Ah. I have MPSW42 and MPSW92 in my hand as I write. Eight of each.
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Peavey XR 696F - I made a booboo
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Originally posted by jondoe View PostWell I'll be damned, after looking through ebay I found some new old stock MPSW42 (10 of them), which come out at the same price as the SDS 7204 after you take shipping into account. I've ordered those
Is the SDS-7204 mounted on a heatsink or not?
I would go with the MJE340.Experience is something you get, just after you really needed it.
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Originally posted by nickb View PostI fear those uniwatt packages will overheat and die in short order. The original is 2W in free air, 10W on a large heatsink. The MPSW42 is 1 watt, 2.5 if you can keep the case at 25C or less.
Is the SDS-7204 mounted on a heatsink or not?
I would go with the MJE340.
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Originally posted by jondoe View PostThey were not mounted to a heat sink, just folded down a little out the way from it. MPSW42 was the part fitted to the amp, even though SDS-7204 is on the schematic.Experience is something you get, just after you really needed it.
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Originally posted by jondoe View PostWell I'll be damned, after looking through ebay I found some new old stock MPSW42 (10 of them), which come out at the same price as the SDS 7204 after you take shipping into account. I've ordered those
The SDS-7024 from Amplified Parts is the same style package as those MPSWs (TO-226). I'm guessing Peavey subs on that cross-x were the next size up that could handle the power.Originally posted by EnzoI have a sign in my shop that says, "Never think up reasons not to check something."
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Originally posted by glebert View PostIt's not like this is the only part that got fried in the unit.
I have quite the pile of dead parts, but at least I'm learning a few things as I go
Originally posted by g1I hope those are not coming from China. Those MPSW42 & 92 are now extinct, hard to find, and probably being counterfeited.]
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Originally posted by glebert View PostTo educate me, I don't understand how a 300V 10mA rated transistor can be a 10W device, that sounds to me like 3W or less, but I can't find any info other that that on these parts. I have never looked at one in person to know how big, etc. In this specific case, the max voltage C-E would be less than 115V, and the current should be less than 10mA (per original part spec), right? The MPSA part at 625mW might then be at risk of burning up, but 10W seems overkill.
The "300V 10mA" seems to be a typo on amplifiedparts. It's actually a 300V 500mA 10W ( 2W free air) part. It has a metal heatsink tab TO202 package.
The 10mA and 115V average for this circuit seem about right. I make the max voltage to be 205V due to the flying rails. It needs to dissipate around 1.2W on average in free air, quite a bit. The MJE340 data sheets I have don't give a figure for the junction to air thermal resistance nor do they give a figure for the max free air dissipation but I believe it will handle the 1.2W without a problem.
Maybe there is something in the 225 to 300V range that will do the job? I couldn't find anything new on RS Comps. Pickings seem quite few nowadays.Experience is something you get, just after you really needed it.
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This to me just doesn't look like it will fit at TO-202 package. I also don't see the 205v max voltage since the collector of Q106 is on a +25V rail. It is driving the base of a 1 A transistor (Q108) with beta over 100, so 10mA seems reasonable for Q106 current. I am happy to be wrong on this, just would like someone to explain it with something other than "the 7204 is a 10W part".
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Originally posted by glebert View PostThis to me just doesn't look like it will fit at TO-202 package. I also don't see the 205v max voltage since the collector of Q106 is on a +25V rail. It is driving the base of a 1 A transistor (Q108) with beta over 100, so 10mA seems reasonable for Q106 current. I am happy to be wrong on this, just would like someone to explain it with something other than "the 7204 is a 10W part".
[ATTACH=CONFIG]56028[/ATTACH]
2n6557-6559 ==SD7204.pdf
Thye more I look at I the less sure i am about the max CE voltage or the average power. OTOH if it is only 115V why go for a 300V transistor?Experience is something you get, just after you really needed it.
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Since we are still beating this horse, it seems odd that the schematic calls out "7204" not "SDS-7204". They don't drop letters for other parts, or if they do they list it both ways in the cross reference as an alternate name. Could it be two different parts, or maybe the same silicon in different packages?
As to why they would use a 300V part when a lower rated one would do? Usually it has to do with cost, and sometimes it is cheaper to use a higher rated part because you buy them in the millions. Assembly cost can be lower as well to reduce the number of different parts a board uses. There are people who's job it is to look at all the parts used across lots of different products and swap in something that will save a fraction of a penny.
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