Aikido 2a3 and JE 300B

[SDS-PAGE]

I am thinking about for my next project I would p2p wire a DHT SET. I came across Aikido 2a3 and JE 300B that look pretty easy to build. Has anyone had any experience with either one of these amps? What's your impression? Also, how much is minimal hum or noise in these amps? I notice that there is a hum balance in the cathode of output tubes. Is it possible to completely get rid of hum/noise with this way? Or, will I need to rectify like in GSG? Thanks!

[EWBrown]

I've found that with 2A3s, and an AC hum balance pot (usually 50 ohms, WW, or use 2 20-22 ohm 2W resistors and a 10 ohm WW pot in the middle) will get the 60Hz hum out. As the filament voltage rises, this approach can be somewhat less effective, and for 300Bs, 6B4Gs, 6A3s, etc DC is better, overall.

Though there some traditionalists who claim that the audio quality diminishes with DC filament power, I never found it to be so, as far as I could tell. Then my ears are merely copper, not golden Yellow_Light_Colorz_PDT_08 Yellow_Light_Colorz_PDT_09

The older circuits with DHTs simply used center tapped 2.5, 5 or 6.3VAC filament trannies, the cathode resistor connected to the CT, and no hum balance pot was used. This works if the trannie is well-balanced and the tube filament has evenly distributed resistance along its total length.

The balance pot works for 60 Hz (or 50 Hz for overseas) AC only, the 120Hz (or 100 Hz) PSU ripple is a whole different situation.

Any of the JE Labs circuits are fine, though in one of Jose's "Simple 2A3" circuits he used a shared cathode resistor and filament trannie for both 2A3s, that works, but the tubes have to be well matched, and this reduces channel separation (and imaging) somewhat. I haven't trried the "Aikido" 300B approach, it looks like it should work well, and John Broskie really knows his stuff, so I see no problem other than increased circuit complexity.

FWIW, Jeff Larson's Aikido 2A3 link is here:

http://home.att.net/~abraxasaudio/proje ... 2a3-2.html

HTH

/ed B in NH

[SDS-PAGE]

I am leaning towards building a pair of JE 300B monoblocks (schematics found on Angela website). I see that the amp uses Angela universal PT (380-320-0-320-380 at 200 mA). Could I substitute Hammond 274BX (375-0-375 at 175 mA) for it? If not what other Hammond PTs could I use? This is going to be one costly project. I will probably need to put in about a grand.

[ecir38]

SDS, check out this amp I am thinking of building. Cost should be close to the JE. I put together an updated BOM if anyone is interested.

http://www.pmillett.com/elinear.htm

[SDS-PAGE]

Very well documented. Those KT-88s should give you a plenty of wattage.

[77seriesIII]

SDS-Page

Care to pony up the link to the 300b schematic? I am having ID 10 T issues and when I search for angela I keep getting naked pictures. Of course it takes me awhile, for some reason, to remember what I was looking for. Now the sad part I remember what I was looking for and start the process all over again.

/e

Never mind found it...pricey build

One thing in re-reading the post the stuff on angela and on http://www.iol.ie/~waltonaudio/mk1construct2.html, I think you may be able to use trafomatic iron. They build to spec and their iron is not expensive. I think the ones for the GSG board were $84 and they are toroidal.

http://audio.engineeringvista.com/ Just put in a quote with Boris and he will get back to you within a day or so.

/e

[SDS-PAGE]

Thanks for the info. on Trafomatic irons. Are you sure they make SE toroidal OPTs? Their website says toroidal OPTs for PP amps only.

[77seriesIII]

I want to say we did a group order on those. But the best thing to do is ask.

So I guess the honest answer is I'm not sure but ask.

/e

[EWBrown]

I've seen small (5W, 5K primary) E-I type SE OPTs from Trafomatic, but no toroidal SE OPTs. Toroids and air-gaps don't easily co-exist...

Closest thing would be to use two "C" cores, with an air gap between them.

/ed B in NH

[77seriesIII]

Ahh damnit...its that reading thing again. TOROIDAL OPTs...freakin idiot. Yep I think everyone is right but not me. We did order OPTs but they were not Toroidals. Sorry for the confusion.

[EWBrown]

A short while ago I bought a set of the octal dual-mono Aikido boards, and I'm considering setting them up as SET drivers, 6SL7 input and 6SN7 or 6BL7 output section. Max overall gain would be around 35 (half of 6SL7's mu and a few percent lost in the CF stage).

The 9 pin version might be better for this application, as it can use a 12AX7 or 12BZ7 as the "input" tube and thusly achieve an overall gain around 50, which would bode better for 2A3s and 300Bs. .

I've built an octal stereo Aikido linestage board kit (all 6SN7s) and one of their somewhat unconventional step attenuators, just never finished integrating it all into a finished unit, yet.

/ed B in NH