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Peavey XR 696F - I made a booboo

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  • #61
    Ah. I have MPSW42 and MPSW92 in my hand as I write. Eight of each.
    Education is what you're left with after you have forgotten what you have learned.

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    • #62
      Originally posted by Enzo View Post
      Ah. I have MPSW42 and MPSW92 in my hand as I write. Eight of each.

      Only 3500 miles away!

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      • #63
        Originally posted by Enzo View Post
        Ah. I have MPSW42 and MPSW92 in my hand as I write. Eight of each.
        Do you have various parts in candy dishes around the house for when a tech swings by to say hi? 😁
        Nosaj
        soldering stuff that's broken, breaking stuff that works, Yeah!

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        • #64
          Originally posted by jondoe View Post
          Well 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
          I 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.
          Experience is something you get, just after you really needed it.

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          • #65
            Originally posted by nickb View Post
            I 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.
            They 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.

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            • #66
              deleted
              Last edited by glebert; 11-21-2019, 06:17 PM.

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              • #67
                Originally posted by jondoe View Post
                They 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.
                Ah! In that case you've solved that problem at least!
                Experience is something you get, just after you really needed it.

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                • #68
                  Originally posted by jondoe View Post
                  Well 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
                  I hope those are not coming from China. Those MPSW42 & 92 are now extinct, hard to find, and probably being counterfeited.

                  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 Enzo
                  I have a sign in my shop that says, "Never think up reasons not to check something."


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                  • #69
                    Originally posted by nickb View Post
                    Ah! In that case you've solved that problem at least!
                    It's not like this is the only part that got fried in the unit.

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                    • #70
                      Originally posted by glebert View Post
                      It'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 g1
                      I hope those are not coming from China. Those MPSW42 & 92 are now extinct, hard to find, and probably being counterfeited.]
                      They are coming from a UK ebayer who has a great number of audio parts, mostly old used parts and new old stock. Fingers crossed

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                      • #71
                        Originally posted by glebert View Post
                        To 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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                        • #72
                          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".

                          Click image for larger version

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                          • #73
                            Originally posted by glebert View Post
                            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".

                            [ATTACH=CONFIG]56028[/ATTACH]
                            The Peavey cross ref gives 2N6557 for the SD7204. Here is the data sheet for it showing the package and the power rating.
                            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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                            • #74
                              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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                              • #75
                                I just found Q206 on the other side of the board is also toast, so I'm glad I bought 10 of them now!

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