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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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PostPosted: 31 Jan 2018, 16:24 
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The problem is,

The bias type and bias current change how the tube sounds in operation.
The same as whatever is in the cathode circuit. I found the 6c33c to be very variable with sound dependant on both bias current and applied voltage.
So this isn't just about distortion, the 6c33c also changes sound over a couple of days after first power up. The idle current also changes over about 24 hours and is tube dependant. ie not always consistent.

As a reflection the 211 used in the Ongaku sounds rubbish if the voltage is to low irrelevant of bias current.
Where the 845 is happier at higher current lower voltage.
So there is much more than just design and distortion.

Even the rectifier type in the circuit changes the sound character. There is always more.

Regards
M. Gregg

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Last edited by M. Gregg on 31 Jan 2018, 16:30, edited 1 time in total.

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PostPosted: 31 Jan 2018, 16:29 
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Well in theory the constant current load would keep the bias 100% dependant of the constant current load, during heating up or weak valves, its only the cathode voltage that would change becuase the load line changes when heating up (grid to cathode voltage for given plate votlage and cathode current).

Quote:
Even the rectifier type in the circuit changes the sound character. There is always more.

Yes I've tried this before with my pre amp :D


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PostPosted: 31 Jan 2018, 16:36 
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KochiyaYamato wrote:
Well in theory the constant current load would keep the bias 100% dependant of the constant current load, during heating up or weak valves, its only the cathode voltage that would change becuase the load line changes when heating up (grid to cathode voltage for given plate votlage and cathode current).


The CCS will effect the sound character of the amplifier. as it does within the cathode of a tube.
People go out of their way to redesign CCS and try hundreds of circuits to try to improve and reduce the effect.
The effect is such that some people build valve/tube circuits because they don't want the sound to be effected by SS parts.
Now if you think this is not the case or that FB can disguise it, then others will argue that FB removes information from the audio signal.
Its why some designs look strange or don't make sense.

Later...

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M. Gregg

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PostPosted: 31 Jan 2018, 16:52 
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I accept ccs and bias current changing the sound of a 6c33c.

In my design testings, transistors amplifier with more feedback and distoriton gives me more detail and better overall sound. Valve preamps I've design also heads the same way, it gets warmer and prettier because I'm left with only valve taste. The zero negative feedback valve pre amp or transistors amps I've tried gave me harsh sounds because of the distortion existing.

Today virtually all sound sources come from some sort of transistor amp.

My experience is NFB amps are much harder to design and get right, you get high frequency oscillations and distorted square wave outputs when the high frequency compensation is not done correctly or if the schematic is poor.

I'm going to repost my schematic, if any one wants to hear more I will go into detail.
Personally I don't see the ccs adding much or any transitor into the sound, reason is becasue the output signal taken dosen't travel in series through any transistor.

I'm editing for a bit more, I've used excat same schematic in my pre amp designs but with diffrent values of emitter resistor and non darington pass transistor, it worked perfectly as a constant current load. I've tried ef183 in place of a 12ax7 as cathode follower, same current both cases, about 8-10v more volts with EF183 because the ef183 has a diffrent load line. The grid is connected directly to previous stages with some dc. The diode in the schmeeatic is actually a LED with foward voltage of 1.8V yellow or red.
Extra 8-10v at cathode meant that my CCS expriences 8-10v extra load slightly hotter.


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Last edited by KochiyaYamato on 31 Jan 2018, 18:04, edited 5 times in total.

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PostPosted: 31 Jan 2018, 17:40 
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I know what my money is on.

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PostPosted: 01 Feb 2018, 03:08 
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a) Haven't read much (almost nothing :| ) of this thread, but just a crazy idea, or maybe just an idea. I am assembling the 2SK1058 single-transistor amp, that uses a single transistor with a huge resistor loading the drain. Replacing the resistor for an active load (CCS) could possible result in ..."something".
SO, could you make a CCS of another 6S33S? Besides, you say that no signal passes through a transistor, which isn't that correct as you feed your speakers with AC, that is partly (50%) controlled by the tube and partly (the other 50%) controlled by your CCS.

b) Playing most of my music through a single dual-triode, 5998A, I am intrigued by powerful dual triodes like 6AS7G, 6080, 6336 and so on and thought that maybe 6S33S could ... SH|T!, its a single triode. Forget it!

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PostPosted: 01 Feb 2018, 04:38 
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Yes I am more than happy to make a ccs for your amp. I may even make a turotrail on designing your own ccs. Once you know the basics and know lots of building blocks things become very easy.

The reason on why no signals pass through the ccs is firstly simply because no signal flows in series from signal to output.
Signal goes from grid of 6c33c, the grid controls the cathode voltage and the cathode voltage is totally dependat on grid voltage. You see now a 10v increace on grid, means 10v increase in cathode voltage given the load line stays at the same point. Practically the load line changes and this means distortion.
This change in voltage is then passed through a couppling capacitor to speaker, simple.

Same with transistors, the basic principle and applys nearly in all cases.

For transistors the emitter voltage is 100% dependant on the base voltage, emitter voltage is always 0.6v to 0.7v lower than base vbe drop.
This means if you fix the base voltage with a led or precision voltage refrence, the emitter voltage stays constant. Because the emitter voltage is constantly set to a known voltage, one can use V=IR and find resistor for desired current that the transistor will operate.
The emitter of the CCS is set at a known constant level above ground, putting a resistor allows the transistor to have a return path and have constant current. The constant votlage accross the resistor is known and V=IR applys in all electornics.

Now the collector of the resistor is the non dependant point of a transistor. The Emitter is a depenant voltage point in a transtor purely controled by base.
This means the collector voltage at the transistor is controled by external sources, in a CCS emitter or cathode follower this point is then controled by the cathode or emitter of another device.

Because there isn't any more extrenal components acting at the Constant Current Load collector and cathode of 6c33c, the voltage at this point will purely be depentant on the grid voltage of 6c33c.

The collector is a non depenant point because the transitor it self cannot control the votlage level at its own collector. This voltage is set by external sources.
Same for the plate of a valve.

The case where the emitter or cahthode voltage is not dependant on grid or base anymore is when you have external current sources, or external emitter junctions connected to this point
In this case the calculations get more complex and I my self is not expreince in this area.

I'll leave it here with an explnation, I will look into desiging one for your mosfet amp maybe 12-48hours later, Its currently 10:38 at night in New Zealand and its end of the day

It will be helpfull if you tell me your power targer class A into a 8 or 4 ohms and target idle current you are looking at


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PostPosted: 01 Feb 2018, 06:00 
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No no no, thanks for your offer, but not now, I have no need for CCS right now. I thought for a short moment the 6S33S was a dual triode and dual triodes are funny stuffs as you can build simple amps - my 5998A-SE.
Also I want to keep things simple, though I am sometimes looking att CCS to use for driver tubes, but have no immediate need.

The single-transistor amp is based om the 2SK1058 (EoZ), described in the projects department. I think that a FET-CCS could be used instead of the resistor, but things would still run hot.

But at the moment, no need, but I will still watch how your projects evolves and talking of cathode folloewrs, I have a half-built 6V6-SE with the OP transformer loading the cathode.

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PostPosted: 01 Feb 2018, 17:10 
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Maybe a 6C33C with CCS should have its own thread and leave this thread to the original concept. Might be time to replant it.

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PostPosted: 01 Feb 2018, 18:50 
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Soundbrigade wrote:
The single-transistor amp is based om the 2SK1058 (EoZ), described in the projects department. I think that a FET-CCS could be used instead of the resistor, but things would still run hot.

20w accross a CCS is hotter and more expensive than a 20w resistor

mwhouston wrote:
Maybe a 6C33C with CCS should have its own thread and leave this thread to the original concept. Might be time to replant it.

I'd look into that If I buy some 6c33c and do a test circuit to check everything works. I'm not sure if its a good thing to make a thread on a schematic that is not gauranteed to work.
In theory it will work.


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