The 115+115/15V+15V is bad anyway.
When the secondaries are paralleled we have a 15,3:1 voltage ratio, that is 1880k(a-a) : 8 ohms, a much too high primary impedance for a couple of 6C33's in PP.
When the secondaries are connected in series we have a 7,67:1 voltage ratio, that is 470 ohm primary impedance to 8 ohm, way too low (and the secondary will have rather high DCR which is not good for damping).
A 2x20V paralleled secondary would be better, giving some 1K a-a impedance to 8 ohms.
Core saturation would depend on core dimension to see at what frequency and power that would occur.
Shoog's operating point of 100V/250mA is really miserable when checking the 6C33 curves.
The grids are at about - 25 V, so less than 20 VRMS grid voltage per tube is available for class A.
In the PP amp no more than about 80 VRMS would be produced, leaving us with a power of no more than 4 watts at 8 ohm with the toroid in 115+115:15//15 mode, or 14 watts with high distortion and bad damping (secondaries in series).
A single ended 2A3 would be about as powerful, but with 20 watts of total dissipation in stead of some 120 watts for the 6C33 PP.
When the secondaries are paralleled we have a 15,3:1 voltage ratio, that is 1880k(a-a) : 8 ohms, a much too high primary impedance for a couple of 6C33's in PP.
When the secondaries are connected in series we have a 7,67:1 voltage ratio, that is 470 ohm primary impedance to 8 ohm, way too low (and the secondary will have rather high DCR which is not good for damping).
A 2x20V paralleled secondary would be better, giving some 1K a-a impedance to 8 ohms.
Core saturation would depend on core dimension to see at what frequency and power that would occur.
Shoog's operating point of 100V/250mA is really miserable when checking the 6C33 curves.
The grids are at about - 25 V, so less than 20 VRMS grid voltage per tube is available for class A.
In the PP amp no more than about 80 VRMS would be produced, leaving us with a power of no more than 4 watts at 8 ohm with the toroid in 115+115:15//15 mode, or 14 watts with high distortion and bad damping (secondaries in series).
A single ended 2A3 would be about as powerful, but with 20 watts of total dissipation in stead of some 120 watts for the 6C33 PP.
Hi,
It is of no use to show how it would work bad Pieter. It can work high-end a question of the right dimension.
It is only interesting to know how it would work perfect. Then we need some one who knows something about transformers. Shoog do you know what would be best transformer and optimal working point?
Or maybe others can tell how to use a low cost toroidal power transformer. I will ask a colleague who designs power supplies if there is a save way to choose the right transformer without saturation problems. I am not sure about max voltage and saturation problems.
And what Pieter says about series secondary is the worst thing to do if you want to have maximum performance at HF output. Every one who can calculate a parallel coil and cutoff can in fact that simple.
It is of no use to show how it would work bad Pieter. It can work high-end a question of the right dimension.
It is only interesting to know how it would work perfect. Then we need some one who knows something about transformers. Shoog do you know what would be best transformer and optimal working point?
Or maybe others can tell how to use a low cost toroidal power transformer. I will ask a colleague who designs power supplies if there is a save way to choose the right transformer without saturation problems. I am not sure about max voltage and saturation problems.
And what Pieter says about series secondary is the worst thing to do if you want to have maximum performance at HF output. Every one who can calculate a parallel coil and cutoff can in fact that simple.
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I was talking each section which at 100V 500mA per valve stays within the 50W recommended max dissipation for both sections in parallel.
Last time I checked the secondaries of a toroidal were well below 1R and so damping isn't really a major issue here. Using local feedback an amp like this can achieve an ouput impedance around 50R or lower, which should be about the best you can get without resorting to massive amounts of global feedback.
In the end this would produce efficiency in the range of an SE, which is fine by me considering it will be pure class A.
Personally I wouldn't build it because I can achieve all that such an amp can give me using 6080's and half the power consumption. Given the right speakers an amp like this can achieve miracles with just 6W of output.
Shoog
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Very good point. The 6C33C can take a lot of current. That's why 6C33C have reason to be utilized in OTL, rather than in OT type amps. If not losing bandwidth, then transformers tend to lose at least detailness from sound. With modest budget one can build a very good OTL amp. With same sound qualities there are needed a lot of tricks to be done with high current OT trafos (=not modest priced), capable to give sound good enough with 6C33C. Output power will be in same class for both situations. I can not see any reason to love those output transformers.
When I understand right you say OTL is better at detail and overall sound is preferred to a transformer output.
I do not think you can state that with measurements to prove it. Probably is the OTL sensitive to load behaviour and cause false detail . And a transformer type will have more control and there for maybe considered less detailed.
Personally I do not believe detail is gathered with bandwidth, the bandwidth indicates good behaviour at the frequencies we can hear in the midrange.
Exactly, "the right dimension".
This means well chosen operating points, not what Shoog comes up with.
Shoog, 100V 500mA is what the 6C33 can do as a pass tube in a regulated power supply.
Did you ever check triode curves of the 6C33 when used for audio?
Ever heard of load lines?
My suggestion is to learn a bit more on tube basics.
I try to work out a simple way to select the right toroidal for the DIY community here. My colleague has to think himself how it worked, with integrals.
Although he did nothing else at studying university.
Probably is a max current saturation test the most simple way.
See my earlier post: 115+115V:20+20V would give you some 1k primary impedance to 8 ohms, which would be fine for a pair of 6C33's in PP.
But the toroidal (power supply) transformer will give you only the correct step-down ratio, and therefore the correct load; in other respects it does not resemble a good audio output transformer.
When you don't take measures to prevent DC unbalance in the primary of the output transformer, the toroidal core will easily saturate which you might not notice but will cause sound quality to suffer.
Preventing DC unbalance with 6C33's will be a hell of a job; when you think you can do this by some simple pot, forget it. You must think of some kind of servo to handle this; this is a drawback of the 6C33 being that high transconductance.
I have no experiences with 6c33 it seems a nice tube, my reply was a quick calculation on the idea to use a standard toroidal. It is a other thing to work it out in detail.
Eyeballing the curves and that operating point would work. If it came to designing such an amp - I would design backwards from such a point.
50R was a reference to the rp of the 6c33c in that operation. Final output resistance would be somewhat different.
Before we started all this pointless bickering, I was responding to the suggestion of going OTL. I think OTL represents a brute force OTT approach which can be matched more efficiently with an OT design. The choice of Toroidals allows that and avoids the penalties usually associated with a PP OT's. Keeping DC out of the transformer is not that difficult to achieve and will bring benefits to the overall performance. What some see as the problems of toroidals, I see as the advantages which just need a little latteral thinking to overcome. It allows for design of fully differential amps from from end to finals - and if you have listened to an amp of this type - you will realise its well worth the extra effort.
A number of people have followed this design approach and built amps which have sent at least two 300B SE amps into an early retirement.
Ultimately its your own choice what you build - but I put it out there that there is a third way other than SE and OTL - and I personally think its a better way.
Shoog
50R was a reference to the rp of the 6c33c in that operation. Final output resistance would be somewhat different.
Before we started all this pointless bickering, I was responding to the suggestion of going OTL. I think OTL represents a brute force OTT approach which can be matched more efficiently with an OT design. The choice of Toroidals allows that and avoids the penalties usually associated with a PP OT's. Keeping DC out of the transformer is not that difficult to achieve and will bring benefits to the overall performance. What some see as the problems of toroidals, I see as the advantages which just need a little latteral thinking to overcome. It allows for design of fully differential amps from from end to finals - and if you have listened to an amp of this type - you will realise its well worth the extra effort.
A number of people have followed this design approach and built amps which have sent at least two 300B SE amps into an early retirement.
Ultimately its your own choice what you build - but I put it out there that there is a third way other than SE and OTL - and I personally think its a better way.
Shoog
I presume you did not understand my statement right. I see generally any transformer in signal path is doing no good. Transformers in signal path are not used because of good life. Topic here is: are 6C33C tubes capable for making an amp. My statement is: yes they are. Actually they are capable for very a good OTL using. And 6C33C OTL is giving better sound by all means: rich and fast basses, cristal clear highs and singing mids, exact details. My first experience with 6C33C in OTL gave absolute linear 16Hz-40kHz (my sinewave generator will not go lower than 16Hz). 15W@8 Ohm continuos sine power per channel. These are actual values.
It is possible to get play without the OT when using 6C33C. Get rid of the OT - the most distorbing component in whole sound signal path.
Actually the situation is exactly 100% other way.
I agree with this. Details are there, in records. Just the damn OT kills them.
I would agree with your statement generally regarding OT's, but as others have pointed out - not all OT's are equal, and some statements only apply to some particular OT's.
There are definate practical reasons why some OT's will lose detail and sound mushy in the bottom - but this is not implicit in all OT design.
Toroidals and C-cores are very different beasts to EI's, and those who have used them report a very different experience to yours.
Shoog
There are definate practical reasons why some OT's will lose detail and sound mushy in the bottom - but this is not implicit in all OT design.
Toroidals and C-cores are very different beasts to EI's, and those who have used them report a very different experience to yours.
Shoog
Peace, man!
I'm not the carrier of the Absolute Truth, of course. Just sharing some late positive experience.If I'd look to 6C33C OT, I would look at this Cinderella schematic. The article is in russian, probably some translator s/w will help.
The main idea is to compensate out the magnetic field from SE output transformer core, caused by anode current. It helps to clear the lower end. And the anode current for 6C33C is not the smallest one as we know. Fixed bias, as I like it.
Impressive one can read russian all consonatsPeace, man!
If I'd look to 6C33C OT, I would look at this Cinderella schematic. The article is in russian, probably some translator s/w will help.
The main idea is to compensate out the magnetic field from SE output transformer core, caused by anode current. It helps to clear the lower end. And the anode current for 6C33C is not the smallest one as we know. Fixed bias, as I like it.
i need some help. I m building a 6h6p&6dj8 + 6c33 SE...
I have a toroid. transf. for heaters: 12V 100 va out.
6h6p & 6DJ8 want 6.2 volt, 6c33 (series) 12V. All of this tube have insulated from ground heaters ( no joint in the middle ).
Now i use to connect directly transformers to 6c33. Where put magical resistors for grounding heater ? Can i use a rect bridge and a LM317 in order to bring down the voltage at 6.3 ? For grounding it ?
I have a toroid. transf. for heaters: 12V 100 va out.
6h6p & 6DJ8 want 6.2 volt, 6c33 (series) 12V. All of this tube have insulated from ground heaters ( no joint in the middle ).
Now i use to connect directly transformers to 6c33. Where put magical resistors for grounding heater ? Can i use a rect bridge and a LM317 in order to bring down the voltage at 6.3 ? For grounding it ?
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