AudioCircle

Audio/Video Gear and Systems => Low Wattage Systems => Topic started by: lego4040 on 19 Mar 2018, 03:23 am

Title: Schematic for single ended 71A stereo amp
Post by: lego4040 on 19 Mar 2018, 03:23 am
So I'm trying to set some builds so I can fill up my bench and I'd like to try a 71A. As simple as it can get is preferable, since I strongly believe in the K.I.S.S. When I google a SE 71A schematic 2A3/45 comes up a lot, I am no electrical engineer but I do have tube amp builds under my belt . I'll read and study a build for 6 months sometimes before I build so I know whats ahead of me and to get to know the circuit. Thank you and much appreciated
Title: Re: Schematic for single ended 71A stereo amp
Post by: FullRangeMan on 19 Mar 2018, 03:42 am
The schematics I copy from internet were incomplete or purposely wrong.
Title: Re: Schematic for single ended 71A stereo amp
Post by: doggie on 21 Dec 2019, 01:20 pm
The 71A is my favorite tube with the 45 following just behind. Needs some very efficient speakers though. I made this as a headphone amp years ago. No schematic. Scratch built with a lot of experimentation. I used WE 417a tubes on the input.

I sold it and wish that I could buy it back.

(https://www.audiocircle.com/image.php?id=202298)
Title: Re: Schematic for single ended 71A stereo amp
Post by: FullRangeMan on 21 Dec 2019, 09:54 pm
Great amp, congratulations.
How is the 417A sound?
The OPTs are Tango?
Title: Re: Schematic for single ended 71A stereo amp
Post by: doggie on 22 Dec 2019, 12:45 am
Yes. Tangos.

I really liked the combination of the 417a and the globe 371A tubes. I had a pair of Lundahl interstage transformers underneath. I tried them as ITs but ended up wiring them to choke load the drivers. I played with DC and AC filaments also. AC sounded the best to me but had hum. I ended up using DC filaments with small chokes in the filtration.

I thought that it sounded great but moved on to try other things for my headphone listening. Wish I still had it.
Title: Re: Schematic for single ended 71A stereo amp
Post by: FullRangeMan on 22 Dec 2019, 12:53 am
Maybe the hum came from the 417 small space between filament and cathode, so DC are recommended, but sino amps usually use a hum pot for lower costs and fewer parts.