Tuning Pot Retrofit

The tuning rate on the SS-40 can be improved by using a 10k LINEAR pot with a 15K parallel resistor. In the spirit of continuous improvement and customer satisfaction, the Four State QRP Group is making that change beginning with the 2nd run of kits, which has already begun - PLUS providing a retrofit kit at cost  for those who purchased kits from the first run and wish to make the change. This page describes the retrofit, and the steps necessary to implement it.

The first run kits were shipped with a 5k audio taper tuning pot for two reasons. A 10K linear board mounted pot wasn't available, and neither was a 5K linear. So the decision to use a 5K audio pot (which was available) had to be made. The tuning rate was acceptable, but somewhat faster during the last half of rotation. Many builders have found the tuning rate satisfactory however, especially while employing a large tuning knob.

One of the keys to doing the retrofit without risk to the PCB is using Chip Quik. It's a low melting point alloy that can be added to a soldered joint. In the case of the PCB mounted pots the three joints stay molten, if heated sequentially, and the pot literally falls off the board. See the video below. You can also use a heat gun on low setting to melt the joints with Chip Quik on them.

Below are the steps for implementing the kit.

Step 1. Remove the 5k audio pot using Chip Quick.
Be sure you are removing the correct pot. It's the one closest to the BNC antenna connector. Click this link for a video to see how it's done. Then remove the excess solder with wick or a sucker to clear the holes.

Step 2: Solder mounting pins in place.
The kit contains 2 swage pins. Use a sharp pair of diagonal cutters to remove the short part of them above the collar. Insert them into the two outside holes just cleared of solder, from the BOTTOM side of the board. Solder them on the bottom side. Your board should look like this at this point. Step 3: Install the 10k linear pot over the pins.
Place the 10K linear potentiometer solder lugs over the 2 pins on the top side of the board with the shaft pointing away from the board. As in this photo.

Step 4: Solder the 10k pot into place.
If you have liquid flux available, use a small amount at each pin location to make the solder flow better. Carefully solder one of the potentiometer lugs to its corresponding pin while holding the potentiometer down against the PCB surface and pushed gently away from the edge of the PCB so that the potentiometer is aligned as far rearward as is will go. If you are happy with the alignment, solder the other lug, or reheat the first lug to more favorably realign the potentiometer. Once the outer potentiometer lugs are soldered, solder the center lug, note that it has no pin and is soldered directly to the pc board. When all of the potentiometer lugs are soldered, the soldered connections will look like this.

Step 5: Install R30
R30 is the 15K (brown/green/orange) resistor in the kit. It is soldered into position directly behind the potentiometer.
It is located here.

Step 6: Testing: Confirm that the potentiometer is correctly electrically connected to the PCB by measuring its resistance.
. None of the three terminals should be shorted directly to ground.
. Place one lead of an ohm meter at the left mounting hole for resistor R32 and the other lead at the anode (arrow) of diode D9 (nearest board edge). Confirm that the resistance varies from ~0 to ~10K Ohms as the shaft of the potentiometer is rotated over its range.
. Move the Ohm meter lead from D9 to the right mounting hole for resistor R30. Confirm that the resistance varies between ~0 ohms and ~5.9k as the shaft is rotated.

That's it! You're done! Enjoy using this great performing receiver.

Parts List.
1-Potentiometer 10K Panel Mount
1-15k 1/4 watt resistor, R30, brown/green/orange
2-swage pins
Chip Quick ~1" piece

Ordering Information: ... The total cost of this kit is $7 for both US and DX orders. Shipping costs are included in the price. Part costs total $5.

Or pay by check or money order (US dollars only) please make it out to "Four State QRP Group" and send to:
Terry Fletcher WAĜITP
1305 Casper Drive
Ottumwa, IA 52501

As always, thank you for supporting the Four State QRP Group.

Comments or Questions?