Hi to all,
As you know from my previous post I'm new to this hoby of ours. This is my first try on design. I choose to start with SE. The 300B as output and mu topology in a driver stage.
I have read few books and some articles on the WEB about SE design with 300B. I have also seen so many designs with plate voltage of 425V. That's vhat make me confused.
I do understand that with increase in plate voltage one can get more PO, but operating 300B at this voltage is very close to the cutoff region that practicaly there is very small voltage sving on the negativa side of cycle. Also, in those same designs people are using OPT with primary impedance of 2K5 to 3k0. This makes a load line very steep. This all makes me wander if the goal is to operate walve in most linear region with biger voltage sving (les power at output) or is the power more important than voltage sving.
One more question, what determines impedance of the primary of the OPT (how do you choose impedance). Does any parametar of the walve dictates choice of impedance and if thet's the case, how? I think this have something to do with output impedance of the stage but I'm not certain about this.
Please help me start on the right track. My goal is to build this amp but more importantly to learn from ground up.
Thank you.
P.S. English is not my mother tonque so please bear with me.
As you know from my previous post I'm new to this hoby of ours. This is my first try on design. I choose to start with SE. The 300B as output and mu topology in a driver stage.
I have read few books and some articles on the WEB about SE design with 300B. I have also seen so many designs with plate voltage of 425V. That's vhat make me confused.
I do understand that with increase in plate voltage one can get more PO, but operating 300B at this voltage is very close to the cutoff region that practicaly there is very small voltage sving on the negativa side of cycle. Also, in those same designs people are using OPT with primary impedance of 2K5 to 3k0. This makes a load line very steep. This all makes me wander if the goal is to operate walve in most linear region with biger voltage sving (les power at output) or is the power more important than voltage sving.
One more question, what determines impedance of the primary of the OPT (how do you choose impedance). Does any parametar of the walve dictates choice of impedance and if thet's the case, how? I think this have something to do with output impedance of the stage but I'm not certain about this.
Please help me start on the right track. My goal is to build this amp but more importantly to learn from ground up.
Thank you.
P.S. English is not my mother tonque so please bear with me.
Best of luck on this project- it's a little like starting to do carpentry by building an apartment house.
Understanding load lines is important here. Morgan Jones gives a fine illustration in his Scrap Box Challenge design ("Building Valve Amplifiers"), one well worth studying before tackling a design.
Understanding load lines is important here. Morgan Jones gives a fine illustration in his Scrap Box Challenge design ("Building Valve Amplifiers"), one well worth studying before tackling a design.
loadlines
Steve Bench also has a nice tutorial on his site:
http://members.aol.com/sbench102/po-dis.html
Steve Bench also has a nice tutorial on his site:
http://members.aol.com/sbench102/po-dis.html
300B anode characteristics from Audiomatica for reference:
I don't like the 300B but that's just my own prejudice
What makes you think that? If you look at the curves above, 425Vak, -75Vgk is in the middle of the linear part of the curve - far away from cutoff. Of course operating at 425Vak and -125Vgk is a different matter....
With triodes, generally the higher load Z and higher supply voltage, the lower distortion. The circuit designer has to trade off between power output and distoriton.
Sometimes it's just what you have on hand... There is a rule of thumb to say it should be 2-3 times the ra of the valve, though.
A thorough read of the linked page from Steve Bench's site above will help greatly here.
Your English is just fine
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MlinarS said:
I don't like the 300B but that's just my own prejudice
MlinarS said:
What makes you think that? If you look at the curves above, 425Vak, -75Vgk is in the middle of the linear part of the curve - far away from cutoff. Of course operating at 425Vak and -125Vgk is a different matter....
MlinarS said:
With triodes, generally the higher load Z and higher supply voltage, the lower distortion. The circuit designer has to trade off between power output and distoriton.
MlinarS said:
Sometimes it's just what you have on hand... There is a rule of thumb to say it should be 2-3 times the ra of the valve, though.
A thorough read of the linked page from Steve Bench's site above will help greatly here.
MlinarS said:
Your English is just fine
Re: Re: Newbie needs clarification
I'd go one step further. Make a few copies of the 300B plate curves, grab a pencil and straight edge and follow Steve's instructions step by step, including the calculations. Make sure you try few variations on the load lines.
I'm a real newcomer to this tube stuff and electronics in general. I read all I can, but using my hands, doing the calculations, and seeing the relationship between lines, power, and distortion, really gets the concepts down for me.
Sheldon
audiousername said:
I'd go one step further. Make a few copies of the 300B plate curves, grab a pencil and straight edge and follow Steve's instructions step by step, including the calculations. Make sure you try few variations on the load lines.
I'm a real newcomer to this tube stuff and electronics in general. I read all I can, but using my hands, doing the calculations, and seeing the relationship between lines, power, and distortion, really gets the concepts down for me.
Sheldon
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