K3 Audio Upgrade Mod

[MontyS]

I would argue for the piggyback approach.   Use a pair of "sprung" tweezers that can grasp the SMT resistor at a comfortable angle.  (I use a 1/8 inch chisel tip iron for almost all my work - gets in and out very quickly compared to a smaller tip.) There is plenty of space around the two resistors. Set the iron at 700 degrees, cooler than normal.   A drop of solder on the iron tacks one end of the piggyback resistor.  Then a proper quick, neat solder job on the other end, and lastly clean up the first end with a proper solder job.  The iron never spends more than a split second on the connection - being deliberate and speedy is important to avoid dislodging the original part.  Looks neat.

 

Monty K2DLJ

The second part of the kit involves shunting two resistors with 51 ohm resistors,  and here also Elecraft gives two options: one is to solder 1/8w through-hole resistors onto the IO board, and the other is to solder two tiny SMT (surface mount ) resistors piggy-back onto existing SMT resistors. The kit comes with both kinds of resistors.  I elected to do the SMT version of the mod, and here I’d recommend that owners opt for the other method. I don’t see any advantage to doing the  SMT version. It takes a very steady hand, a very small-tipped soldering iron, and very good eyesight to piggy-back the two SMT resistors into the circuit, and I just don’t see the reason for the hassle. It would take five minutes to install the through-hole resistors, and the result looks quite clean and neat.  I’d recommend also that Elecraft delete the SMT option from the instructions. Took me about 30 mins to install the SMT resistors, probably about half that time to install the through-hole ones.

 

73,

 

Jim W8ZR

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[P.B. Christensen]

> "I would argue for the piggyback approach.   Use a pair of "sprung" tweezers that can grasp the SMT resistor at a comfortable angle."

 

At first, I detested working with SMT parts.  I slowly got over it and have developed a certain comfort level but I almost need to meditate first as the iron is warming up.

 

For me, a magnifying headset is a must.  Like most of you, my ability to work very closely on PCBs stopped nearly on the day of my 40th birthday and since then, my near vision has slowly gotten worse.  I now wear bifocal contact lenses, but the magnifier is still needed for SMT work.

 

Also, I need to limit my caffeinated coffee intake before working.  There is no way I can work with the iron and parts while I'm caffinated.  Way too much shaking.  

 

A well-lighted area and a good "mood" environment is also a must.  I almost never conduct SMT work with family anywhere nearby.  It's too easy to loose my focus and concentration -- and mistakes start escalating.

 

Regarding the K3 AF audio mod: I had no hesitation in removing the old SMT parts and directly replacing them with new values.  Arguably, the "piggy-backing" attempt is more difficult since you're not working against a flat surface, like the PCB.  Also, the area around the PCB's solder pads will be a bit more forgiving if alignment of the part is not perfect.

 

Somewhere on the web, an ingenious fellow developed a slick "third hand" for SMT work  The device is clamped to the edge of the PCB and pivots much the same way that we used to adjust a crystal radio's detector by varying the catwhisker arm position and tension on a piece of galena.   The end of the catwhisker is then pressed upon the SMT part to retain tension while the left and right hands are applying heat and solder.  Wish I new where to find one....

 

Paul, W9AC

 

 

   

 

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[Alexander Ponomarenko-5]

Good afternoon,

After replacement pair of these resistors there are any changes in work
of a linear output?

Any results of changes in a graphic kind are welcomed. Thanks!

73! Alex UR5LAM
K3/100F #0568
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[AC7AC]

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[Bill W4ZV]

P.B. Christensen wrote

Somewhere on the web, an ingenious fellow developed a slick "third hand" for SMT work  The device is clamped to the edge of the PCB and pivots much the same way that we used to adjust a crystal radio's detector by varying the catwhisker arm position and tension on a piece of galena.   The end of the catwhisker is then pressed upon the SMT part to retain tension while the left and right hands are applying heat and solder.  Wish I new where to find one....

Make one!  http://www.al7fs.us/AL7FS5ATSprint2.html  (2nd pix down)

...and   http://www.qsl.net/n5ib/surface_mount/

73,  Bill

[DaveL G3TJP]

Bill, W4ZV wrote:

 

Make one!  http://www.al7fs.us/AL7FS5ATSprint2.html  (2nd pix down)

...and   http://www.qsl.net/n5ib/surface_mount/

73,  Bill

Thanks, Bill.  I heartily endorse this little device.  I built mine from a wire coathanger, a couple of fishing weights, a toothpick and a two-screw coupling cut from a choc-block connector.

 

After a wee bit of practice, I was happy to work with 0805-size components and larger.  I built a 23cm preamp for another amateur that used 0805's and it worked just fine.  I do use an Optivisor as an aid to my ageing and very short sighted eyeballs, but can honestly say I'm at ease with 0805s.  Solder paste, I believe, makes life easier due to its stickiness, but as it has a limited shelf-life and is rather expensive I have only heard stories of its being used successfully.

 

For SMT chip removal I've used a length of fine enamelled wire in a loop under pins.  As each pin is heated, the loop is pulled and as solder melts, the chip leg is lifted clear of the PCB.  I've never damaged a PCB doing this.  I believe Chipquik low melting point solder is very good (Wood's metal?) to aid removal by flooding the pins with the special solder, which remains liquid for a considerable time.  I believe there are special clean-up techniques using their flux to get PCB pads clean.  For soldering fine-pinned components, I just flood the pins with solder and then use solder wick to remove surplus.  Works fine for me.  For two or three connection SMTs I use two soldering irons and then a bit of solder-wick, pre-coated with additional flux from a flux pen, to clean up the pads.

 

I know this is tempting fate, but I can't remember the last trace I lifted, it's so long ago.  Just be careful and patient and allow yourself time to THINK about the approach you are using for each and every circumstance.  As amateurs, we are unlikely to be under serious time constraints when soldering, so don't rush into anything.

 

73  DaveL  G3TJP

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