DSP-610 ~ PA Build

Slow Power Amp.

I know this is on a slow track but progress is progress.



90% Complete Power Amp

 

 

It has been a while since I posted any progress on this build.  The main build took place, mostly on weekends between 9/1/2013  through 11/09/2013.  The board has a couple of interesting quirks...

TIP:  I used a Red Sharpie marker to mark uninstalled (DNI) components:



Note: C6 and C31 are Marked DNI Parts

TIP: Two soldering irons and a solder gun were also very useful in this build. Use two irons as heat sources  for removing mistakes (caps and resistors) to heat both pads at the same time.  I used the 100W gun to solder to the substantial ground plane.

RF Connection Mods.

First, the antenna jacks and RF layout is a bit difficult to figure out.  I put shorting jumpers on the path to allow one antenna for TX and RX.  This seemed the most straight forward for operations.

 

RF In Connector

Then I had issues with the 0.1" headers for RF connections.  I used an Xacto knife to scrape a couple pads for mounting the jack.  I tinned the pads and flowed a generous fillet of solder to the connector




RF In End-Launch SMA connector...

 

Antenna Connector

The antenna output is a vertical launch SMA.  I could not find a suitable connector. While an end launch location would have been more convenient, but I could not figure out an RF friendly placement.  There is a trace on the left-hand side of the board near the RF coils. 

Instead, I modified  a SMA connector by cutting off the mounting tabs. I then used a file to machine them flush (brass works easily) and used the existing antenna pad for the center pin.  The ground connection was made by scraping the blue solder mask, tinning the copper exposed, and "sweating" a fillet with a generous amount of solder. The ground connection is probably adequate.

The modified SMA connector is seen mounted in this picture.  It is pretty substantial and there is enough room for the connector, which will be a right-angle SMA plug:

New RF Connector near the White AXICOM Relay

If I would have planned ahead a little better, I would have done this before mounting the Relays and potentiometers.  I did not want to remove or melt them by trying to solder the left-hand side, and had to be extra careful not to melt the plastic on the pot. 

The Transformers and Coils...

Winding school. 

Count the turns on the inside of the toroid cores. Scrape and tin the wires.  The instructions are from the Soft Rock 50, plans you need to translate the part designators between the two different boards.

Coils (L7, L8, L9, L10 & L11)

The five  toroid coils were pretty straight forward, 3 with 7 turns of AWG #22 and 2 with 5 turns on T-50-6 (Yellow) cores.  The red enamel stained the cores a little when tinning the wire. NOTE:  L7 is a little tricky to mount, be careful there is a large ground via close to the pads, don't solder to that hole! Here are the winding specs. from the BOM;

L7,L8,L9 T50-6 CORE 7 TURNS #22 ENAMELED WIRE (6") AMIDON T50-6

L10,L11 T50-6 CORE 5 TURNS #22 ENAMELED WIRE (5")

The DSP610 PA Coil - Family Portrait

BP Filters

I did a manual sweep of the two filters.  I am not too happy about the 10 meter filter.  I need to check the values of the caps etc. It seems shifted to favor  12 Meters..

 

12M - 10M Filter Response

The plot of the 50 Meter pass filter looks pretty reasonable. Very much as expected.

6M Filter Response

 

 

Transformers (T1) and (T2)

 

These two were just as described:

"...[T1] on the PA board two loops of #18 wire through a BN43-202 Core. The wires are cut to 3" (75mm) each and stripped so that the insulation is 1 5/8" (65mm) long.'

 (Seen on right side with Red and White #18 wire);

"...[T2] 3" (75mm) length of RG-316, remove the outer jacket from one end and expose 0.75" (20mm) of the shield... Remove the outer jacked from the other end of the wire so that the insulation length is 1.5" (40mm)....Loop the wire through the BN43-202 core, unbraid  the remaining shield wires making sure that the shield on both ends of the wire point in the same direction. Strip the dielectric from the two center conductors. Tin and trim both shields and center conductors."

Seen on left side of the following picture. (basically, just a short length of RG-316 coax thru binocular core):
 

 

T1, T2 and L7 (Note via near L7)

Transformer (T3)

The mounting pad for T3 was not good. I applied a little too much heat and the pad lifted;

 After close examination it appeared that there was no electrical connection to the pad so I attached the rather substantial transformer to the board with a dab of 2 part  epoxy.

Transformer (T4)

The instructions are pretty clear for this transformer:

"Step 1:  Wind 2 windings each using 18" of #30 Kynar wire, (Green) 10 turns, one winding through each hole in a BN43-202 core,  ( I wound in same direction)..

Step 2: Cut 2 pieces of #22 Teflon wire, (I used Red and White) Strip the ends so that the insulation remaining is 7/8” long, the length of the bare wires is not important just so it’s long enough to go through the PCB. Tin the ends:"

T4 on DSP-610 PA

I did not really follow the mounting instructions, I just pulled the wires thru marked and stripped the lengths to match,  For the #22 wires I just measured the insulation and simply bent them to feed the leads thru the circuit board pads.

Transformer (L6) 

The description for L6 was pretty vague... (T1 = L6)

"..[L6] has 2 windings on a FT37-43 toroid: the primary consists of 2 turns of #26 enameled wire, stripped and tinned; the secondary is 13T of #26 enameled wire. It's best to wind the secondary first then wind the primary over the secondary. Try to form the leads to match the pads in the PCB..."

This was the most confusing part on the board  for me.  First a transformer labeled as an inductor? Anyway...The winding instructions are pretty straight forward but not a picture to back up the description.  Here is what I came up with...

 

L6 as Wound

The best way I see is to run "two" turns is to loop it (green wire) so it passes through the torrid twice with the most wire through the toroid, exiting on the mounting side. Forming the leads is also a little tricky. To make it match the schematic, after some careful study of the PCB I ended up with this:

 

L6 with leads Formed

 

The First Part Was...

 

Oh, yeah. the first soldered part on the KD6VKF DSP-610 project was L1 on 9/1/13:

 

 

L1 Installed

The next installments; Transistors, DC Bias adjustments, and compete the testing the board. Please Stay tuned!  (The KD6VKF DSP610 will eventually get done, really ☺)

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