OHR100a page
Building the Oak Hills Reserch OHR100a for 40m

I have wanted to build the OHR 100a for some time, but not knowing if my skills were up to the task I delayed. I finally decided to take the plunge and purchase the kit anyway. The OHR 100a is medium priced single band (a five band version is also available) XCVR kit sporting a full QRP gallon (adjustable power 0-5watts) along with a variable bandwidth filter, RIT with an output for a digital display. I chose the 40m version because in my opinion it is the best DXing band available especially for night-time/grayline DX chasing. The usual disclamiers apply. I'm just a very satisfied customer

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Now the OHR100a build

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FIRST THE BOARD ASSEMBLY

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I should also inform you that I'm using a flat bed scanner to take the pictures which causes them to be slightly unfocused sometimes. No depth of field or focus on a scanner

My kit arrived Friday 25 May 2007 three days after I ordered it. The first order of business is to inventory the parts that way I don't get a surprise from missing a part then having to wait for a missing part to be delivered. Inventory complete, no missing parts. Here is the PCB. Beautiful isn't it?

view of the top[L],view of bottom [R] solder side

Right click on picture for a larger view

Now order a large pepperoni pizza and while your waiting for it to be delivered read the construction manual again fully. When the pizza is gone you now have the perfect box to store the OHR 110a in when your not working on it and the corrogated sides of the box are are really super for holding the leaded components


1.5 hours tonight

I was able to work on it for about an hour and a half tonight. Installed the diodes in the first few steps along with the IC sockets RF chokes/inductors and test points
NOTE: When installing the IC sockets it is easier to use a small piece of scotch tape to hold it in place when you solder '''ONLY TWO CORNER PINS''' then apply pressure on the socket and reheat the pins. Generally you'll feel the socket snap in (down) giving you a firm and level fit. Now solder the remaining pins.

I prefer to work slower than most. I only install one component at the time. Like the carpenter I measure it thrice and cut (solder) it once. Less mistakes that way. As I populate the PCB I try to make it like reading a book by placing the first significant color band to the left to right and top to bottom on those parts installed vertically. It makes trouble shooting easier. Using a Hi-Liter I also check it off the overlay sheet if one is available. Just another way of double checking my work.HI.


2.5 hours today, four total

As you can see I double and triple check everything. That way it 'ALMOST' eliminates mistakes. Each solder joint is inspected and when needed reheated.

Each resistor is checked for value using a DMM then installed. I measure them because my 60+ year old eyes are unable to tell the differance in some of the color bands (brown and violet and sometimes differant hues of red and orange). Then check it of the list and mark the overlay.

Steps 1.1 on page 3 through 1.14 on page 4 have been completed requiring 4hours of work.


Steps 1.15 on page 4 through 1.23 on page 5


Another 2 hours added to the build for a total of 6.


Steps 1.24 on page5 through steps 1.42 on page 6


Another 2 hours for total of 8.


Steps 1.43 on page 6 through step 1.63 on page 7
ON STEP 1.50 DO NOT GROUND THE CRYSTAL CASES......
I checked with Marshall on this to confirm that they should not be grounded. [RC]


Another 1.5 hours tonight for a total now of 9.5

I skipped step 1.64 for now. I'll come back to it in a little bit


Steps 1.65 on page 7 through step 1.73 on page 8

Add another hour now 10.5


Winding the bifilar toroidal transformers for T100 & T101.
Notice: The wires ARE NOT TWISTED TOGETHER JUST PARALLEL
I checked with Marshall on this to confirm that they should not be twisted together[RC].


NOTE: When installing the molex connectors it is easier to use a small piece of scotch tape to hold it in place when you solder '''ONLY THE CENTER PIN''' then apply pressure on the molex plug and reheat the center pin. Generally you'll feel the plug snap in (down) giving you a firm and level fit. Now solder the remaining pins.

Steps 174 though step 177 on page 8 have been completed with the exception of step 1.64 which installs the PA (Q101) and the heat sinks for Q101 and Q100


Total build time is now 12 hours

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NEXT THE CHASSIS ASSEMBLY

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Steps 2.1 through step 2.7 on page 9. Total build time is now 13 hours


The large black object towards the rear are the heat sinks for Q101 & Q100.

Step 1.64 has been completed. PA and heatsinks installed. Total build time is now 13.5 hours


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FINAL BOARD ASSEMBLY FOR 40M

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Ready to begin the 40M assembly. I re-inventoried the parts for the 40M band just to be certain.

The board in now complete.

Total build time now 15 hours.

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FINAL ASSEMBLY

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Final Assembly is complete. The complete build time is 16.5 hours. That does not include the time spent taking pictures and documenting this build.

Smoke test and alignment are all that remain

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Smoke Test

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You could say the smoke test failed! No smoke was released. There is good strong audio signals and all controls seem to work properly.

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Alignment

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Since I do not have the correct test equipment to do a proper alignment I boxed the 40m OHR100A and sent it to Oak Hills research. I received an email telling me the alignment was completed within a couple of hours after receiving and on it's way back to me. Outstanding service Marshall.


It was aligned and returned to me. No issues were found a great kit and a lot of fun

RC KC5WA