, yes, your Franks sounded wonderful and as mentioned previously, mated beautifully with my speakers. Big, open, spacious, organic and just plain easy on the ears. Your Franks are the reason I was considering the 300B in the first place but in the end, I'd still prefer a few more watts; call it extra headroom for those musical peaks.
Both of you, I wouldn't say I've been "lusting" after the deHavilland's but yes, I have been thinking about them for a long time. Problem is, I'm "married with children" and don't want to part with my Atma-Sphere MA-1's; or anything else for that matter.
Finally Charles, it would be fun doing a "friendly" comparison between the Franks and the deHavillands. My guess, they'd both win!
"Married with children", I understand all too well(but is`nt it wonderful). I must say your speakers were very impressive, open, transparent,natural and full of life.
Regarding the Dehavillands I`ll admit I`m very curious to hear them in your fine system vs your Atma-Spheres(two sucessful but different approaches). You have your priorities in order,but if you ever get around to it.....
Rfogel8, "there's no substitute for good amplification, especially with speakers as revealing as the C's."
You know, Bob, you're absolutely right.
As time continues to pass, I find it crushing that technologies Bud Fried evangelized like true TL midrange loading, where the music simply flies out of the speakers in a way that makes so many others sound like they're running in peanut butter, and the incredibly wide degree of tuning ZETA provides continue to disappear into the ether.