We call this the Pine Board Project for a reason and that’s because we will actually be building a transmitter on a pine board, so you can see the circuitry. We want to try to not only build things, but we want to teach you what you’re doing when you are building it. You won’t just learn soldering. In this first project you will build a simple field strength meter, but that’s just the beginning. You will also build a 300 volt power supply, a microphone preamplifier, a transmitter, and a final tuner. Once all of that is done we will put it all together. The goal is to try to help you learn a little bit more about the schematics and how to build all while having fun.
*Special thanks to W4IQN for the graphics!
Caution: This is a fun project for all ages, but kids should be doing this with adult supervision due to the danger of high voltage. Anyone using these instructions must read the Heil Sound disclaimer before proceeding.
Project 1: Field Strength Meter
From HAMNation episode 289.
Parts and tools:
A pine board about 6 x 6 in.
Rosin core solder
Terminal strips (4s or 5s are best)
50k Potentiometer (a pot)
Meter 100 micro Amp
RF Choke 2.5mH
Antenna 19 inch piece of solid wire (coat hanger works fine)
Mount terminal strips on the pine board close, but not touching.
Every diode is polarized and as you reference the pictorial or the schematic you will see that band on the diode has to be placed in a very specific position with the band toward the plus side before soldering
Solder the choke into the terminal strips.
Solder the potentiometer from the choke/bottom terminal strip to the upper right side of the terminal strip.
Now it’s time to solder on the Meter. Solder the green wire to the upper right side of the terminal strip attached to the potentiometer and the red wire to the upper left side of the terminal strip attached to the diode. (picture)
Don’t forget to put your knob on your pot and attach an antenna. (picture)
The finished Field Strength Meter should look like this and now you’re ready to test it!
If you’re new to Ham Radio you might be thinking, “What the heck is Bob talking about (aka vocabulary terms)???” We’ve got you covered!
Potentiometer – (or a pot) is a three-terminal resistor with a sliding or rotating contact that forms an adjustable voltage divider.
Capacitor – a device for accumulating and holding a charge of electricity, consisting of two equally charged conducting surfaces having opposite signs and separated by a dielectric.
Diode – a device, as a two-element electron tube or a semiconductor, through which current can pass freely in only one direction.
Project 2: Power Supply
From HAMNation episodes 290, 291, 292, 293, 294, and 295
Parts and Tools:
3- electrolytic capacitor 20 mfd@ 450 v
2- 1k ohm 2 watt resistor
6X5 vacuum tube
Ceramic octal socket
2- solder-type terminal strips – 6 lug
3 lug barrier terminal strip
Pilot light socket
Pilot bulb (6.3v)
AC power cord w/plug
We started the Pine Board Project with a 6X5 vacuum tube rectifier to change the secondary AC voltage of the transformer to D.C. That tube is a half-wave rectifier. See below for a great video explanation from George Thomas about how and why this works. It produces about +150 volts of D.C. In part of the learning curve we create with the Pine Board Project, I introduce a full wave rectifier which is actually four diodes in one package that will
produce +350 volts in this circuit. There are two ways to do this. The first is to mount and solder the bridge into an 8 pin male plug, disconnect the center tap from ground – very important as the transformer center tap is no longer connected. Solder it to an unused terminal strip so it will not come in contact with anything. Plug that into the 8 pin socket that the 6X5 was plugged into. This +350 volts will now allow the 6AG7 to produce around 5 watts of RF output. The second way is to remove the tube socket, mount a 6 or 7 lug terminal strip where the bridge rectifier can be permanently mounted here the tube socket once resided.
Wiring before transformer and tube socket.
Project 3: Microphone Pre-Amp
We haven’t actually started this portion of the project on HAMNation yet, but for those that like to work ahead here is the parts list and the schematic.
Parts and Tools:
1 – 12AX7 tube
1 – tube socket (9 pin miniature)
2 – tube socket stand-off ½”
3 – solder-type (6 lug) terminal strip *
1 – barrier-type (4 lug) terminal strip
1 – electrolytic capacitor 10mfd/ @ 450v
1 – electrolytic capacitor 10mfd @ 25v
1 – ceramic disc capacitor 0.0047 mfd
2 – ceramic disc capacitor 0.001 mfd
1 – ceramic disc capacitor 0.001 mfd **
1 – ceramic disc capacitor 0.01 mfd
1 – ceramic disc capacitor 0.01 mfd **
1 – ceramic disc capacitor 0.047 mfd
2 – ceramic disc capacitor 0.1 mfd **
1 – resistor 1k Ω
2 – resistor 100k Ω
1 – resistor 100k Ω **
1 – resistor 1M Ω
1 – variable resistor 50k Ω
1 – variable resistor 50k Ω **
1 – variable resistor 10k Ω **
1 – knob for above
2 – knobs for above **
2 – ¼” phone jack
2 – ¼” phone plug
1 – switch, SPDT **
* trim length as necessary
** parts needed for the optional EQ circuit
Project 4: Transmitter
1 – 6V6 tube
1 – 6AG7 tube
2 – tube socket (8 pin octal) (B) P-ST8 250MT
4 – stand-off, ¾” – 1″ long for above (F) #58031
4 – solder-type (6 lug) terminal strip * (B) P-0702H
1 – barrier-type (4 lug) terminal strip (C) BB375-4
1 – electrolytic capacitor 10mfd/ @ 450v (B) C-ET10-450
1 – electrolytic capacitor 47mfd @ 50v (B) C-ET47-50
1 – silver mica capacitor 500 pf
1 – silver mica
1 – ceramic disc capacitor 0.001 mfd (B) C-D- 2000 .001
1 – polypropylene capacitor 0.0047 mfd (B) C-LD0047-630
1 – variable capacitor 365 pf, single gang (B) C-V365
1 – knob for above
1 – resistor 100 Ω
2 – resistor 22 kΩ, 1 watt
1 – resistor 56 KΩ
1 – resistor 100 KΩ
1 – RF choke 2.5 Mh
1 – DC filter choke 4 H, 50 ma (B) P-CF 22707
1 – coil: MFJ #404-0811-1
1 – crystal FT-243 type 3.885 MHz ** (E) 3885mHz
1 – socket for crystal (above)
1 – antenna jack (SO-239) (D) MFJ-7721
1 – alligator clip
* trim length as necessary
** For 40 meter operation, add a crystal 7.290 MHz
*** a kit of parts is available
(A) SND Tube Sales, www.vacuumtubes.com
(B) Antique Electronics, www.tubesandmore.com ***
(C) Radio Daze, www.radiodaze.com
(D) MFJ, www.mfjenterprises.com
(E) Amateur Radio AF4K, www.af4k.com
(F) Ace Hardware
Pine Board: Hobby Lobby “wood pile”
Shown above: 6AG7 Bottom
Shown above: 6V6