A New High Voltage Power Board For the Heathkit SB-200

This is Part 1 of a 2 part series showing the construction and installation of the Harbach PM-200 Replacement Power Supply in the Heathkit SB-200.

Harbach PM-200 PIC


Recently I purchased a used Heathkit SB-200 amplifier from the DELARA radio club and after letting is sit on a shelf for a few months, I fired it up and immediately noticed problems. With a fair amount of troubleshooting, I discovered the HV power supply board was definitely not up to snuff.

Here and here are a couple of thread on groups.io which detail the discussion. See my previous post, A Dirty relay on a clean Heathkit SB-200, which improved the SWR “Chatter” problem, but skated around the root cause of the problem.

High Voltage Supply Board Problems

The HV meter on the SB-200 would fluctuate widely, and occasionally swing all the way down to 0. The PCB showed visible signs of damage from a past modification to replace the HV capacitors and a couple of capacitors looked to have small “bulges” on the top. This meant they likely saw abuse in the past.

Existing HV PCB Board – Damaged

With that information in mind, I bit the bullet and purchased the Harbach PM-200 replacement module.

The assembly guide provided by Harbach was decent, and a lot of thought is put into making the assembly process easy for most skill levels. However, it lacks illustrations and small details to make the process easier for amateurs that may be new to electronics assembly. Here is my attempt to add some additional information.


Only a few tools are required for assembly, at a minimum, you need a good soldering iron with a fine tip point, wire cutters, needle nose pliers, wire strippers and tape. For reasons to become obvious later, keep the shipping box the kit arrives in do not discard it yet.

Optionally, a decent Multi-Meter, desoldering wick or pump will come in handy for component checks and cleanup if you make a mistake. These items are not required, but will help if you need them.

Tools Required

Any type of soldering iron rated 60 – 100W, with good temperature regulation, and a fine point tip will work fine for assembly . I use a Chinese made Auyoe 2901 I purchased a very long time ago which has given many years of reliable service.

I recommend using a small diameter, standard 60/40 Rosin core solder, as it is much easier to work with (I use .032″). Stay away from the lead free stuff, it requires much higher melt temperatures, does not flow well, and requires care to prevent component overheat during assembly.

Soldering Iron PIC
Fine Tip Soldering Iron

Needless to say, make sure you are working with a clean soldering tip and keep in clean as you assemble. I like to use a small wet kitchen sponge and rub the hot iron after every 15 – 20 solder joints.

Soldering Iron PIC
Fine Tip Soldering Iron with Clean Tip


Start by laying out all of the components, take inventory, and verify component values.

Kit Contents PIC
Kit Contents plus assembly guide.

Page #4 of the Harbach manual lists the components along with the reference designators where they are installed. If you have a multimeter, verify all components are to spec with a multimeter also. If you do not have a multimeter, a quick read of the component values printed on the device will suffice. For resistors, decode the color bands to determine if their value is correct.

Next, perform a quick inspection of the PCB, verify all pads are intact and no gouges or scratches are present.

Blank Harbach PCB

Assembly Steps

  • Bend all components leads using a set of needle nose pliers before insertion, this makes insertion and soldering much easier.
  • Start with the smallest parts first and then work towards larger parts. This prevents them from falling out or separating from the PCB when you turn it over to solder.
  • Recommended assembly order for components
    1. Resistors R7 – R9
    2. Diodes D1 – D8
    3. Resistors R11 – R13
    4. Resistors R1A – R6B
    5. Capacitors C1 – C6
    6. Blue Wire
Bent Leads PIC
Prep component leads

Do not pre-cut the component leads, insert the full length into the PCB and then solder before cutting. This helps hold the components into the board and allows for a perfect cut length.

Solder Leads
Solder the leads

When soldering, heat both the pad and wire at then add solder, do not overheat as it can damage the PCB pad and/or the component. After soldering , trim the lead as close as possible to the PCB.

Lead Clipping
Clip the leads flush

Resistors R7 – R9

Start by soldering R7 – R9 in place. Polarity is not important in this case so the components may be inserted in either direction. Page #4 of the Harbach manual indicates which component goes in which position.

Smallest Components

Diodes D1 – D8

Next move on to D1 – D8, polarity is important in this case, make sure the grey band on the diode is oriented as indicated on the PCB silkscreen as per the following picture.

Diode Installed PIC
Install Diodes

Resistors R11 – R13 and R1A – R6B

After installing the diodes, install R11 – R13 using the same procedure as R7 – R9.

Resistors R1A – R6B require special consideration. These must be mounted at least .25 inch above the PCB to allow for proper air flow and isolation from the PCB.

The shipping box the kit comes in provides an easy method to make a quick spacer.

Repurpose shipping box
Upcycle the shipping box

The thickness of the box measures .15 inch. By cutting two strips off of the cover of the box, a quick and easy .3 inch spacer can be made.

Spacing Strips
Make a couple of spacing strips

Cut a couple of strips and tape onto the PCB .

Spacers in place PIC
Spacers in place

Install the resistors over the spacer and solder into the board.

Resistors on spacer PIC
Resistors with spacers

After installing the resistors, clip the leads and remove the spacer. You should have a pretty consistent spacing off the board at this point.

Resistors with spacer removed PIC
Resistors with spacers removed

Capacitors C1 – C6

Install the capacitors C1 – C6 next, polarity is very important here, if installed incorrectly, they will likely explode. To identify proper polarity, find the gray band with black squares, the lead nearest to this band is the negative pin and should go into the round hole on the PCB. The lead closest to the black side is the positive will go into the square hole with a “+”.

Cap polarity PIC
Align Capacitor Polarity

Next, double check the capacitors match the picture below.

Capacitors installed PIC
Capacitors installed

Finishing up

Finally, strip a small section of the insulation off of the blue wire supplied with the kit and solder to the underside of the PCB.

Blue Lead PIC
Install and strip blue lead

This should be soldered into the hole marked “V”.

Final Inspection PIC
Final inspection of soldering

At this point, assembly of the kit is complete, inspect your work and verify solder joints.

Board Assembly Complete PIC
Board Assembly Completed

Left over components

You will have one lonely 15K resistor left over from the build. This will be used during the installation process and should be held onto for now.

Left over Resistor PIC
Left over part to use during install

In Conclusion

Your PCB is ready for install, which I will cover in Part 2 of this series.

73 – AE8Q

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