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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Mon Nov 08, 2010 9:01 am 
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wavebourn wrote:
In terms of sound MOSFET has higher transconductance, tube has lower capacitances. Depending of power needed to drive you may decide what is more optimal.

I see.

Quote:
Take voltage on it's drain, it is provided by a voltage stabilizer, in respect to it's source that depends on first grid bias voltage you need.

Ok. Understood.


Quote:
You can't make system unstable reducing feedback. You can make it unstable increasing feedback: the criteria is gain 1+ and phase shift 180 degrees + starting from some frequency. I.e. accumulated phase shifts starting from some frequency turn negative feedback into positive one, so if gain on this frequency is above unity no doubt it starts oscillating.

Good. I understand about the phase shift causing it to become positive feedback instead of negative. Just wanted to confirm stability of totally removing the feedback loop.

Quote:
Fatiguing/unpleasant when people try to hide under feedback big errors that don't sound good. Try exactly such an amp with no feedback, you wan't listen to it at all.

I suspect that is the case. I went for all the wrong amps for the wrong reasons previously, Highest power, lowest THD, ...typically these were all poor design solid state class AB amps with lots of feedback to achieve those goals.... their sound made me depressed. I always ended up playing it very loud (as you say, to hide the poor sound) or totally turn it off.
Now i have seen the light Smile and begin to understand the meaning of good sound. Also appropriate power and listening levels. Smile


Quote:
Do you remember my explanation about blocking distortions?

Ooops... hehehe.. forgot about that. My little brain was only thinking about the drive characteristics.


 
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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Mon Nov 08, 2010 9:11 am 
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quikie22 wrote:
wavebourn wrote:

Do you remember my explanation about blocking distortions?

Ooops... hehehe.. forgot about that. My little brain was only thinking about the drive characteristics.


You can use as well transformer coupling between driver pentode and output triode grid. No CF is needed.

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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Mon Nov 08, 2010 9:31 am 
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wavebourn wrote:
You can use as well transformer coupling between driver pentode and output triode grid. No CF is needed.


An interstage transformer... 1:1 should be ok? How do I connect? Exactly as a OPT for primary? But the secondary with one end to the g1 and the other to ground? Interstage trans very expensive here... will try the CF first...


 
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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Mon Nov 08, 2010 9:48 am 
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Yes, it is possible to use 1:1 transformer for "left handed" triode, but for "right handed" one lower ratio would be more optimal. You may estimate voltage swing on driver anode, and on output grid, then calculate.

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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Mon Nov 08, 2010 3:36 pm 
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Here is the info from DIY Audio forum:

artosalo wrote:
The dc-grid current (=bias) for GU50 was around 12 mA and bias voltage about + 7 volts.
[/quote]

Here are curves I posted there from Telefunken 1941 datasheet:


Attachments:
LS50-3gridstogether.jpg
LS50-3gridstogether.jpg [ 158.53 KB | Viewed 17324 times ]

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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Mon Nov 08, 2010 3:51 pm 
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wavebourn wrote:
but for "right handed" one lower ratio would be more optimal

What do you mean by one lower ratio?? 1:0.5?


 
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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Mon Nov 08, 2010 4:08 pm 
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quikie22 wrote:
wavebourn wrote:
but for "right handed" one lower ratio would be more optimal

What do you mean by one lower ratio?? 1:0.5?


You can calculate it easily. I think something like 10:1

By the way, here is my version of right-handed triode output:


Attachments:
gubernator-5.jpg
gubernator-5.jpg [ 117.22 KB | Viewed 21863 times ]

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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Mon Nov 08, 2010 6:08 pm 
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Why the choice of the 12L6GT? I guess a 6P3S should work just as well there?
How do we get -75V for the 12L6 cathode?


 
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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Mon Nov 08, 2010 6:19 pm 
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quikie22 wrote:
Why the choice of the 12L6GT? I guess a 6P3S should work just as well there?

No. 12L6GT is more linear than 6L6 (6P3S), works on lower voltages (we need 20V peak to peak swing only), and what is significant, when self-biased for 50 mA on 150V has +7-8 volt on cathode, exactly as needed for right-handed GU-50.

Quote:
How do we get -75V for the 12L6 cathode?


The same way as before, from shunt regulator.

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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Tue Nov 09, 2010 1:29 am 
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I like it...


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gubernator-6.jpg
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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Tue Nov 09, 2010 6:06 am 
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cool... looks like an extremely simple and elegant design. very tempting to do this one now, but have to get a OT first (closest I can get is 8K or 16K). can you please explain the choice of tubes for this design? plate-plate FB (no more gyrator because of this). maybe I will build this first... hehehehe.. just that I don't have the tubes, any others can replacce in the meantime? I will try to get 12L6GT from ebay.


btw, the site did not have any more 6c14B-N, this is so sad Sad Crying or Very sad ... but I found the prices get good discounts. are there any other tube I should look at as well? I know 6J5P since it can be used for the right handed gu-50... also i don't quite fully understand russian, so do not know about the delivery terms and costs, not even sure if they send to Malaysia. ... will try to get my friend to translate for me.


 
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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Tue Nov 09, 2010 8:20 am 
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quikie22 wrote:
cool... looks like an extremely simple and elegant design. very tempting to do this one now, but have to get a OT first (closest I can get is 8K or 16K). can you please explain the choice of tubes for this design? plate-plate FB (no more gyrator because of this). maybe I will build this first... hehehehe.. just that I don't have the tubes, any others can replacce in the meantime? I will try to get 12L6GT from ebay.


btw, the site did not have any more 6c14B-N, this is so sad Sad Crying or Very sad ... but I found the prices get good discounts. are there any other tube I should look at as well? I know 6J5P since it can be used for the right handed gu-50... also i don't quite fully understand russian, so do not know about the delivery terms and costs, not even sure if they send to Malaysia. ... will try to get my friend to translate for me.


You may use Google translate.

Also, they have English version of site.

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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Tue Nov 09, 2010 9:26 am 
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12CU5 would fit instead of 12L6GT

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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Sat Nov 20, 2010 12:57 pm 
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wavebourn wrote:
12CU5 would fit instead of 12L6GT


Also, 6П1П can be used, with 30 mA idle current. That means 83/30= 2K7 cathode load resistor.

Image

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 Post subject: Re: GU-50 Single Ended Amplifier Design
PostPosted: Tue Nov 23, 2010 8:18 am 
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ok. Will try to get either of the tubes.... this will be a future project Smile , once I am better at the simpler circuits...

By the way, was listening to your performances recordings, what was the AMP used? the Pyramids? Tower? or the others Barracuda, Alligator etc? The sound seems so powerful and dynamic yet maintain the sweetness of tubes... very impressive.


 
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