71A power amp

johnsonad · 3513

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Offline johnsonad

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on: January 01, 2014, 01:25:58 PM
I'm in need of a new project and would like to try a 71A based power amp. I've found a couple of schematics floating around the web and was wondering if any of the current or passed BH designs would work well with this tube?  Maybe a modded SEX? Possibly a shunt regulated design? How about an all DHT design with the 3S4 as a driver and battery filaments all around?  I'm open to ideas and suggestions :)

Aaron Johnson

Offline galyons

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Reply #1 on: January 01, 2014, 01:44:05 PM
Are you thinking a single 71A per channel or PSE?  I looked at doing a 2 per channel PSE using a Golden Tube Audio SE40, (3 6L6GC per channel), chassis and iron. (The board suffered thermal evaporation!  >:( )  The PT, choke and 1.9K OPT's are really quite nice iron.  I moved to 2A3's simply because they could better handle the higher DC of the PT.

Cheers,
Geary

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Offline johnsonad

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Reply #2 on: January 01, 2014, 01:53:41 PM
Single tubed output. 700mW is enough for my speakers and my usual listening level. I'll probably use it for 80 Hz and up.

Aaron Johnson

Online Paul Joppa

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Reply #3 on: January 01, 2014, 04:38:07 PM
The only thing that comes close for power supply is Mainline. Has a regulated filament supply that could easily be adapted to 5.0vDC, and the shunt regulated 225v is perfect for the 71A at 180v plus 40v bias. It would have to be monoblocks, but a lot of re-useable parts. Quite a design extrapolation!

To avoid adding new power supplies, I'd use an indirectly heated driver and shunt reg tube. Heck, maybe even use the 6C45 as a driver!

Paul Joppa

Offline xcortes

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Reply #4 on: January 02, 2014, 03:54:06 AM
I'm in for this one :)

Xavier Cortes

Offline johnsonad

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Reply #5 on: January 02, 2014, 03:59:29 AM
Wow Paul, what a conversion! I'll have to think about it at that price.
« Last Edit: January 02, 2014, 04:02:55 AM by johnsonad »

Aaron Johnson

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