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Old 2nd April 2009, 01:26 PM   #31
roender is offline roender  Romania
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Default Re: Re: Replacements for MJ15003/15004

Quote:
Originally posted by wg_ski

... You just can't run the temp as high with the plastic pacakge.
Which mean that they can not handle the same amount of power (SOA)
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Old 2nd April 2009, 02:37 PM   #32
wg_ski is offline wg_ski  United States
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Pulsed SOA in the s/b limited region where Tj<<150C is going to be very very close. That's limited by the die and the heat spreader which is copper in either case.
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Old 2nd April 2009, 07:35 PM   #33
roender is offline roender  Romania
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Did you ever sow how big is the heat spreader in TO3 capsule? It has almost two time the thermal inertia than TO3P capsule ...
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Old 2nd April 2009, 08:13 PM   #34
wg_ski is offline wg_ski  United States
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The copper coin in a TO-3 is actually a bit smaller than the copper TO-264 base. The TO-247 (3P) base is the small one.
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Old 11th May 2009, 10:16 AM   #35
sajti is online now sajti  Hungary
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Here is the prototype, under test:

Click the image to open in full size.


Sajti
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Old 11th May 2009, 12:34 PM   #36
sajti is online now sajti  Hungary
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One more picture, contains the drivers.
Click the image to open in full size.

Triple darlington stage, 1st: MJE15032/33 with 25mA bias, 2nd:NJW0281/0302 with 120mA bias 3rd:8 pairs FJL4315O/4215O.

Sajti
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Old 11th May 2009, 01:23 PM   #37
tinitus is offline tinitus  Europe
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I run a single pair of MJL91193/94 in 50watt monos
Sound quallity of the finest kind

They have driven a complicated 5way 2ohm with no problem
In 1ohm they got pretty hot, and obviously didnt like that, but survived

It was remarkable that despite the very heavy load, amps didnt loose anything in sound quality

Is your supply really only +/- 37Vdc?
I reckon that would be below 100watt, which means you will have a very tough amp

UPS, balanced thats very different
Though I thought balanced wasnt very good fore driving low impedance, as it will see 2ohm as just 1ohm
Which would mean that it will deliver the 900watt/2ohm into a 4ohm load, but might get into trouble below 4ohm
Sorry, maybe I have no clew what so ever
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Old 11th May 2009, 01:38 PM   #38
sajti is online now sajti  Hungary
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The rails are +/-36V. 2 modules will be bridged, and I will use tube driver.
2ohms load means 32A peak, which means 4A/MJL pair. I think, there will be no problem with that.

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Old 11th May 2009, 02:17 PM   #39
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Quote:
Originally posted by Jan Dupont
Hello sajti,

First you won't get 900W/2ohms with +/-37VDC rail Voltages.

Have said that, then I tell you that I have several times with succes used the MJL21193/94 as drivers in large output stages.
Use the MJE15032/33 as predrivers and either BD139/140 or MJE340/350 as pre predrivers.

I made that mistake on my first amp build and used +/-45v
The amp worked but at any decent volume clipped the transients.

Music is a very complex waveform.
Drums especially cause very large spikes.

I now use +/-60V and that seems to be a lot better.
Sadly the price of electrolytics rockets above 63V.
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Old 11th May 2009, 02:35 PM   #40
AndrewT is online now AndrewT  Scotland
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Quote:
Originally posted by nigelwright7557
at any decent volume clipped the transients.

Sadly the price of electrolytics rockets above 63V.
that's precisely why we specify 100W amplifiers and use just 1W of output power. It allows transients ten times the average signal voltage to pass unclipped.

His 900W into 2r0 proposal will allow 9W of average output and still retain the 20dB overhead for transients.

Those 63V caps allow one to use a 40Vac transformer.
170W into 8r0, or 310W into 4r0. I don't know what you would get into 2r0, but it will surely be much less than the 900W he can get from +-36/7Vdc.
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