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By simple, I mean not loaded with tubes (Transcendent) and not loaded with a high price (Atma-sphere 60). Simple parts, even low-ish power, and *reasonable* price (<1,500 U.S. dollars?). Features and big power and flexibility and tube-rolling - forgetaboutit. Thanks. Oh, low-heat would be a plus. Don't trust hot tubes (!)
I am concerned that you are just trying to stir things up???
Your post over at general seems (inflammatory?) related to these
honest, kind hearted recommendations.
Are you actually shopping for an amp?
Or fishing for information in a sneaky sort-of way.
I am sorry, IF incorrect - this manner looks bad to me . . .
Yes, I did post a related question on the 'General' board of the Asylum. Why suggest I'm trying to hide the fact. Would you like to act as my "New York Times' advertising agent and publicize the fact. Feel free. You're observant, too. Or perceptive.
"I'm sorry IF incorrect" - what kind of after-the-fact, after-the-charge weasel apology is that? (and yes, that question is slanted and worded against you; and, no, it is not meant to stir things up).
To answer your biased-against-me questionING, after posting the question on THIS forum, I got to thinking about used amp purchasing in general and THEN posted on the 'General' board. Do you want to research the timing of each post? Go to it.
Both postings were sincere (though the 2nd one on the 'General' board was a biased one and one with implicit assumptions. Where's the danger? Where's the harm? Where's the deceit?). On this board, I thanked the respondents, I think, two times. Where's the lack of gratefulness? I'm not "shopping for an amp" in the immediate sense. Does it matter? Isn't learning for its own sake valid? Do you want purchase receipts when I buy? Do you consider it within the realm of possibilities that I'm posting for a friend? Are *those* type of questions allowable and permissable? Define my limits.
"Fishing for information in a sneaky sort-of way"
Where's the secrecy? I think you have a real problem? Look for your shade of paranoia in your home (or wherever you call home). I'm sure you'll find all kinds of covert activities: under the bed seems a favorite among UNtrustworthy sorts like yourself.
even to the excessive point of ""quoting"" your very words. What do you want: me to visit you and interview you? You're a basket case.
Since you are in Asia, Singapore as indicated by your user information, you might find some prices higher than in the US. However, I agree with those suggesting used M-60s or M-50s which should be well suited for driving your Magnepan MG1.6QRs if your budget doesn't allow you to purchase new.
The Transcendent sound SE-OTL has a total of ten small tubes. Power is low and it runs warm but does not heat up the room. Also you can build it as a kit for $795
Actually, the Atma-Sphere amps are the picture of simplicity. Single gain stage, one set of coupling caps, integrated bias supply, zero or low negative feedback, two tube types.
If you're looking to spend around $1500 you should be able to find an older set of Atma-Sphere M-60s (or even M-50s) in this price range. In the older models, try hard to find one that is handwired. It's ok if they have the small circuit board for the power supply. The handwired units are much easier to upgrade than the circuit board versions.
And with respect to hot tubes, you're never really going to get away from that in any Class-A amplifier, tube or SS. There's no way around the physics involved.
price-wise. Buying a used tube amplifier makes about as much sense as using used toilet paper. Sans smells (!). Again, thank you for your response. I'll look into what you say. Maybe I should not be looking at Class A, then?
and lovely VAC pa80/80 for sale in the Asylum's classifieds. Very tempting. There may go my prejudices!
Nope. OTLs can operate in Class A, AB, or B, just like any transformer-coupled tube amplifier. Some do operate in Class A up to a certain power output and then flop over into AB mode or some variant thereof. Futterman-type amplifiers (e.g., Transcendent, NYAL, etc) operate in AB or B mode mostly.
Circlotron type OTL's operate in Class AB as well. Mostly B.
Using a circlotron with 8 6as7g's with 550ma. idle current each bank. When one bank rises to 1.1amp the other bank will be at or approching zero. That would give you 1.1amps across 8 ohms. That's about 5watts rms. From there on up, it's Class B.
Paul Speltz wrote a very interesting white paper on the operation of the circlotron that was available on the defunct ASOG website. According to his argument (based on actual experimental measurements), the Atma-sphere circlotron can go more into Class A than one would calculate by the standard method you have applied above. I am struggling to reconstruct his findings in my head, but I can't recall the gist of it at this moment. If the ASOG Tweaks section is available anywhere, you might be interested. Paul is a very smart, thoughtful guy and has no ax to grind one way or the other. But you are correct in general that the circlotron will eventually end up in Class B at the top of the power curve.
I thought we had this discussion. FWIW Fisher made an amplifier back in the 50s that was class A2, like our stuff is. We can drive our tubes into cutoff, but at that amplitude the amplfier is clipping.
As for me, if your post was meant to speak to my statement about the circlotron ending in Class AB or B operation at peak power, I am not qualified to argue, nor would I wish to. I will have to go back to my books to find out the differences between AB and A2 classes of operation. (I think in Class A2 the grids of the output tubes are driven positive.) I am thoroughly convinced that the Circlotron has most advantages vs the Futterman-type output stage in OTL designs, regardless of the semantics.
It's a matter of whether or not the current is moving equally up and down. Output tube bank #1 vs. output tube bank #2.
If the current goes up in one bank 600ma. from the starting point of 550ma., which it must for the amplifier to make________(you tell me) watts, the other bank can not go down 600ma. if it started at only 550ma.
In a true Class A amplifier the output stage current draw from the power supply does not change from no signal to full power. (Oh, it changes a little due to non-linearities in the tube, but only for that reason. Not because one bank has stopped going down because it has no where to go.)
If one output tube bank cannot reduce it's current at the same rate as the other output tube bank is increasing it's current, then the current draw on the supply will go up. And this is no longer the type of Class A as seen in a single ended amp or True Class A push pull amplifiers like the designs of Lynn Olsen or the Sun Audio stuff or any number of Class A Push Pull designs out there.
Have Fun and Enjoy the Music
"Still working the problem"
We just go by the measurements...
If the tube does not cut off, its class A. If we drive the amp hard enough to make the tubes cut off, the amp is clipping a few watts earlier. IOW the tubes enter cutoff after the amplifier goes non-linear.
If the amp were to go into cutoff inside of its linear range, it would be a class AB2 amplifier. But it doesn't, instead that makes it class A2 according to the books.
The tube type is also very important. Its very difficult to ignore tube characteristics when designing any amp! If we used a pentode, this type of operation would not be so easy, not the least of which would be the grid current issue which is dramatically different then it is for a 300B or 6AS7G. 6C33s have a grid current character that is much closer to that of a pentode- these things can't be ignored even in theory.
Actually, the M60 is technically Class A all the way to 60watts. But that is only by definition and only because the 6as7g refuses to cutoff.
In a true Class A amplifier there is equal current above and below the idle point. Zero total current change. One bank going up by X amount while the other bank goes down by THAT SAME AMOUNT. This would be with linear tubes like the DHT's. Biasing is done at the center point of operation. If the tube is biased at 60ma. it will move up to 120ma and down to near zero with very little non-linearity in that movement. The current draw on the power supply will remain almost constant. What is described in this paragraph in not what is happening in the M-60 above 5watts.
On the Atkins site, while describing the Vox AC-30 guitar amp and whether or not it's Class A,
"There is an equal amount of current swing above and below the quiescent point, which indicates an average change in plate current of zero, which is another characteristic of a true class A amplifie" He shows some nice graphs that explains what I'm saying.
You are entitled to your opinion re used tube amplifiers, so in that case read the ad that appears alongside your post, for Transcendent amplifiers "15W to 80W", "starting at $1099". Transcendent should have something to suit your taste. Here is the law of physics you are up against: low number of output tubes results in high output Z in an OTL, making the low power output even less useful in that you will want to select a high-impedance speaker. So one solution to that conundrum is to use negative feedback (NFB) to reduce output Z. To some degree this is done in the Transcendent design. But there are some sonic compromises associated with excessive NFB or improperly applied NFB (not accusing Transcendent of either). No free lunch in other words.
I don't see what's wrong with buying a used tube amplifier, as long as you trust the other party's decription of the item (check their feedback on audiogon etc. - same as with any other item). I recently sold a pair of Atma-sphere M50 monoblocks in very good shape that would have been in your budget. Over the years, as much as 60% of the equipment I've purchased has been used, and I've never run into any insurmountable obstacles with the gear.
I suspect you're concerned with the tubes themselves, which with atma-spheres isn't as big a deal as you might imagine. Pretty much all of them use the rugged and reliable Russian 6AS7G power tubes and you can retube a pair of M-50 (or M-60s) with brand new Sovteks for about $240. Not that you'd have to, since they tend to last quite long. Best of all perhaps, the power tubes don't require any matching! Driver tubes (4 per chassis) particularly the stock factory ones are similarly inexpensive (though you could make them pricey by going with exotic NOS varieties). If you haven;t heard OTL's before, you probably in for a very special treat, and if I were you, I wouldn't discount the 'used tube gear' path to sonic nirvana.
I'm with you gentlemen; I cannot fathom the comments about used tube amplifiers. Maybe there is some validity when the equipment is 40 or 50 years old, but even then - if it was made with quality, it can be brought back.
As for Atma-Sphere in specific, I can say that buying a used piece of equipment is usually a very good idea. Frankly, there just isn't that much to go wrong with the equipment, and the way in which it's built (handwired, point-to-point) makes it very easy to update, upgrade or repair. With the power amps, as long as you still have a chassis and transformers,the service life of the equipment can be extended for generations to come.
Built-in obsolesence has never been a feature of Atma-Sphere equipment. Just ask one of the owners of original MA-2, who have amps running as full MA-2 Mk.II.3 equivalents.
What it comes down to is simple: We just have way too much pride in what we create to ever let it die of neglect or old age. We will always find a way to update or repair a piece, no matter how extensive the work. And we're always happy to help an enthusiastic new customer into the fold, by sprucing up an old piece they purchased elsewhere.
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