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List of 2A3 SE Circuit Designs?

goldleaf

goldleaf

Super Member
Anybody seen a list of 2A3 single ended designs out there? Looking for comparisons and pros and cons - in particular, curious about the newer, current production amps vs vintage amps.

This is what I have so far:
1. Tango http://www.single-ended.com/2A3/2A3single.htm
2. Shishido http://lagarto-ex-infoseek.jp/shishido/shishido-skema.htm
3. Cairo http://www.single-ended.com/kairo1.htm
4. Loftin-White http://diyaudioprojects.com/Schematics/2A3-Loftin-White-Tube-Amplifier-Schematic.htm

Also, this thread describing some designs:
http://www.audiokarma.org/forums/showthread.php?t=271007
 
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Funny you mention that one. I just got my first SET amp from fellow AK'er roberts67. It is the Get*Set*Go SET 6B4G tube amp. Looking forward to testing it with my new Frazier Mark V's from fellow AK-er in RTP Roger (I think they used to belong to AKer Analog Addict).

So things are under way. Getting the hankering to build some things, hence checking these designs for SET's. Also planning to build Poultrygeist's open baffle speaker design based on the quarter-wave ob over h frame sub idea.

Slowly getting feet wet so one day I can build a monster like that GM 70 Dennis is building :D

or this monster http://lampizator.eu/AMPLIFIERS/GM-70/GM70amplifier_mono.html

Gotta learn to crawl, walk, before I can run... :music:
 
That thread you mentioned is one I started quite awhile ago, looking for a 2A3 design myself. I think I'm finally going to build one with my buddy Dennis across town. If you are interested in SE designs, you really should go over and meet Dennis one day and listen to some of his stuff. It'll knock yer socks off....:thmbsp:
 
analog addict said:
That thread you mentioned is one I started quite awhile ago, looking for a 2A3 design myself. I think I'm finally going to build one with my buddy Dennis across town. If you are interested in SE designs, you really should go over and meet Dennis one day and listen to some of his stuff. It'll knock yer socks off....:thmbsp:
Click to expand...

Definitely looking forward to meeting you all. Roger mentioned you all's amazing setups!

If you like cigars, I've got some that will knock your socks off. :thmbsp:
 
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I should poke around for some vintage designs I have encoutered. I am tempted to bring my 2A3 monoblock from storage and maybe make something of it rather than dust collector.
 
goldleaf said:
Definitely looking forward to meeting you all. Roger mentioned you all's amazing setups!

If you like cigars, I've got some that will knock your socks off. :thmbsp:
Click to expand...

Cigars? Nah, I just keep a 300 cigar humidor lying around cause it's a nice looking piece of furniture....:smoke:
 
Trio said:
I should poke around for some vintage designs I have encoutered. I am tempted to bring my 2A3 monoblock from storage and maybe make something of it rather than dust collector.
Click to expand...

Pictures?

I am extremely curious about people's output transformer selections. Have a hunch the secret/road to success passes through "there".

Wish I could read Japanese so I could follow the 60+ years of Audiomaniac writing.
 
I'll throw my own 2A3 amp into the mix. This is based on Jack Eliano's DRD amp also known as the 'Monkey'. IMO the key to great sound with a 2A3 is to direct couple the driver to the 2A3. I wouldn't consider any design that RC coupled the driver to the OP tube.

So what's so special about the DRD/Monkey? First of course is the direct coupling, so beyond that you only have 3 caps in the entire amp and good caps are expensive. Excellent coupling caps are very expensive for the best and this amp doesn't have any.

The 6N23P is a super tube: quiet, powerful and great sounding. The 6N23P drives the 2A3 from 1 volt input so no preamp is required and MOST IMPORTANT a preamp will degrade the sound. So now you have an amp with only two stages and no coupling caps. There is not a lot there to muck up the sound. This beast is TRANSPARENT!

Another point: this amp is designed around the JJ 2A3-40 which is another super tube. It is relatively inexpensive and has great sound but most important it can withstand considerably more plate dissipation than the original 2A3: notice the operating point is 290V @ 65mA. You can run a 2A3 at those operating points, but not for long...

I have built this amp with all Magnequest iron and with all Electra-Print iron, but unfortunately neither winder is making power transformers any longer; but Edcor and Hammond make suitable transformers. For the output there are many options, but I like the 3k ohm Electra-Print. Note that 2.5k is the traditional IP impedance used with the 2A3, but I use 3k in my amps. Draw up some plate curves and you will see that there is only a slight difference with the 3k offering a fraction less power and a fraction less distortion.

The 100H plate choke is Electra-Print; the ten ohm resistor is to measure the plate current through the driver to help select the 6N23P. I bought a dozen 6N23Ps off of epay for a few $ each and select those that bias about 120V on the plate @ about 12mA with the diode as bias. Over half were within spec. You can't beat the 5V3A/5AU4 as a rectifier. It is better sounding and more rugged than the GZ34 and costs about $10 on epay.

The 2A3 cathode resistor stack is a little fiddly and the most difficult part of the build. Use some variable power resistors to dial it all in as your power transformer will be different. Select the operating point of the 2A3 and use Ohm's law to determine the resistor values.
 

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goldleaf said:
Any links?

Saw some odd things in the research. Still a newbie, so if you are not pulling my leg, is there a website?

http://www.diyaudio.com/forums/tubes-valves/183782-what-i-need-safe-use-mercury-rectifier.html

The diyaudio site is awesome but the level of many of the people there is way over my head at the moment. Still in the stage of finding Yoda to guide the way to the force. :lazer:
Click to expand...

I might have a scrawled schematic somewhere. Micah thought up the Mosfet part. It can also be run as direct coupled, the mosfet gives it a bit more power. I'll look around some, it should be in a file folder.
 
Mine will most likely be a 6CL6 - 2A3 combo as Bricktop and I originally envisioned it. I have a dozen old stock 2A3s that I'm planning on rolling, with some Sovteks for testing.
 
analog addict said:
Mine will most likely be a 6CL6 - 2A3 combo as Bricktop and I originally envisioned it. I have a dozen old stock 2A3s that I'm planning on rolling, with some Sovteks for testing.
Click to expand...

So is that an original design then? Very curious to see what your schematic looks like once it's built out. What is the advantage of using a 6CL6? What transformers will you be using? The Transcendar's; are they better that Edcor or one of the other current production units in terms of the core materials?

Did you ever end up finding out much about the Mikkel Simonsen design? http://www.stiftsbogtrykkeriet.dk/~mcs/2A3/index.html

Checking out the Bottlehead Stereomour design, I found a claim that the paramour design is also based on the Parafeed circuit of Mikael Abdellah's (2003)
(http://www.diytube.com/phpBB2/viewtopic.php?t=1960)
but according to Bottlehead,
(http://www.bottlehead.com/store.php?crn=44&rn=447&action=show_detail)
it's a Paul Joppa original design from 2000. Can anyone clarify this?

The Abdellah Parafeed is a KT88 based design.
F01-KT88-Amplifier.png


Has anyone seen such a schematic for the 2A3? I've only found these references
http://www.diyaudio.com/forums/tubes-valves/118428-any-advice-modifying-2a3-set-amp-parafeed.html
http://www.diy-audio-guide.com/parafeed-2a3.html
 
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You've prolly already seen it...

But here's the working draft....

2A3designroughdraft_rev1-1.jpg


I'm guessing there will some modifications as this project gets up to speed....:scratch2:

As far as the 6CL6 goes, the best I can tell you is it will be triode strapped, and that it was chosen for it's operating characteristics and that fact that they are cheap and there are a lot of them rolling around.

The OPTs will prolly be swapped back and forth and consist of a pair of 3K Transendars with a 40% UL tap, a pair of UTC LS-63s, which are normally a PP transformer, but according to the data sheet, can be set up for SE 2A3 (we'll see) and a pair of Dennis' super secret custom built OPTs with a special feedback winding. Should be quite interesting. I actually owe him a phone call to see where he's at with ordering the parts....:scratch2:
 
Palustris said:
I
I have built this amp with all Magnequest iron and with all Electra-Print iron, but unfortunately neither winder is making power transformers any longer; but Edcor and Hammond make suitable transformers. For the output there are many options, but I like the 3k ohm Electra-Print. Note that 2.5k is the traditional IP impedance used with the 2A3, but I use 3k in my amps. Draw up some plate curves and you will see that there is only a slight difference with the 3k offering a fraction less power and a fraction less distortion.
Click to expand...

Very nice Palustris!

Been wondering how people come to choose their iron. How do you pick between Magnequest, Audio Note, Tango and other premium brands vs. the less expensive offerings from Edcor and the like? Is it down to core material and 3k or can you hear the SQ effects from taking other factors into account?

I have not come across any articles that convincingly argue how designers pick and whether there are audible, sound quality reason for a particular trans iron.
 
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