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-   -   71A Direct Heat Triode Single End Class A Amplifier (http://www.diyaudio.com/forums/twin-audio/164912-71a-direct-heat-triode-single-end-class-amplifier.html)

Musik007 11th April 2010 05:32 PM

71A Direct Heat Triode Single End Class A Amplifier
 
71A is a vintage direct heat triode power tube for audio amplifier. 71A is firstly made by Cunningham as CX-371A in USA in 1930s. Although 71A is a low plate voltage (180V max.) and low ouput power (0.8W in SE class A) triode, it can drive loudspeakers in high sensitivity. Nowadays, more and more audiophiles like the sound of vintage 71A.

http://i30.photobucket.com/albums/c312/organ/71A.jpg

http://www.mif.pg.gda.pl/homepages/f.../029/7/71A.pdf


We started to make our first 71A amplifier.
http://i30.photobucket.com/albums/c3...an/71ASE-3.jpg

Musik007 12th April 2010 05:05 PM

In the first, drill holes for tube sockets, transformers and knobs on top plate. The layout of 71A amplifier was complete.

http://i30.photobucket.com/albums/c3...an/71ASE-4.jpg

Musik007 13th April 2010 04:05 PM

The circuit is 6SL7-71A single end class A with 5Y3 rectifier.

http://i30.photobucket.com/albums/c3...an/71ASE-1.jpg

This is maple wood chassis.
http://i30.photobucket.com/albums/c3...an/71ASE-2.jpg

Musik007 18th April 2010 04:07 PM

71A amplifier is complete. 6SL7-71A single end with 5Y3 recitifer.

http://i30.photobucket.com/albums/c312/organ/71A-01.jpg

http://i30.photobucket.com/albums/c312/organ/71A-02.jpg

Musik007 18th April 2010 04:49 PM

RCA 6SN7GT, RCA UX-71A and Mazda 5Y3GB.

http://i30.photobucket.com/albums/c312/organ/71A-03.jpg

http://i30.photobucket.com/albums/c312/organ/71A-04.jpg

Musik007 19th April 2010 05:06 PM

This very rare and expensive vintage ballon shaped UX-71A triode (171A, 271A, 371A) delivers sweet, soft and smooth sound.

http://i30.photobucket.com/albums/c312/organ/71A-07.jpg

http://i30.photobucket.com/albums/c312/organ/71A-09.jpg

http://i30.photobucket.com/albums/c312/organ/71A-13.jpg

Musik007 20th April 2010 03:08 PM

71A amplifier is Twin Audio Sinfonia series tube amplifer.

http://i30.photobucket.com/albums/c312/organ/71A-05.jpg

Musik007 20th April 2010 04:26 PM

The price of this 71A single end amplifier is USD900.

Musik007 21st April 2010 04:18 PM

We adjusted 71A under AC filament supply and would be a little bit hum, but maintain the sound of 71A warm and smooth.
The plate current of 71A is 20mA.

Musik007 22nd April 2010 08:23 AM

This is the output transformers for 71A single end. The primary impedance is 5K and secondary impedance is 8 ohms and 16 ohms. The output power is 7W. The steel core used is Z11. The transformers were made in Poshan, Hong Kong.

http://i30.photobucket.com/albums/c312/organ/CD049.jpg

http://i30.photobucket.com/albums/c312/organ/CD052.jpg


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