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 Post subject: Gubernator - 71 single ended amplifier
PostPosted: Sun Jan 07, 2018 1:54 am 
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Шаман, типа...

Joined: Tue Feb 10, 2004 12:30 pm
Posts: 7302
Location: Pleasant Hill, California
Well;

it was the time to make some SE amp finally, to test my theory that SE has minimum of possible audio distortions on decaying sound, hence sounds more "airy". However, there is another problem wit them; usually as soon as they sound nice on low volume, people tend to build them with triodes. Pretty low output power forces to use them on higher volume that would drive them out of headroom on peaks. Since vacuum triodes without additional feedback cause pretty soft clipping without nasty sounding distortions, it is the usual way to build them: 2 or 3 triode stages depending on tubes, no or little feedback. As the result, they have reputation of amps good for audiophile recordings with one solo and few instruments, but not good for orchestra and other music that does not tolerate pretty high intermodulation distortions caused by relatively high low order errors of triodes with no feedback.

One more thing that adds to negative reputation of such amplifiers, it pretty high output impedance. A first, it causes sloppy bass, since can't damp modern speakers, and requires enormously expensive output transformers to reproduce the whole range of audio frequencies.

Can it be done differently, first of all, to preserve "airy" sound of SE amplifier, but without drawbacks, like high intermodulation distortions of loud sounds and weak speaker control?

Yes!

So, I after extensive research, I selected tubes. GK-71 for the output stage, and 12HL7 as a driver.

GK-71 is a quite powerful directly heated pentode, with graphite anode, that can dissipate 135W according to datasheet. It was manufactured for Soviet military transmitters, used in critical application, and is quite reliable. Here is the picture attached that shows how linear it is!


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gk71gr.gif
gk71gr.gif [ 19.24 KB | Viewed 43 times ]

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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: Gubernator - 71 single ended amplifier
PostPosted: Mon Jan 08, 2018 2:28 pm 
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Шаман, типа...

Joined: Tue Feb 10, 2004 12:30 pm
Posts: 7302
Location: Pleasant Hill, California
For the driver I selected 12HL7 tube. It was designed for video amplifiers, so is very linear, and has high Gm.

21 mA/V versus 15 of 6P15P.

As the result, only 2 stages were needed for 45W output driven by 0.7V input.


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Screenshot from 2018-01-08 13-26-39.png
Screenshot from 2018-01-08 13-26-39.png [ 318.38 KB | Viewed 28 times ]

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