Hello guys, need a piece of advice here... I want to replace the 2N3055 in a JLH2003 Class A with the recommended MJ15003. What do you think, should I use new ones, or old "original" used ones? Here are the links:
Free shipping 20PCS High Power Transistor MJ15003 MJ15003G TO 3 Fever Audio Power Tube|tube transistor|tube audio - AliExpress
https://ro.mouser.com/ProductDetail/ON-Semiconductor/MJ15003?qs=HVbQlW5zcXW2QH8jOZ6%2Fng%3D%3D
I kind of suspect the china ones as being fakes... What do you think?
Thank you,
Mihnea
Free shipping 20PCS High Power Transistor MJ15003 MJ15003G TO 3 Fever Audio Power Tube|tube transistor|tube audio - AliExpress
https://ro.mouser.com/ProductDetail/ON-Semiconductor/MJ15003?qs=HVbQlW5zcXW2QH8jOZ6%2Fng%3D%3D
I kind of suspect the china ones as being fakes... What do you think?
Thank you,
Mihnea
Fakes for sure but they could still be good, maybe even better suited to the application than bog-standard 2N3055. I suggest you look at JohnAudioTech's videos on the JLH class A amplifier, particularly where replacing the kit semis with the similar, genuine 2N3773 transistors caused quite a problem too. Class A audio amplifier kit test & review - YouTube
Generally though, replacing suspect semis in cheap kits is a safe plan, if you know how to tell if that just causes other problems or not. I don't believe the 2N1711 semis are genuine either and 2N2907 is not original spec. anyway. It seems obvious that this kit is more about shiny, antique looking metal parts regardless of performance.
DIYs with instruments and skills can test whether there are parts problems but not all of us can do that. The straightforward solution is just to use all genuine parts, including 2N3055, MJ15003 or other, similar 1-4 MHz old semis and that means dealing with reputable, industrial parts distributors, not Ebay re-sellers.
3DD15D?
Does it make any sense to try a transistor design from the region such as the 3DD15D when trying to be economical? I ask since I have had some success using things like the S9018 for other applications (oscillators). And I ask because I am hoping that designs from the region (that are economical) might not make sense to fake.
Has anyone tried these in a small JLH design?
3DD15D TO-3 NPN Power Transistors - 5A 300V/200V 50W Bipolar Transistor
But only 50W, and only 5A. Maybe too small. I wonder if it has a bigger brother.
10pcs 3DD15D TO-3 NPN Power Transistors - 5A 300V/200V 50W Bipolar Transistor | eBay
Does it make any sense to try a transistor design from the region such as the 3DD15D when trying to be economical? I ask since I have had some success using things like the S9018 for other applications (oscillators). And I ask because I am hoping that designs from the region (that are economical) might not make sense to fake.
Has anyone tried these in a small JLH design?
3DD15D TO-3 NPN Power Transistors - 5A 300V/200V 50W Bipolar Transistor
But only 50W, and only 5A. Maybe too small. I wonder if it has a bigger brother.
10pcs 3DD15D TO-3 NPN Power Transistors - 5A 300V/200V 50W Bipolar Transistor | eBay
3DD15 is a series of ISC (Inchange, China) semis. Check the Datasheets and look at the range. I don't see 3DD15D type there but perhaps it's a new product, a downgraded part that is offered cheaply or faked Chinese part! Now, that is an interesting concept 
3DD15 Transistor Datasheet pdf - Power Transistor. Equivalent, Catalog
There are better parts in TO3P packages if you want cheap semis. You can use other boards which suit these newer packages and are cheaper too. I use KTD1047 (marked K 1047 since it's a copy of 2SD1047 which Rotel used with 2SB817 in everything they made for many years). It sounds better to me than 2N3055 anyway. There's nothing wrong with TIP3055 either and they are cheap and reliable, from genuine new parts sellers everywhere.
3DD15 Transistor Datasheet pdf - Power Transistor. Equivalent, Catalog
There are better parts in TO3P packages if you want cheap semis. You can use other boards which suit these newer packages and are cheaper too. I use KTD1047 (marked K 1047 since it's a copy of 2SD1047 which Rotel used with 2SB817 in everything they made for many years). It sounds better to me than 2N3055 anyway. There's nothing wrong with TIP3055 either and they are cheap and reliable, from genuine new parts sellers everywhere.
You would need to do a lot of rebuilding to fit 2 pairs of T03 transistors in each channel of a typical stereo JLH amplifier. Is it worth that much effort and cost just to fit those extra TO3 transistors?
I don't look at the inside of amps when they work, only when they need building or repair so perhaps my perspective is different to others' before the novelty wears off.
I don't look at the inside of amps when they work, only when they need building or repair so perhaps my perspective is different to others' before the novelty wears off.
The TIP3055 is quite affordable at $0.74 each for quantity 10 at Mouser. So if that is a good choice I will try it. I see the KTD1047 in a number of my LJM projects such as the MX50SE, MX50X2 and the L20.5. However they seem expensive to buy at $3.70 for the 2SD1047 at Mouser (I didn't see the KTD1047 listed). I suspect it is affordable in quantity or at other resellers if you know where to find it. (Otherwise the MX50SE would cost much more.) I see them inexpensively on AliExpress but the ink marking does not match the laser marking on the ones in my LJM kits so who knows what is inside of a copy of a copy. Do you know where real ones can be bought?
I have been considering a series of comparison projects involving switching my KTD1047 devices with SanKen devices from Digikey and Toshiba devices from Mouser. (2SC6145 and 2SC5200) to see what I can notice. (Since I have read so many positive comments about them.) But perhaps the D1047 is already a very good device?
Years and years ago (about 34) I made my first amplifiers with just four transistors each from an old Motorola application note. I am trying to find that particular application note again (for fun) because I want to recreate those amplifiers to compare (for fun) against various kit projects I have made in recent years. Is there an archive somewhere of such old application notes? I unfortunately don't remember the number so I will need to do some digging.
Attachments
KTD1047 and KTB817 are KEC's (Korean) versions of 2SD1047 and 2SB817 and still in production but the SANYO originals are long obsolete and Sanyo's semi business is now On semi's. url]https://alltransistors.com/pdfview.php?doc=2sd1047e.pdf&dire=_update_bjt[/url]
Mouser sells STMicro's version of 2SD1047 only.
KEC's semis perform about half way between SANKEN's LAPTS and standard epitaxial power semis which still makes them quite good enough for class A but not the fastest needed for premium class AB where top quality Sanken power transistors are still the best way to go in conventional output stages. Pricewise, the Korean semis are hard to beat in either application. Not surprising; you can't buy them at low prices over the counter at your local industrial supplier so buy them where LJM kits are sold, if you follow the logic, but avoid the several other Chinese brands on offer that are usually marked D1047 and maybe with their brand mark etc. rather than K.....
A suggestion on cooling, FWIW. Use mica and white grease with these semis. The silicone rubber washers are fine for typical class AB but not up to serious class A heat with reliability. Good, dead flat and thin mica isn't a certainty nowadays so be careful who you buy from and get the thinnest you can afford or learn to properly split the stuff yourself.
Mouser sells STMicro's version of 2SD1047 only.
KEC's semis perform about half way between SANKEN's LAPTS and standard epitaxial power semis which still makes them quite good enough for class A but not the fastest needed for premium class AB where top quality Sanken power transistors are still the best way to go in conventional output stages. Pricewise, the Korean semis are hard to beat in either application. Not surprising; you can't buy them at low prices over the counter at your local industrial supplier so buy them where LJM kits are sold, if you follow the logic, but avoid the several other Chinese brands on offer that are usually marked D1047 and maybe with their brand mark etc. rather than K.....
A suggestion on cooling, FWIW. Use mica and white grease with these semis. The silicone rubber washers are fine for typical class AB but not up to serious class A heat with reliability. Good, dead flat and thin mica isn't a certainty nowadays so be careful who you buy from and get the thinnest you can afford or learn to properly split the stuff yourself.
Thank you for the warning on the Mica versus Silicon Rubber pads. I just bought a bag of the Silicon Rubber insulating pads to assemble some of my projects into more permanent (salvaged receiver) cases...
Does anyone have numbers on what sort of thermal resistance is expected for Mica and Silicon Rubber insulators?
I have a few Mica ones salvaged from the receivers but I will need to get more.
I am guessing the Silicon Rubber will be fine for MX50X2 and L20.5 but the class A and even the fairly hot MA9S2 are where I should get Mica I guess.
Does anyone have numbers on what sort of thermal resistance is expected for Mica and Silicon Rubber insulators?
I have a few Mica ones salvaged from the receivers but I will need to get more.
I am guessing the Silicon Rubber will be fine for MX50X2 and L20.5 but the class A and even the fairly hot MA9S2 are where I should get Mica I guess.
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Well I answered by question from looking at "sboa020" from BB (Ti) which is "MOUNTING CONSIDERATIONS FOR TO-3 PACKAGES".
They quote 0.4 - 1.0 C/W for Silicon Rubber and 0.3 - 0.4 C/W for Mica (with thermal grease) on page 4.
https://www.ti.com/lit/an/sboa020/sboa020.pdf
They quote 0.4 - 1.0 C/W for Silicon Rubber and 0.3 - 0.4 C/W for Mica (with thermal grease) on page 4.
https://www.ti.com/lit/an/sboa020/sboa020.pdf
I'm guessing that might be AN-484A with monolithic Darlington Power Outputs for outputs of 15,20, and 25W using MJE800 and MJE700 for 15W and MJE1100 and MJE1090 for the other two. I could not find this on line but I have a paper copy.
These designs are similar to that shown in figure 2 of the attached link - with the distinction that the voltage stages have been restructured with a wider range of power options - see https://conradhoffman.com/papers_lib/AN483B.pdf
In the above reference AN-484B, Q1 is 2N5087 PNP and Q2 is MPSA05 NPN
Thank you the reply and link.
Some parts of that application look a bit familiar but not quite the same. I think that is from the same era but perhaps a different application note.
I don't recall what the recommended device numbers were but they were not Darlington outputs. I do remember that in my incarnations I used MJ2955 and 2N3055 outputs and 2N5087 for the input device (pretty sure it was the PNP) and a general purpose PN2222 for the other transistor. I still have the bag of MJ2955 and 2N3055 devices but unfortunately after 34 years and many moves the amplifiers themselves are long gone along with the copy of the application note.
The input stage looked like the input stage of a "practical power amplifier"/JLH. But it was a Class AB amplifier with small individual heatsinks on the MJ2955 and 2N3055.
Modest power supply with 24VAC 2A Radio Shack transformer but a big bridge and a surplus huge white screw terminal Sangamd filter capacitor.
Output capacitor was a big blue (Philips?) axial capacitor.
Some parts of that application look a bit familiar but not quite the same. I think that is from the same era but perhaps a different application note.
I don't recall what the recommended device numbers were but they were not Darlington outputs. I do remember that in my incarnations I used MJ2955 and 2N3055 outputs and 2N5087 for the input device (pretty sure it was the PNP) and a general purpose PN2222 for the other transistor. I still have the bag of MJ2955 and 2N3055 devices but unfortunately after 34 years and many moves the amplifiers themselves are long gone along with the copy of the application note.
The input stage looked like the input stage of a "practical power amplifier"/JLH. But it was a Class AB amplifier with small individual heatsinks on the MJ2955 and 2N3055.
Modest power supply with 24VAC 2A Radio Shack transformer but a big bridge and a surplus huge white screw terminal Sangamd filter capacitor.
Output capacitor was a big blue (Philips?) axial capacitor.
AN-484A has simpler designs using 4 transistors. A pair of complementary Power Outputs and two for small signal, PNP for input and NPN for voltage gain - in that last respect identical to the JLH Simple Class A.
With 18V supply this gives 3W into 8R, and with 22V 5W into the same. There is a pcb layout for this.
With 18V supply this gives 3W into 8R, and with 22V 5W into the same. There is a pcb layout for this.
Perhaps it is AN-484A then. This does sound quite close:
I wonder where a copy might be found.
Or perhaps I can look at the PCB? Do you have a file or picture showing the PCB and schematic by any chance? For fun I would like to recreate the amplifier and compare the it with my more recent (and vastly more complicated) projects. It was a long time ago but I recall that these simple amplifiers sounded quite good.
I wonder where a copy might be found.
Or perhaps I can look at the PCB? Do you have a file or picture showing the PCB and schematic by any chance? For fun I would like to recreate the amplifier and compare the it with my more recent (and vastly more complicated) projects. It was a long time ago but I recall that these simple amplifiers sounded quite good.