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211 SE power amp
http://diyaudioprojects.com/Forum/viewtopic.php?f=9&t=4514
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Author:  mwhouston [ 04 Oct 2013, 18:20 ]
Post subject:  Re: 211 SE power amp

Suncalc wrote:
Sorry for the delay. I'll get the whole thing posted tonight (on my side of the world ;) ).

Currently I'm thinking Edcor CXSE25-8-10k. The operating point is only at 59mA so current and core saturation is no problem. I'm not worried about the voltage because the dielectric breakdown on the wire that Edcor uses is well above 3000v. Even if their HiPot standard is not that high I think the outputs will be fine.

More later.

Matt: no hurry, I have a few minor projects to start and complete first. That is why I started this thread early so the pressure is off for the design. I just thought it would be nice to generate discussion etc. early in the piece.

Author:  Geek [ 05 Oct 2013, 06:52 ]
Post subject:  Re: 211 SE power amp

mwhouston wrote:
Do you know what the idle current rating is? Is it new or used?


Were you talking to me? :confused:

If so, EM0774 Imax-idle is 90mA and new, since you'd have to get it from them (I don't stock them).

Cheers!

Author:  mwhouston [ 05 Oct 2013, 09:40 ]
Post subject:  Re: 211 SE power amp

Geek wrote:
mwhouston wrote:
Do you know what the idle current rating is? Is it new or used?


Were you talking to me? :confused:

If so, EM0774 Imax-idle is 90mA and new, since you'd have to get it from them (I don't stock them).

Cheers!

I thought you had some to sell. My bad.

Author:  Geek [ 05 Oct 2013, 17:35 ]
Post subject:  Re: 211 SE power amp

Heh, a USPS box from Carlsbad, NM would be a fraction of the cost as a Canada Post one (Down Under the **THE** most expensive country to ship to from Canada). If I sold them, they would have been stupid expensive to ship :(

Author:  mwhouston [ 05 Oct 2013, 18:30 ]
Post subject:  Re: 211 SE power amp

Geek wrote:
Heh, a USPS box from Carlsbad, NM would be a fraction of the cost as a Canada Post one (Down Under the **THE** most expensive country to ship to from Canada). If I sold them, they would have been stupid expensive to ship :(

Shipping generally doubles my purchase cost.

Author:  Geek [ 05 Oct 2013, 23:06 ]
Post subject:  Re: 211 SE power amp

<rant>
Other than the USA, Australia was my biggest export country until the new rates. They killed a LOT of our small business exports in one swoop :bawling: :mad:
</rant>

Author:  Suncalc [ 06 Oct 2013, 13:34 ]
Post subject:  Re: 211 SE power amp

Well, better late than never. I have an amp design to present, although I will include power supply and filament supply designs in a later post. First the particulars:

Power into output transformer: 20.0W/channel (≈18W @ the speaker)
Full power distortion: 5.9% (almost exclusively 2nd harmonic)
Incremental distortion: 0.29%/watt
Low frequency rolloff: 5.6Hz
High frequency rolloff: 25.2kHz
bias recovery (τr): 32ms (worst case)
Input sensitivity for full output: ≈1.6 Vac

A couple of important points:

WARNING: This amplifier involves VERY high supply and operating voltages. Voltages at this level are IMMEDIATELY LETHAL! This is true even when there is no apparent current return path! Appropriate build techniques should be maintained at all times. Materials such as wire and shielding should be rated for this voltage level. Three wire grounded power connection is essential and ALL non-signal grounds must be directly tied to the chassis ground with a bonding resistance of not greater than 2mΩ. Service should NEVER be attempted with the amplifier power applied. Always ensure that power supply capacitors have adequate time to discharge before attempting servicing. Voltages must be measured with fixed instrumentation only. Never attempt to probe a circuit with operating voltages at this level.

In addition: this design is right up against the CCS limits for the 211 tube. There should be margin in ICAS service, but at no time should the plate voltage exceed the 1259V figure. Adjustment should be provided for in the power supply to ensure this operation. Also note that the power tubes are dissipating almost 100W each in pure heat. They should be positioned is such a manner at to ensure adequate convection cooling. Hot air rising off the tubes will draw in cooler air around the base. A minimum clear area around each tube of about 4" radius minimum to ensure adequate convection cooling should be maintained. The two output tubes also should not be closer than about 5" to each other (envelope to envelope).

For those not really interested in the design details, I'll put the schematic first:
Attachment:
Amp Schematic (small).jpg

Now for those of you who are interested, here are the load lines for the power and driver stages:
Attachment:
Load Line - Power Stage.jpg
Attachment:
Load Line - Driver Stage.jpg

As always, questions and comments are more than welcome. Please let me know what you think.

Author:  Geek [ 06 Oct 2013, 15:45 ]
Post subject:  Re: 211 SE power amp

Awesome research!

Now I want to try one.... I find 845's a tad "dry" ;)

Author:  mwhouston [ 06 Oct 2013, 18:14 ]
Post subject:  Re: 211 SE power amp

Geek wrote:
Awesome research!

Now I want to try one.... I find 845's a tad "dry" ;)

Firstly thanks Matt for all your hard work so far. I know you're a busy man so thanks for taking the time to be so detailed.

Geek: do you think the 211 may be a better sounding tube? Most amps I see with this type of tube do use 845s.

Author:  Geek [ 06 Oct 2013, 20:55 ]
Post subject:  Re: 211 SE power amp

Better? *philosophical cap on* Well, NO tube is better than the other, just different..... *philosophical cap off*

I have not heard one. You tell me! :D

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