Plus 12 Conversion
Add The 12 Meter
Band To Your HR-2600 Or HR-2510.
One PC board (1 3/4" by 1 3/4") to mount the parts onto.
(Foil on one side only)
One 5 volt relay. Single pole double throw.
Two
trimmer capacitors-pc mount type (6-50pf).
One ceramic disc capacitor
(47pf).
One crystal at 21.995 mhz (Load 33 pf,Resis 20,Drive 2 mw,Tolerance
.005,Wire Terminals HC18). [This controls the 10 meter band].
One crystal at
17.995 mhz (Load 32 pf,Resis 24,Drive 2 mw,Tolerance .005,Wire Terminals HC18).
[This controls the 12 meter band].
You will also need a few feet of hook-up
wire. (Less than 1/16" in diameter).
You'll
notice that there are two circuit boards visible in the radio. One larger one
which is lower and to the rear of the radio and a smaller higher board closer to
you. Find and remove the 4 screws holding the smaller (upper) circuit board and
the 4 screws on the side of the radio, just above this circuit board. Once these
are removed you will be able to lift the board up and turn it on its side. Be
careful not to break any wires!
Now locate the 22 Mhz crystal (X302). Unsolder and remove it
from the board. In its place, solder two wires, one through each hole of the old
X302 location. Make each wire 2 inches long. Be sure to have a good contact on
the other side of the board!
Locate the DIM switch on the outside front of the radio. Notice on the inside of
the radio that EACH switch consists of 3 sets of 2 parallel pins. Count down 4
sets of pins from the top, Solder a 12" piece of wire here. (If the radio were
upright, this would be the bottom set of the DIM switch's pins). Be sure when
counting not to miss the top two rows, they are hard to see up near the top.
Once the wire is connected, put the board back in place and reinstall all of the
inside screws. Also, attach a 5 inch wire under the back right corner screw
before tightening it. This will serve as a GROUND WIRE for later use.
Refer to the next figure for the exact placement of the parts
on the board, and follow the instructions below. Also refer to the schematic as
needed. 
Building The Conversion
Board:
Insert all of the parts through the
NON FOIL side BUT ALWAYS COUNT THE ROWS AND HOLES FROM THE FOIL SIDE, STARTING
FROM LEFT TO RIGHT. (Ignore the 4 large corner holes).
Insert the two trimmer capacitors first. The parallel ends insert in the top
row, the other end of the capacitors insert in row 3. On the foil side of the
board, find the capacitor pins near the center of row 1 (the 2 closest pins-row
1 holes 4 and 8). Solder the 2 pins using solder bridges across the foil or use
a small piece of wire to attach the two together and solder.
Next, we'll install the 5 volt relay. It has 6 pins. The 2 that are separated
from the other 4 we will call pins 1 and 2 (left to right facing pin side of the
relay). The center 2 are pins 3 and 4. The bottom two are pins 5 and 6. Insert
the relay between the two caps with pin 1 in row 2 hole 6, pin 2 in row 2 hole
8. Pins 3 and 4 in row 4, pins 5 and 6 will be in row 5. Turn over the board and
solder pin 1 to the foil to hold it in place.
Insert the 10 meter crystal into row 6, holes 4 and 6. Connect one lead up to
row 3 hole 4 and solder to the capacitor at that point. The other lead connects
at an angle to pin 5 of the relay. Solder. Insert the 12 meter crystal into row
6 holes 10 and 12. Tie one lead to row 3 hole 12 and solder to the capacitor at
that point. Connect the other lead at an angle to relay pin 6 by using another
piece of wire and solder.
Now take the lead that you soldered to the left hole of X302, (front of radio
still facing you) attach the other end to the capacitor at row 1, hole 1 and
solder. Take the lead that you soldered to the right hole of X302, attach the
other end through row 2, hole 5, solder to relay pin number 1 (row 2, hole 6).
Take the Ground lead that you put under the screw earlier and insert the other
end through row 4,hole 10 and solder to relay pin 4.
Finally, take the free end of the DIM switch wire that you had soldered to the
inside front panel and insert it through the perf side of board in row 4, hole
6. Solder to relay pin 3, row 4, hole 7.
Testing Your Work:
Insulate the bottom of the conversion board with electrical
tape to keep the foil from shorting any of the 2510/2600 parts. Placement of the
conversion board should be as seen in the first figure. Reconnect the antenna
and power. Turn on the radio and press the DIM switch on and off, the relay
should click on and off. If not, recheck your work. With the DIM switch off
(Bright) you will tune across the 10 meter band.
When on 12 meters, the radio still displays 28 MHZ. For
example, if you want to tune to 24.95, set the radio to 28.95. With the DIM
switch on (light dimmed) you are really on 24.95 of the 12 meter band. Just
subtract 4 MHZ from the displayed number, all of the other digits will be
correct.
This last step should only be used if you experience distortion on the received
signals on the 12 meter band. Take the 47 pf capacitor and cut the leads to
about 1/2 inch. Solder one end to test point 306 (TP306). This is located to the
left and about 1/2 inch in front of X302. You must have a good contact here!
Solder the other end of the capacitor to the metal can of the coil right behind
TP306.
A frequency counter or a local ham can help you tune the radio back on frequency
on each band. Adjust the capacitors to set each band on frequency. The capacitor
connected to the 10 meter crystal, will adjust the 10 meter band, the capacitor
near the 12 meter crystal, adjusts the 12 meter band.
Remember, in the USA, the 12 meter band runs from 24.89 to 24.93 for cw and
24.93 to 24.99 for phone. And you need at least a General Class or better to
operate the band! 12 meters is an interesting band. Even if it sounds dead, get
on and give a CQ call, it is often wide open long after 10 meters has died.
Caveat: It is up to you to ensure that the radio
signal output of both bands meet your country's requirements for purity of
emissions. If you determine that the emissions are not up to standards you may
still want use the conversion for the purpose of listening to the additional
band.