71A Direct Heat Triode Single End Class A Amplifier

Musik007 · 11th April 2010, 06:32 PM

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

We started to make our first 71A amplifier.

Musik007 · 12th April 2010, 06:05 PM

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

Musik007 · 13th April 2010, 05:05 PM

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

This is maple wood chassis.

Musik007 · 18th April 2010, 05:07 PM

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

Musik007 · 18th April 2010, 05:49 PM

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

Musik007 · 03:17 PM

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

Musik007 · 03:41 PM

71A amplifier is Twin Audio Sinfonia series tube amplifer.

Musik007 · 20th April 2010, 05:26 PM

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

Musik007 · 21st April 2010, 05:18 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, 09:23 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.

11th April 2010, 06:32 PM	#1
Musik007 diyAudio Member Join Date: Nov 2009	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://www.mif.pg.gda.pl/homepages/f.../029/7/71A.pdf We started to make our first 71A amplifier.

19th April 2010, 06:06 PM	#6
Musik007 diyAudio Member Join Date: Nov 2009	This very rare and expensive vintage ballon shaped UX-71A triode (171A, 271A, 371A) delivers sweet, soft and smooth sound. Last edited by Musik007; 21st July 2010 at 03:17 PM.

20th April 2010, 04:08 PM	#7
Musik007 diyAudio Member Join Date: Nov 2009	71A amplifier is Twin Audio Sinfonia series tube amplifer. Last edited by Musik007; 6th May 2010 at 03:41 PM.

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12th April 2010, 06:05 PM	#2
Musik007 diyAudio Member Join Date: Nov 2009	In the first, drill holes for tube sockets, transformers and knobs on top plate. The layout of 71A amplifier was complete.

13th April 2010, 05:05 PM	#3
Musik007 diyAudio Member Join Date: Nov 2009	The circuit is 6SL7-71A single end class A with 5Y3 rectifier. This is maple wood chassis.

18th April 2010, 05:07 PM	#4
Musik007 diyAudio Member Join Date: Nov 2009	71A amplifier is complete. 6SL7-71A single end with 5Y3 recitifer.

18th April 2010, 05:49 PM	#5
Musik007 diyAudio Member Join Date: Nov 2009	RCA 6SN7GT, RCA UX-71A and Mazda 5Y3GB.

20th April 2010, 05:26 PM	#8
Musik007 diyAudio Member Join Date: Nov 2009	The price of this 71A single end amplifier is USD900.

21st April 2010, 05:18 PM	#9
Musik007 diyAudio Member Join Date: Nov 2009	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.

22nd April 2010, 09:23 AM	#10
Musik007 diyAudio Member Join Date: Nov 2009	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.

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