This here is an older amp - Ralph 09:58:09 07/16/12 (16)
 RE: This here is an older amp - den701 17:03:41 07/17/12 (15)
 RE: neutralizing rectifiers - Ralph 08:30:00 07/18/12 (14)

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 This here is an older amp - Ralph 09:58:09 07/16/12 (16)
 RE: This here is an older amp - den701 17:03:41 07/17/12 (15)
 RE: neutralizing rectifiers - Ralph 08:30:00 07/18/12 (14)
 RE: neutralizing rectifiers - den701 19:17:59 07/23/12 (13)
 RE: neutralizing rectifiers - den701 19:40:33 10/22/12 (12)
 Are all these upgreades? - tyu 13:44:30 10/23/12 (11)
 RE: Are all these upgreades? - den701 07:17:05 10/24/12 (10)
 RE: Are all these upgreades? - tyu 08:30:52 10/24/12 (9)
 RE: Are all these upgreades? - den701 07:02:39 10/25/12 (8)
 RE: Are all these upgreades? - tyu 08:28:40 10/25/12 (7)
 RE: Are all these upgreades? - Banat 11:46:47 10/25/12 (6)
 RE: Are all these upgreades? - tyu 12:44:06 10/25/12 (5)
 Sound that I looking for .... - Banat 13:08:39 10/25/12 (4)
 RE: Sound that I looking for .... - tyu 14:39:36 10/25/12 (3)
 RE: Sound that I looking for .... - Banat 16:12:15 10/25/12 (2)
 RE: Sound that I looking for .... - tyu 20:28:45 10/25/12 (1)
 RE: Sound that I looking for .... - Banat 00:18:59 10/26/12 (0)
 RE: M 60 MK2 PS and hexfred updates - Lew 07:01:38 07/16/12 (3)
 RE: M 60 MK2 PS and hexfred updates - den701 07:37:57 07/16/12 (2)
 RE: M 60 MK2 PS and hexfred updates - Lew 13:52:16 07/16/12 (0)
 RE: M 60 MK2 PS and hexfred updates - tyu 08:24:52 07/16/12 (0)
 RE: M 60 MK2 PS and hexfred updates - tyu 15:30:14 07/15/12 (0)
 RE: M 60 MK2 PS and hexfred updates - Banat 15:29:14 07/14/12 (0)
 RE: M 60 MK2 PS and hexfred updates - tyu 11:32:53 07/14/12 (30)
 RE: M 60 MK2 PS and hexfred updates - den701 09:57:56 07/15/12 (29)
 RE: M 60 MK2 PS and hexfred updates - Satelliteman 04:53:17 08/25/12 (0)
 RE: M 60 MK2 PS and hexfred updates - Banat 11:37:48 07/15/12 (27)
 RE: M 60 MK2 PS and hexfred updates - roio 22:42:44 09/12/14 (16)
 RE: M 60 MK2 PS and hexfred updates - Banat 03:28:00 09/15/14 (14)
 RE: M 60 MK2 PS and hexfred updates - roio 22:18:44 09/20/14 (12)
 RE: M 60 MK2 PS and hexfred updates - Banat 03:37:18 09/21/14 (11)
 RE: M 60 MK2 PS and hexfred updates - roio 06:12:04 09/21/14 (10)
 RE: M 60 MK2 PS and hexfred updates - Banat 06:23:07 09/21/14 (9)
 RE: M 60 MK2 PS and hexfred updates - roio 13:20:39 09/21/14 (8)
 RE: M 60 MK2 PS and hexfred updates - cpotl 19:34:44 09/22/14 (6)
 RE: M 60 MK2 PS and hexfred updates - roio 14:38:02 09/30/14 (5)
 RE: M 60 MK2 PS and hexfred updates - cpotl 16:12:12 09/30/14 (4)
 RE: M 60 MK2 PS and hexfred updates - roio 01:56:34 10/01/14 (3)
 RE: M 60 MK2 PS and hexfred updates - cpotl 05:02:53 10/01/14 (2)
 RE: M 60 MK2 PS and hexfred updates - roio 06:07:14 10/01/14 (1)
 RE: M 60 MK2 PS and hexfred updates - cpotl 08:29:26 10/01/14 (0)
 RE: M 60 MK2 PS and hexfred updates - Banat 15:46:47 09/21/14 (0)
 RE: M 60 MK2 PS and hexfred updates - roio 04:53:32 09/15/14 (0)
 RE: M 60 MK2 PS and hexfred updates - Banat 23:25:38 09/12/14 (0)
 RE: M 60 MK2 PS and hexfred updates - roio 07:38:49 09/12/14 (0)
 RE: M 60 MK2 PS and hexfred updates - den701 05:01:56 07/16/12 (1)
 RE: M 60 MK2 PS and hexfred updates - Banat 09:42:27 07/16/12 (0)
 RE: M 60 MK2 PS and hexfred updates - kbsp 15:24:06 07/15/12 (6)
 RE: M 60 MK2 PS and hexfred updates - roio 00:02:08 09/09/14 (0)
 RE: M 60 MK2 PS and hexfred updates - john65b 17:20:21 03/11/13 (4)
 RE: M 60 MK2 PS and hexfred updates - tyuu 09:29:00 03/12/13 (3)
 RE: M 60 MK2 PS and hexfred updates - john65b 09:47:45 03/12/13 (1)
 RE: M 60 MK2 PS and hexfred updates - tyuu 11:33:39 03/12/13 (0)
 RE: M 60 MK2 PS and hexfred updates - tyuu 09:32:11 03/12/13 (0)

• Schematic

• http://www.audioasylum.com/cgi/vt.mpl?f=otl&m=34354

• photo of the M-60 interior

Is this because you are not runing the Amps bal....?

But if well look at the speakers outputs here an in my amp in this MKll.3 a Zobel of a 7.5 ohm 5-10w an a 0.1 cap are on the outputs....

Is the Zobel OUT?...you did not wont the Zobel? or am i not seeing it in the pic....
An what are the res. across the pos..neg output sup caps in your pic?

Contrary to Zobel network where different combination of RC value relation can have bigger or less influence on Amp HF response and as result different reproduced sound from Amp/Speaker combo,
those two 600R resistors higher power capability hardly can have any influence on final reproduced sound .
As you already know they both serve only to made virtually ground point for output power (Circlotron) stage , actually in the same time they both serve for 6as7g tubes grid returning current path during A2 class of operation , and again they serve as 6as7g grid current limiting resistors , altogether with 6as7g grid stop resistors .
I have no doubt that Mr.Karsten have chosen the optimum resistors values
and power ratings for them .
Best Regards !

If I understand you correctly than you suggest to insert some 600 ohm power resistors across OTL Amp output terminals to balance the top end ? ,
Must say that there is no any logic to insert pure resistive load of 600 ohm across Amp output terminals ! , but hey man why not to try !!!, Who knows !!! :)
BTW I don`t use any original Atma-Sphere Amps , but now I use DIY OTL Circlotron Amps , which have very similar electrical concept as Atma-Sphere OTL , it is rated around 50W /32 ohms / Ch. ,
2 x 15 W is maximum power which I use for daily listening , for night listening I set them to around 2 x 0,5 W max. , I never shut off this Amps , day or night .
One more thing , regardless to Amps type I always use very big and very good internally dampened compression enclosures for 18`` bass drivers to get most precise and tight bass sound , in extra small boxes I use some German vintage fullrange ovals for mid`s , and those EV/CV combos for highs , speakers crossover network almost not exist , it is very simple network , just for highs and for mid`s speaker .

I have some serious difficulties to log-in and upload images on AA site , but first time when have chance to upload M60 schematics I will do that ,
any way your observation is correct that bias network is supplied Only from B-(2) and between ground point ,but Not between B-(2) and B+(2)and ground .

Salute !

thanks a lot for your inputs: I go to sign me up.

If you have listening experience with M60, could you say your impression when it is coupled to loudspeakers of 4 ohm or 8 ohm with no negative feedback?

If the power tubes are biased with the maximum allowed total current (0.8 A - 1.0 A), did you measure the maximum current driving the loudspeaker which is compatible with perfect sound? This parameter should characterise the amplifier, and it would be better assessed using 4 ohm loudspeaker, as it allows reaching more easily this maximum current while managing moderate sound level.
Sincerely
Roberto

Many thanks!

Sincerely
Roberto

Pure Class B regime by definition mean 0(zero) mA bias for output power stage (OPS) section, which in case of AT M60 will produce to much distortion regardless to connected load(speaker)nominal impedance , and is in the same time highly undesirable bias set up point for M60 OTL amp .
Normally M60 OPS is biased with 60mA per 6as7g (6h13c) triode section , which is 0,06A x 16 section = 960mA = 0,96A of total idle current.
Which also mean 0,06 A x 140VDC = 8,4W idle dissipation per OPS each triode section , or 8,4W x 16 section = 134,4W of total idle dissipation .

M60 OPS use sliding bias scheme , for example :
With inserted 4 ohm of load ( speaker) impedance OPS will work in AB2 class regime , with 8 ohm OPS will work in A2 class regime producing 60 W, but with 16 ohm M60 will produce 80W and in the same time output power tubes will run cooler and will last significantly longer .
But even nominal 32 ohm load(speaker) is an considerable good option for M60 OTL Amp .

Best Regards !

I not visit Tube Cad site for long time , and I don`t know who is that Stephen Kay , and basically that sentence `` Circlotron amplifier : .....`` mean really nothing to me .
------------------------------------------------------------
BTW , as I remember sometime and somewhere you can found suggestion that AT M60 OTL Amp not work in A2/AB2 regime but in AB1 class , which I consider as nonsense .
If you want to build AB1 class OTL Circlotron amp based on 6as7g power tubes than you need Totally Different design approach from AT OTL design .
For example : both B1/B2 OPS PSU`s need to be at least doubled in value , from 140VDC to 280VDC , but in the same time need to be reduced OPS each triode idle current value to 30mA ,just to get the same static Wa anode dissipation of 8,4W , and to obtain Wa to remain in SOA region which allow max 13W static dissipation for each 6as7g triode section .
Since this AB1 class OPS is now shifted in highly non linear region of dynamic operation next step what we need to do is to find the way how to reduce now both high level of produced THD and the OPS internal impedance .
Single way to do that is to implement gross level of GNFB ,but before that we need to design input VAS with min. 60 - 70 db of gain , which is in the same time and the amp open loop gain , just to allow to wrap around 35-45 dB of GNFB just to get decent amp with 25 dB of closed loop gain , and acceptable both low level of THD and amp internal resistance .
This above described design principle is not new , it is common for many Futterman based AB1 class OTL amplifiers ,and for many other OTL`s to ,
But it is Not common design principle for Atma-Sphere OTL amps .

And yes , I`m interested to see your measurements results and your conclusions .

Edit : Roberto I`m not consider myself to be a big expert ,I`m just profesional TV mehanicus ( I repair broken TV set`s for living ), but who sometime made some DIY stuff .

The article is actually by Jon Broskie. The remark is referring back to more extensive discussions he has given in previous articles, including the rather detailed one called Cars, Planes, and Circlotrons (linked on that same page (quoted above). Amongst other things, he makes the point that the power range for which the circlotron actually operates in class A is only up to the point where the output current reaches about twice the idle current. For power levels above that, the operation is essentially in class AB. The upshot is that except at rather low power levels, the operation of the circlotron is generally in class AB.

Chris

Of course, there is the very different question one could ask, as to whether an OTL sounds good when it is operating in class AB, and is the transition from class A operation at lower power to class AB at higher powers audible. I think it is generally agreed that OTLs tend to sound very good, even though they are mostly operating in class AB, and certainly my own experiences bears that out.

I'm not quite sure what double-blind listening tests one might usefully try, since a given amplifier is going to transition from A to AB at some specific power level. I suppose one could compare it at different idle bias levels, since that would alter the transition point. But it would alter lots of other things too.

Chris

I think John Broskie was making a gentle dig at some of the claims one occasionally encounters that some OTLs do succeed in operating fully in class A, and so within that context I think his usage of the idiom was not wholly inappropriate.

But I do agree that what really counts is how the amplifier actually sounds. In fact, it strikes me as being a pity that sometimes the essential point about how good the OTL sounds is in danger of being overshadowed by claims, that appear to lack justification, that it is operating fully in class A. There is actually nothing shameful about operating in class AB!

Chris