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Old 8th September 2013, 09:28 AM   #361
hpeter is offline hpeter  Europe
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Quote:
Originally Posted by Magz View Post
Speaking of "Monster Amps with Massive Transformers"...
"no replacement for displacement""

but when fuse blows, any glass types become grenades more or less ?
Best what i could find were ceramic fuses 3,35" SIBA 185000
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Old 13th September 2013, 02:00 PM   #362
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The machining of the chassis is done.

All chassis parts save the faceplates have been sent off to Landfall Systems to be anodized smooth black (non-brushed finish). I had originally intended to have the top plate chromed to match my preamp but in thinking about it there is going to be so much light given off by the 883s that the last thing I need is a big reflector under them, so black they will be. That ought to help with heat dissipation from the top plate, as well.

Once the anodized parts come back, final assembly can begin!
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Old 17th September 2013, 06:49 AM   #363
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Originally Posted by Magz View Post
Once the amp goes into A2, however, the distortion spectrum changes, with much less 2H and more 3H. The second picture is the spectrum at 84W output into 4 ohms. Distortion is now predominantly 3H, with the 3H at .76%. This is what was seen in all analyses I ran with the amp in A2.
A2 distortion and it's spectra are extremely dependant on the driver. The lower it's output impedance the better. Most A2 amps are transformer coupled, but I've had better results using a very high gm cathode follower directly driving the power tube.

Quote:
Anecdotally, I've read reports that A2 sounds a little edgier and a little brighter than A1, and those FFT results seem to reinforce that. In any case, most listening will be in A1, except for crescendos and perhaps drunken volume cranking...
I've found that my A2 amps almost never actually transition to A2 unless I am playing it ridiculously loud, or into an inefficient speaker.


Quote:
Note: in order to get consistent, believable results from this LTSpice analysis, I had to disable all compression, force double precision math, and set max timestep to 1uS. Otherwise, there's a lot of hash and false peaks along the baseline.
Where is the force double precision option? I looked and was unable to find it...

Quote:
Originally Posted by tomchr View Post
Beware that the simulation is only as good as the models. If your tube model accurately models the tube characteristics and grid current in A2 mode, then you probably get good results. Personally, I've never been able to get accurate prediction of the THD of a tube circuit in LTspice. Especially when the circuit behavior near clipping (or A2) is simulated.

For DC and small-signal AC sims, I generally get a very good match between sims and reality.

~Tom
What we need is to get some talented folks together and hack some native, full fledged modelling code into an open source simulator like ngspice. Something like a vacuum tube version of the BSIM or Ebers-Moll models for semiconductors. It would be a daunting undertaking, but the results would be worth it.

Last edited by Defiant; 17th September 2013 at 06:52 AM.
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Old 17th September 2013, 12:50 PM   #364
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Quote:
I've found that my A2 amps almost never actually transition to A2 unless
I built an 845SE that makes 40 WPC in A2. It stays in A1 until 25 watts. A2 is only seen on peaks.....the same peaks where the speaker cone is nearing Xmax. You won't hear the amp's distortion, which on my design is still mostly 2H.

LT spice is good, but vacuum tube models where grid current is involved are usually not so accurate.
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Old 17th September 2013, 12:55 PM   #365
Magz is offline Magz  United States
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Originally Posted by Defiant View Post
Where is the force double precision option? I looked and was unable to find it...
.OPTIONS numdgt=7. Any number more than 6 will force LTSPICE to switch to double precision math on dependent variables.



In fact, here's a little webpage I ran across that talks about doing distortion predictions with LTSpice. Some nice little tidbits in there - notice how when he uses the default settings even his pure voltage source looks like crap!

Distortion measurements with LTSPICE | Audio PerfectionAudio Perfection

.
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Old 18th September 2013, 12:15 PM   #366
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Originally Posted by tubelab.com View Post
I built an 845SE that makes 40 WPC in A2. It stays in A1 until 25 watts. A2 is only seen on peaks.....the same peaks where the speaker cone is nearing Xmax. You won't hear the amp's distortion, which on my design is still mostly 2H.

LT spice is good, but vacuum tube models where grid current is involved are usually not so accurate.
The reason I suggested ngspice is that it is open source. Vacuum tube modelling could be coded directly into the simulation engine, which would allow control of parameters that are very difficult to do (accurately) with the current method of modelling.

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Originally Posted by Magz View Post
.OPTIONS numdgt=7. Any number more than 6 will force LTSPICE to switch to double precision math on dependent variables.



In fact, here's a little webpage I ran across that talks about doing distortion predictions with LTSpice. Some nice little tidbits in there - notice how when he uses the default settings even his pure voltage source looks like crap!

Distortion measurements with LTSPICE | Audio PerfectionAudio Perfection

.
Cool, thanks for the info!
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Old 18th September 2013, 07:43 PM   #367
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Hi Magz,

have You seen this one? It's from ESKA Germany
http://www.produktinfo.conrad.com/da..._3KV_500MA.pdf

It is for 3kV an 6kV...I 'm using the 3kV version.

best regards, Matthias
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Old 18th September 2013, 08:00 PM   #368
Magz is offline Magz  United States
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Originally Posted by Mister Ed View Post
Hi Magz,

have You seen this one? It's from ESKA Germany
http://www.produktinfo.conrad.com/da..._3KV_500MA.pdf

It is for 3kV an 6kV...I 'm using the 3kV version.

best regards, Matthias
Looks like another option for HV fuses. Thanks.
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Old 20th September 2013, 11:48 AM   #369
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Quote:
Originally Posted by Mister Ed View Post
Hi Magz,

have You seen this one? It's from ESKA Germany
http://www.produktinfo.conrad.com/da..._3KV_500MA.pdf

It is for 3kV an 6kV...I 'm using the 3kV version.

best regards, Matthias
Hi Matthias,

Nice tip, thank you!

Do you have a source for a suitable fuse holder, how do you handle this?

Best regards

James
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Old 21st September 2013, 02:46 PM   #370
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Hi James,

Using the clips for 6.3mm (diameter), they fit for 8mm also...
and selfmade holder.

some Pictures

Click the image to open in full size.

Click the image to open in full size.


Click the image to open in full size.

Best regards, Matthias
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