The amps operate and operated at the time in class A2. That is to say the tubes don't go into cutoff unless the amp is clipping, but they do draw grid current. This behavior is easily observed from the cathode resistors of the amp. So it appears he never made the measurement. This is not surprising if he also did not have a set of amps at the time.
Just so we are clear, class A2 offers greater power at some sacrifice of linearity. However in our design there are other factors that contribute greatly to reliability, bias stability and overload recovery, that easily overshadow the rather simple debate about class A2 vs A.
Again, I recommend that you try to circuit out rather than dis it on hearsay.
Finally, these comments are OT. If you wish to continue, start another thread and let me know.
That is simply not true.
Actually it is another example of marketing talk, suggesting "excellent sound quality because it is class A...."
, not unlike statements like "New class A" from Japanese manufacturers already long ago.If you don't get Broskie, I have another one for you, E.W.Fletcher and S.F.Cooke, 1951 - see attachment.
http://www.clarisonus.com/Archives/Amp_Design/Cathode_Follower_Amp.pdf
One quote in this article:
"...The maximum audio power output for the cathode-follower stage consisting of eight twin-triode 6AS7G tubes coupled to a speaker system of 16 ohms nominal impedance, where the limiting condition is class A operation, is I²*Rvc/2 = 16/2 = 8 watts......"
Clear enough that the eight tubes 6AS7G circlotron (not quite unlike the Atmasphere as it is functionally a cathode follower output power amplifier) would not manage much more than 4 watts pure class A in an 8 ohms load. (Physics has not changed (much) since 1951).
I don't suggest that the Atmasphere therefore is not a good amplifier; it certainly is.
The benign switching behaviour can make it an excellent AB amplifier (like Andrea's), but it certainly is not "60 watts class A" when driving normal speaker loads. That is my point.
And yes, let's leave the thread to Andrea.
I thought the Fletcher/Cooke cathode follower was not a real circlotron
but more a kind of special design to make one amp work like biamping, driving a 2way speaker
hence the lower output
btw, is it really a genuine circlotron if you have outputs connected to ground ?
or is this more a debate of true balanced cirlotron vs not balanced
I dont think 'ordinary' pushpull is the same as true balanced circlotron, is it ?
but more a kind of special design to make one amp work like biamping, driving a 2way speaker
hence the lower output
btw, is it really a genuine circlotron if you have outputs connected to ground ?
or is this more a debate of true balanced cirlotron vs not balanced
I dont think 'ordinary' pushpull is the same as true balanced circlotron, is it ?
When you take a close look at the first circuit of that amplifier you see a floating balanced output driving a normal 2-way crossover (second order high pass and low pass).
It is nothing special and has nothing to do with the output power capacity of the amplifier.
There is a dedicated "circlotron" website with nice information on history and the working principles, very interesting, and will probably answer your questions:
circlotron.tripod.com
The modern circlotron is OTL, with tubes or semiconductors.
Transformer coupled circlotrons have been made too in the past.
Bridged output and floating power supplies are properties of circlotrons.
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thanks, but I know all that
thats why i asked
and btw, the Fletcher/Cooke curcuit does not appear to have two seperate floating power supply
its 'just' a very clever cathode follower output, no ?
or are you saying that all cathode follower outout are circlotrons ?
oh, btw
don't forget the russian guys
there might be a good reason why they could good knowledge of tube OTL
through the past, plenty of tubes, and 'unobtainable'(expencive) transformers
but a different matter here
thats why i asked
and btw, the Fletcher/Cooke curcuit does not appear to have two seperate floating power supply
its 'just' a very clever cathode follower output, no ?
or are you saying that all cathode follower outout are circlotrons ?
oh, btw
don't forget the russian guys
there might be a good reason why they could good knowledge of tube OTL
through the past, plenty of tubes, and 'unobtainable'(expencive) transformers
but a different matter here
That's right, but I mentioned it to illustrate the class A - A/B issue (having the same type and number of output types as the Athmaspere).
In that respect it behaves like a circlotron.
Fletcher/Cooke circuit is totally different from floating Circlotron balanced bridge circuit .
BTW ,the real question for Atmasphere OTL Circlotron power amps actually is : How much A1 class power this amps can produce , and how much A2 class power can produce, loaded with adequate relative higher load(speaker ) impedance .
since this OTL Circlotron power amps loaded with inadequate relative low(load) speaker impedance slide in AB1/AB2 class of operation easy .
After all is not easy at all to drive this paralleled low Rp 6as7g triodes in A2/B2 class of operation and to obtain Circlotron output power stage stability , except with adequate designed DC coupled drivers units like is done in Atmasphere amps .
Think this is the real questions which usually cause to confuse people .
Best Regards for all !
BTW ,the real question for Atmasphere OTL Circlotron power amps actually is : How much A1 class power this amps can produce , and how much A2 class power can produce, loaded with adequate relative higher load(speaker ) impedance .
since this OTL Circlotron power amps loaded with inadequate relative low(load) speaker impedance slide in AB1/AB2 class of operation easy .
After all is not easy at all to drive this paralleled low Rp 6as7g triodes in A2/B2 class of operation and to obtain Circlotron output power stage stability , except with adequate designed DC coupled drivers units like is done in Atmasphere amps .
Think this is the real questions which usually cause to confuse people .
Best Regards for all !
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Looking at the curves of the 6AS7G this is a tube that will not tolerate much grid current without high distortion; class A2 is not at stake here IMO.
No is not comparable , since the output power stage internal impedance is not the same for both circuit topology .
Yes it is true but for 6as7g anode follower based circuits , but is not valid for 6as7g cathode follower circuits which work with inherently 100% of local negative feedback .
Circlotron circuit is formed from two independent CF unit joined together so A2 class of operation give inherently relative low open loop distortion .
BTW A2 class of operation is by definition A class to .
Then give us an idea how different the output power stage internal impedance of the circlotron is from for example the Fletcher/Cooke type of amplifier, and how much effect this might have on class A output power.
Facts please, not vague statements.
I don`t want to abuse this great topic started by respected DIY member Audiodesign going to much off topic ! , but If you read this article carefully you well found the answer : 6C33C-B OTL Amplifier - Background and OTL Circuits
Banat,
The push pull OTL amplifier by Fletcher/Cooke has 23,67 ohms output resistance; the load is 14,22 ohms. Pure class A output power a little over 6 watts with 8 6AS7G tubes.
Please note that this amp was designed to be a class A amp (driver stage).
This output resistance is almost the same as for the push pull OTL amplifier in the article you provided (6C33C....Background and OTL circuits) which makes sense as 8 6AS7G's are about the same as 4 6C33C's, 27 ohms.
The circlotron with 4 x 6C33C has output resistance of around 10 ohms.
I have a building instruction for the Atma-Sphere MA60II here (by John Harper).
He measures an output resistance of 10 ohms; sounds believable with 8 6AS7G's.
Harper measures low THD (mostly even order) up to 10 watts; above 10 watts distortion sharply rises with odd orders coming in; IMO switching from class A to class B at around 10 watts.
So we have PP OTL with 23,67 ohms Ri into 14,22 ohms load, giving 6,3 watts class A.
We have Circlotron OTL with 10 ohms Ri into 8 ohms.
Would it give 60 watts class A? I think not (with 550mA of idle current it will be some 5 watts pure class A).
A well constructed MA60 will be an excellent sounding class AB amplifier, no doubt regarding the excellent reviews.
I propose end of discussion in order not to hijack this thread any further.
When our member Atmasphere likes to comment, my suggestion is to open a new thread.
The push pull OTL amplifier by Fletcher/Cooke has 23,67 ohms output resistance; the load is 14,22 ohms. Pure class A output power a little over 6 watts with 8 6AS7G tubes.
Please note that this amp was designed to be a class A amp (driver stage).
This output resistance is almost the same as for the push pull OTL amplifier in the article you provided (6C33C....Background and OTL circuits) which makes sense as 8 6AS7G's are about the same as 4 6C33C's, 27 ohms.
The circlotron with 4 x 6C33C has output resistance of around 10 ohms.
I have a building instruction for the Atma-Sphere MA60II here (by John Harper).
He measures an output resistance of 10 ohms; sounds believable with 8 6AS7G's.
Harper measures low THD (mostly even order) up to 10 watts; above 10 watts distortion sharply rises with odd orders coming in; IMO switching from class A to class B at around 10 watts.
So we have PP OTL with 23,67 ohms Ri into 14,22 ohms load, giving 6,3 watts class A.
We have Circlotron OTL with 10 ohms Ri into 8 ohms.
Would it give 60 watts class A? I think not (with 550mA of idle current it will be some 5 watts pure class A).
A well constructed MA60 will be an excellent sounding class AB amplifier, no doubt regarding the excellent reviews.
I propose end of discussion in order not to hijack this thread any further.
When our member Atmasphere likes to comment, my suggestion is to open a new thread.