Capacitors, Diodes, Resistor Networks

I've managed to put in a small number of hours over the past several days and the project is coming along, as usual, slowly but surely. I'm still checking each component's label and placement on the board two or three times before soldering, and then checking each soldered connection immediately.

Over the weekend, while waiting for the two missing parts to arrive (which they did in the morning USPS delivery on Monday), I wound T1 and T2, so they will be ready when I get there.

You can see in the picture that there were a large number of the small blue caps to be installed; fortunately, for all of them, I was able to follow the initial instruction, and didn't have to bend their leads at all.

Diode installation was no sweat. The instructions were very clear. The right side of the board is so crammed that several of the diodes were not labelled on the board at all, but were very clearly marked in the pictorial in the installation manual. The "check it twice" method caught the fact that I had initially put D4 in in the wrong direction; the cathode goes up, not to the right.

Here's what the KSB2 looks like so far. The right side is crowded. The holes for the cathodes of the two diodes at the extreme right side of the board are actually right at the edge of the board.

Transistors next ...

Adding the KSB2 SSB Adapter

A bit more than a year has gone by since I completed building the KPA100 and the building bug has bit again. I spent a big chunk of this winter someplace warm and I brought my K2 (sans the KPA100), and kind of wished I had had voice capability. So, I decided to add the KSB2 SSB Adapter to my K2.

The kit arrived by UPS yesterday in the late afternoon, and I did the inventory last night. The kit was complete except for one capacitor and one resistor; I wrote to Elecraft about it last night, and the parts have already been shipped as I write this (thanks, Elecraft!!).

Here's the kit, sorted into a variety of containers, and ready for assembly. As you can see, there's really not a lot of parts to this kit. However, as you can see here, the adapter board is pretty small, and there are a lot of small capacitors and 7 crystals, etc., crammed into a pretty small space. Should be interesting!

The KSB2 board is Rev. G, dated 2011. I started construction this afternoon; I couldn't get too far because the missing capacitor is one of the earliest parts to be stuffed (and I really don't want to get ahead of the assembly instructions). Assembly is prefaced with a comment about not needing to straighten the leads on small capacitors, but also to keep them no more than 3mm above the board. However, as the leads were formed on C30 and C36, there was no way the capacitors would be that close to the board; so I straightened the leads (and fortunately did not break them!).

KPA100 Completed!!

I haven't posted here for a while, but I have taken a few pictures along the way. Now that the project is done, I thought I would catch up here.

	Here's a look at the KPA100 board after the last component had been stuffed, and before mounting it on the heat sink/K2 cover. I put the big 800° tip, the one I use to assemble dipole antennas made out of #14 wire, on my Weller to solder the power transistors to the board. That did the trick very handily.
	When assembling T1 and T2, I scouted around the Web looking for pictures. I found some which were helpful, but I decided to take the pictures I wish I had found. This one shows the detail of how T1 was soldered to the board.
	Here is a detail of T2's installation, showing both how it is soldered to the board and, in particular, how C83 is mounted on T2's metal frame.
	Here is the final alignment and test setup. All procedures in this section of the manual went fine. I made one contact on 40 meters in this configuration. It also became immediately clear as I tested transmitting on the various bands that the KPA100 is quite sensitive to SWR. At this point, I reconfigured my good old Heathkit antenna tuner, which I had just been using to tune my 80/40 meter random antenna, to now tune all my dipoles as well. With SWR now 1.0 to 1 on all bands, the KPA100 happily ran at 100 watts with no power reduction.
	Here is the completed K2/100, with the antenna tuner now located in a more convenient place. I made a couple of contacts on 30 meters (HB9 and F5) and ran upstairs to get the camera!

So, I'm at the end of my Elecraft kit construction, for a while anyway. I'll see how the ARRL CW DX contest goes next month, and maybe look into building the KAF2 later this year.

I did not enjoy building the KPA100 to the same extent that I did the K2 and mini-modules. I found it to be fairly grueling, but I'm not sure why; maybe I just needed a longer break before starting construction, or maybe I needed to do it without the February contest staring me in the face. However, the KPA100 works fine "out of the box", and demonstrates again that Elecraft manuals are first rate; you just need to follow the instructions carefully (and especially so when an instruction is in bold font).

Constructing the power cable was a nightmare. Fortunately, this posting to the Elecraft K2 list provided some really helpful hints, especially about installing the fuse connector; I don't think I could have done it without Jay's suggestions. If I were to do this again, I'd buy the pre-assembled cable from Elecraft.

I'd suggest one change to the K2 build that would make KPA100 integration easier, and that is I would include P3 and P6 (RF and power connectors) on the K2's main board as part of the standard K2 build. I don't know what the statistics are on how many K2 builders go on to build the KPA100, but it sure was a nuisance having to disassemble and re-assemble the K2's heat sink to mount these two parts. I would have much preferred to install them as part of K2 construction.

There were no problems with clearance of all those capacitors on the bottom of the board; they all cleared the back of the heat sink with ample margins.

Two surprises: while doing the inventory back at the beginning, I discovered that KPA100 provides a DB9 serial port, allowing the K2 to talk to my computer. I built the serial cable last night and, sure enough, CTWIN can change bands on the K2! The other surprise came up fairly late in construction, and that is that KPA100 provides an on-board SWR bridge and metering. So, my recently built W1 is now off-line. However, I was still glad I built it, since I used it to calibrate the power and SWR metering on the KPA100; it was very handy reading exact power and SWR measurements on my PC!

Thanks to the parts and support folks at Elecraft for their fine help during construction. And thanks as well to Don, W3FPR, for his friendly and very informative support.

KPA100 Initial Test

	I wound most of the toroids and went back to stuffing parts into the KPA100 board. It turned out there wasn't much left to stuff to arrive at Initial Test; it was mostly a matter if installing all the ICs and a few of the back-panel connectors. Here's the test setup, including the modified ribbon cable (and accompanying modified plugs on the K2 controller board and the KPA100 board).
	And here's start-up status message ... that was a good feeling! And all voltage tests for Initial Test were well within spec.

Lots of KPA100 Capacitors

Having finally gotten through the large number of capacitors to be stuffed on page 17, I thought it was time for a posting with some pictures.

Man, there are a lot of capacitors in this project! Most of it was pretty straightforward, with some exceptions. C26 (a 33pf disc ceramic) lead spacing was wider than the spacing on the board and it was difficult getting the leads bent (and I was worried about breaking them, post-RFC9). Also, a little worried about space for all the inductors amid the forest of 1KV capacitors in the filter area.

There's quite a bit of detailed instructions on p. 15 about stuffing the .01 uf .1" lead spacing capacitors on the bottom of the board. The recommendation was to "remove any U-shaped bends" to ensure that the top of the capacitors are less than 3/16" off the board. Well, I think the bends are necessary to get the hole spacing right, so I left them alone. The caps are small enough so that they fit within 3/16"; see the photo.

The other instruction for the bottom-mounted capacitors concerned minimizing the amount solder used on the top of the board for these caps. This was necessary because the top-mounted relays all sit directly on top of the solder pads and have a very small, but consistent, clearance above the board. This was easy to do, and there were no problems later on with stuffing the relays.

Finally, I was unable to get RFC9 locally. I wrote to Elecraft's part line this past Monday, and had the replacement RFC in hand in Thursday morning's mail(!). Another great job by Elecraft staff and, for a change, by the USPS.

Taking a break from part-stuffing and am winding inductors, so they will be ready to stuff when I get there in the instructions.

RFC9

I stuffed most of the resistors and was getting a start on the RFCs. I fiddled with the leads for RFC9, trying to get it to sit flush against the board, long enough to succeed in breaking off one of the leads. It was then that I had a look at the e-mail reflector, did a search on "KPA100 RFC9", and immediately got a hit. Someone was wondering about the same thing and was referred to this document. Well, I wish a reference to this document was included in the KPA100 instructions. It seems that a number of years ago Elecraft stopped using sub-miniature RFCs in favor of miniature RFCs; however, the hole spacing on the KPA100 board fit the sub-miniature parts.

The document illustrated how best to form the RFC's leads, which I was able to do for the rest of the sub-miniature parts with no difficulty. You can see it best in RFC7. Well, on Monday, I'll go over to You-Do-It and see if I can find a replacement for RFC9; otherwise, I'll need to write to Elecraft.

One other construction note: I stuffed D1 to D8 on the bottom of the board, but the instructions did not say whether these are to be soldered on the bottom or top of the board. I looked back at the few bottom-mounted parts I had previously stuffed and, in each case, the instructions were explicit about soldering on the top. Since nothing was said here, I decided to assume that this meant "solder on the bottom", which I did.

Getting The KPA100 Underway

My plan was to start work on the KPA100 (Elecraft's 100 watt power amplifier enhancement for the K2) in December and the kit arrived via UPS this past Tuesday. I had kept all the little envelopes and ziplock bags from the K2 kit and decided to sort out all the KPA100 parts while doing the inventory. You can see the result in today's picture.

There aren't many resistors in this kit, but there are loads of capacitors. They are sorted out in the middle tray in the back, with the small lots in the envelopes to the right. As you can see in the right foreground, there will be quite a few inductors to be wound. All the relays, hardware (nuts, screws, washers, etc.), wire, speaker, fan, and so forth, are sorted out into ziplock bags and are back in the box, awaiting their turn.