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xrk971 19th May 2021 02:38 AM

What’s On the Bench Tonight (OBT)
I thought it would be interesting to have a thread where I could talk about what’s OBT (on the bench tonight) - or what do I have to work on. A good chance to show what sort of projects and stuff I am working on.

I also invite folks to post their stuff here if they want - especially if it involves stuff from my shop!

I know there are folks working on FH9HVX, Alpha Nirvana, SLBs, SFPs, Aksa Lender’s, Yarra’s, and Rockville speakers, 10F/RS225 TL speakers, foam core builds, etc. please share what you are working on Tonight!

To kick it off, here is what I will be doing: some SMT reflow soldering of the LU1014D power JFET (I think it is a SIT) TO-247 IMS adapter boards. These will be a test batch to check to make sure they work. There is a GB here - I won’t be running it and the boards can be ordered by anyone as the Gerbers are posted free for all to use.

Woofertester has sent me a batch of matched LU1014D’s to install on these boards. These aluminum substrate boards will allow these peculiar power JFETs to be mounted in an underhung fashion like a conventional TO-247 MOSFET. They should be much easier to use. Also, Nelson Pass is giving away a bag of these unobtanium SITs to they DIYA community. Woofertester is doing the matching and WG45 is handling the GB. Thanks to JPS64 for the awesome layout of this metal substrate adapter board. Thanks to Nelson Pass and Woofertester for the LU1014D’s, and thanks to WG45 for handling the GB that is off to a roaring great start. I can’t believe we have 101 pairs of these adapter boards on the interest list already!

So that’s What’s OBT for me.

What’s OBT for you guys? :)

xrk971 19th May 2021 04:35 AM

6 Attachment(s)
As promised... WOBT for May 18, 2021:

Installation of LU1014D's on TO-247 Al IMS adapter PCBs.

I am using MG Chemicals Sn63/Pb37 Leaded No-Clean Solder Paste with 20ga tapered plastic nozzle applicator. First a clean with isopropyl alcohol and paper towel. Applied paste, installed the LU1014D, 100R 1206 resistor, and the Samtec 0.200in pitch SMT header pins. The only fiddly thing was figuring out how to bend the legs to sit flush with the PCB. It took some practice but I figured it out. Using my trusty Lindstrom needle nose pliers to do a Z bend then snipping the legs off to the proper length.

Here is the setup:

Here is what the parts look like installed on wet solder paste:

Here is what they look like on the hot plate - IMS PCB's heat up almost instantly and really no need for the hot air from the top. The solder melted almost immediately. I used some tweezers to nudge the parts into good alignment as the surface tension moves them around a bit. I probably had too much past on the thermal pad:

Here is what they look like after reflowing at about 240C for 30 seconds. I cooled the pan off on a wet towel underneath while fanning the part with a piece of cardboard - all done:

Here is a closeup of the joints, looks pretty good and with nice fillets:

Connected it to a component tester and it show up as an N JFET - so all is good, I did not cook it :):

I guess the next test is to set it up with the gate (G) shorted to the source (S) pin and place a low value circa 1-2ohm power resistor between S and Gnd. Then apply regulated 3Vdc to the Drain (D) pin and measure the current across the resistor. Check to see that the heat is dissipating properly.

So this is looking promising - and I think that this is something an average DIY'er can do with a basic skillet and electric hot plate set to LOW.

This is a similar paste (smaller quantity for the average DIYer):

I actually used this one - a much bigger volume:

xrk971 20th May 2021 01:14 AM

WOBT - May 19, 2021: installing the LU1014D TO247 adapters onto a heatsink and testing thermal performance.

I mounted the heatsinks earlier today. Surplus HP CPU coolers and some M3 drill and tap, thermal paste, it’s looking really good.

xrk971 20th May 2021 03:43 AM

Thermal Testing of the LU1014D TO-247 adapters
4 Attachment(s)
I made a little rig with a screw terminal block and some 10w 2% cement filled crossover resistors (2.7ohm, 2.0ohm, 1.0ohm) from Source to GND, a 9k1 resistor from Gate to GND, and a regulated bench supply of 3v to the Drain. I monitor voltage across the Source resistor to check the bias current.

Here is the setup showing the GPC Instek 3020 linear bench PSU:

Here is a closeup of the TO-247 adapter mounted to the heatsink with a screw terminal block used to bring the wires to the pins:

Here is a closeup of the test setup showing the resisotors and Fluke 101 and 115 DMM's used to measure the voltages. Shown here is the 1.0 ohm resistor case at 7.3v Vdrain:
  • For 3.0v at the Drain pin and 2.7ohm resistor, we get about 0.35A and the device is barely warmer than ambient. The heatsink works really well.
  • For 2.0ohm, we get 0.48A at 3.0v and temps still very close to ambient.
  • Fort 1.0ohm, we get 0.93A at 3.0v and temps maybe 1 to 2C above ambient.
  • I decided to crank up the voltage to 7.28v at the Drain and got 1.52A and the temps rose. The device temp was 37C, the heatsink temp was 25C (ambient 23C), and the resistor was 62C. The heatsink looks like it was keeping its cool well at 8.6w dissipation:

So, I think that this demostrates that the IMS PCB adapter works very well to transfer heat from the device and is easy to use. I also see that the LU1014D can handle 1.5A bias current easily. This will be pretty handy and we know that we need about 5.75v across the Drain to Source with a 1ohm Source resistor to achieve a 1.5A bias current.

twocents 20th May 2021 12:40 PM

Stunning work and great photos X! Are these photos taken with a cell phone camera under artificial light (since you work at night when we sleep)? As a matter of interest - what kind of hot plate do you use? Is it a non-stick frying pan on an inductor stove?
Sorry for all the questions, but I admire your work.
BTW, my bench looks terrible currently - couple of unfinished projects nobody would like to see.

xrk971 20th May 2021 02:30 PM

1 Attachment(s)
Hi Twocents, thanks!

My camera is iPhone XR and lighting is overhead recessed flood light bulbs fitted with 60w equivalent LED bulbs 5200K color temp.

I recently cleaned my lab and bench. It got to a point where I couldn’t find anything and had to take a full day to clean. I bought 3 new shelves and a bunch of storage bins. That made a huge difference. Each little container contains a project BOM and parts. With 4 levels per shelf and each shelf stacked with 12 x 3 total shelves, I can technically hold 144 bins! :)

xrk971 20th May 2021 03:16 PM

I use a basic resistive coiled element “dorm room” single burner stove and an old non stick aluminum frypan/skillet.

Here is a video I made a few years ago of the hot plate / skillet SMT solder paste reflow of my PCA headphone amp boards.

SMT Reflow with Hotplate - YouTube

Kokanee 20th May 2021 03:43 PM

Nice work X, and thanks for the video.


egellings 20th May 2021 07:14 PM

That's quite a hefty heatsink for that.

xrk971 20th May 2021 07:59 PM

Not if we want to send 5Amps through it :)

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