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 Post subject: GU-50 Single Ended Amplifier Design
PostPosted: Sun Oct 31, 2010 8:20 am 
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Hi everyone,

After looking at the Wavebourn Pyramid Amplifiers, decided to make one myself, but in single ended. Smile
Any thoughts for a driver suitable for this?


 
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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Sun Oct 31, 2010 8:24 am 
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quikie22 wrote:
Hi everyone,

After looking at the Wavebourn Pyramid Amplifiers, decided to make one myself, but in single ended. Smile
Any thoughts for a driver suitable for this?

Ask Wavebourn directly. He is here. Good luck!

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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Sun Oct 31, 2010 10:08 am 
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I am busy now, I will post later. In short, I will use 6N1P and 6P15P tubes in driver, both will be loaded on gyrators. Another option is to use 6N16B instead of 6N1P, but I don't have them yet. I've ordered 2.5K output transformers from Edcor USA, but forgot to order plate filter chokes, so will build without them, then add them later.

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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Sun Oct 31, 2010 3:51 pm 
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6N1P and 6P15P sounds like a good idea. I have the 6N1P but I have the 6P14P instead of the 6P15P. So it is very possible that 6P14P will be the driver that I will use. In my Aikido line stage amplifier, I find the 6N1P sounds better than 6922, so I have been considering it for my front end.
How did you configure your 6P15P biasing scheme? Why do we want to use a gyrator instead of simple resistive loading? Better low frequency response?


 
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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Sun Oct 31, 2010 4:32 pm 
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Joined: Tue Feb 10, 2004 12:30 pm
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For 6P14P you will need different bias voltage.
To figure out how to use it you can find and examine anode curves.

Here are examples:

Image

Here is 6P14P graph I found googling for the picture:

Image


Imagine load line and see how similar / different are distances between points where load line crosses curves. The less is difference between values of currents, the more linear will be the stage.

You can see that the higher is load resistance, the more linear is the result.
Increasing load resistance you have to increase B+ in order to keep idle current you need. If to load the stage on a plain resistor such increase means higher power dissipation on the resistor, and it has limit: tubes can't be used when possible anode voltage exceeds their ratings.

Gyrator is a converter of one reactive resistance to another. In our case it converts capacitive resistance to inductive one. Using gyrator we can keep idle voltage on anode in selected range, while it's dynamic resistance will be huge. The higher it is, the less distortions we get that are caused by dependence of internal resistance of triode on anode current.

I.e. the purpose of gyrator is to get less possible distortions, while keeping anode voltage less dependent on cathode emission that depends on tube brand, age, constructive differences, temperature of cathode that depends on filament voltage and it's resistance.

I select idle current 30 mA, anode voltage 200V. Such regime allows me to get 200V peak to peak to drive grid of GU-50 tube that is twice higher than minimally needed. As you can see such regime corresponds to 4.8V first grid bias. It is exactly what I can get from 2 LEDs in series. Since 30 mA exceeds maximum 20 mA for LEDs, I need 4 LEDs connected in series/parallel.

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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Sun Oct 31, 2010 6:10 pm 
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So in other words we get higher linearity with a gyrator and also "less heat from resistor" and and less need for a high B+.... that sounds perfect. But it does seem we need high voltage MOSFETs and Transistors. I have some IRF840 MOSFETs, can I use those? What about the bipolar transistors, what are the other option I have? What should the max ratings be for the Solid State components be?
Also from Klausmobile, seems he has a curve for the EL84 (similar to 6P14P). I guess I will use that curve. Very Happy


 
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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Sun Oct 31, 2010 6:30 pm 
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quikie22 wrote:
So in other words we get higher linearity with a gyrator and also "less heat from resistor" and and less need for a high B+.... that sounds perfect. But it does seem we need high voltage MOSFETs and Transistors. I have some IRF840 MOSFETs, can I use those? What about the bipolar transistors, what are the other option I have? What should the max ratings be for the Solid State components be?
Also from Klausmobile, seems he has a curve for the EL84 (similar to 6P14P). I guess I will use that curve. Very Happy


Yes, he has a nice curve tracer and did a great job!

Yes, IRF840 can be used to load 6P14P. I'll draw schematic later as soon as have some time to do that.

To load 6N1P I would use some MOSFETs or bipolar transistors with much lover capacitances. I have a bunch of Philips BSP225 that I use there. They are SMD, but big enough to solder.

Gyrator works similarly to a choke, except it does not store an energy so can't provide voltage swing greater than B+. That's why for 200V on anode B+ should be 300 or more volts.

Max ratings for solid state components are obvious: breakdown voltage greater than possible B+ value, max current higher than expected, and power dissipation on possible temperature in the safe area. Also, lower capacitances and higher transconductance. I.e. requirements are the same as for CCS load. A good option is cascode: small fast high gain transistor that controls the current, and higher voltage/higher power counterpart.

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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Mon Nov 01, 2010 12:32 am 
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Posts: 238
Cool. I will wait with great anticipation for the gyrator circuit. I will take the B+ voltages into consideration if using the gyrator. So minimum of 300V for driver side. It is a bit difficult to get high voltage transistors here. They usually have irf840 but I will try to find if there are others. I think the IRF820 should do for lower Miller capacitance and still meet the B+ requirements.


wavebourn wrote:
Yes, he has a nice curve tracer and did a great job!

Yes, IRF840 can be used to load 6P14P. I'll draw schematic later as soon as have some time to do that.

To load 6N1P I would use some MOSFETs or bipolar transistors with much lover capacitances. I have a bunch of Philips BSP225 that I use there. They are SMD, but big enough to solder.

Gyrator works similarly to a choke, except it does not store an energy so can't provide voltage swing greater than B+. That's why for 200V on anode B+ should be 300 or more volts.

Max ratings for solid state components are obvious: breakdown voltage greater than possible B+ value, max current higher than expected, and power dissipation on possible temperature in the safe area. Also, lower capacitances and higher transconductance. I.e. requirements are the same as for CCS load. A good option is cascode: small fast high gain transistor that controls the current, and higher voltage/higher power counterpart.


 
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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Mon Nov 01, 2010 6:47 am 
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Шаман, типа...

Joined: Tue Feb 10, 2004 12:30 pm
Posts: 7312
Location: Pleasant Hill, California
quikie22 wrote:
Cool. I will wait with great anticipation for the gyrator circuit. I will take the B+ voltages into consideration if using the gyrator. So minimum of 300V for driver side. It is a bit difficult to get high voltage transistors here.


Where do you live? I can share some BSP225 in envelope.

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А женщина даже в мужской рубашке выглядит гораздо приличнее, чем мужчина в женских колготках! Be-be-be!


 
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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Mon Nov 01, 2010 7:45 am 
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Sadly I stay far far away. I believe the postage will cost quite a bit. I am from a place called Malaysia. It is located just south of Thailand (Siam). I don't mind paying for the postage charges though I suspect the time taken to arrive might be unpredictable.

http://maps.google.com.my/maps?client=s ... CBgQ8gEwAA


 
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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Mon Nov 01, 2010 7:47 am 
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Шаман, типа...

Joined: Tue Feb 10, 2004 12:30 pm
Posts: 7312
Location: Pleasant Hill, California
quikie22 wrote:
Sadly I stay far far away. I believe the postage will cost quite a bit. I am from a place called Malaysia. It is located just south of Thailand (Siam). I don't mind paying for the postage charges though I suspect the time taken to arrive might be unpredictable.

http://maps.google.com.my/maps?client=s ... CBgQ8gEwAA


No problem at all, please PM me your address.

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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Tue Nov 02, 2010 8:19 am 
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Now, here is the picture from the link that ErikdeBest posted on DIYAudio forum:

Image

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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Tue Nov 02, 2010 9:00 am 
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As you can see, with 350V cathode-anode and 100 mA idle current on 2k5 load I am getting up to 8W of output power. However, this regime results in significant amount of 2'nd order product of distortions that may be accessible since our perception tends to ignore low order distortions upon certain degree. Some audiophiles even prefer them because they create illusion of higher loudness.

If to use your 5K transformers distortions will be lower, and lower will be output maximal power.

GU-50 is rated for 40W anode dissipation, and anodes are made from nickel alloy that guarantees tubes are alive after dissipating more than 100W of power. So I am going to shift idle current even higher, using 470 Ohm cathode bias resistors.

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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Tue Nov 02, 2010 3:03 pm 
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Why do we want a higher bias current? To increase the power output? Higher linearity?


 
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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Tue Nov 02, 2010 6:57 pm 
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Joined: Tue Feb 10, 2004 12:30 pm
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Location: Pleasant Hill, California
quikie22 wrote:
Why do we want a higher bias current? To increase the power output? Higher linearity?


Both. Higher linearity on the same power, or higher power with the same linearity. Shift the load line a bit up and compare.
The tube is capable of dissipating more than 35W, so let's use it.

However, another limiting factor is an output transformer: it may saturate on higher current. Mine will be for 10W output.

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