6AG7 6L6 CW Transmitter for 40 Meters.
VFO or Crystal Controlled.
R1 = 56 K
R2 = 22 K
R3 = 5.5 K 10 watt
Note: This is used to reduce the B+ voltage down for the 6AG7.
This value will vary. This is the value that used based on my power supplys B+.
I used 3 of a 33K, 2 of a 22K in parallel, to arrive at my needed 5.5 K.
R4 = 18 K
R5 = 18 K
RFC1 = 500 uH choke
Note: You may not need to use this RFC. I had to use it to stop a parastic oscillation. The choke is in series with the
key, at pin 5 of the 6AG7. This value is not critical, most any value will work.
RFC2 = 2.5 mh
RFC3 = 2.5 mh
MA Meter = 0-150 ma
L1 = 23 turns # 20 ga. enam. close wound. Wound on a 1 inch form. See text.
L2 = 18 turns # 20 ga. enam. close wound. Wound on a 1 inch form.
L3 = 6 and ¾ turns #20 ga. enam. wire close wound around L2. See text.
V1 = 6AG7 Tube
V2 = 6L6GC Tube
Power Supply Notes:
******* HIGH VOLTAGE *******
******* BE EXTREMLY CAREFULL *******
If you have any doubts, get a qualified helper.
This project contains
VERY HIGH VOLTAGES
******* BE SAFE *******
After a 33-year absence from Ham Radio, I wanted to become active again. The 6AG7 / 6L6 CW transmitter is a result of much help and encouragement from the Glow Bug Net. Two years ago I saw Gary's WD4NKA webs site showing a schematic of a MOPA Transmitter, the 6AG7 / 6L6. The circuit shown here is a variation of Gary's circuit, with a "Tuned Stage" which allows for VFO operation. I received much help from "EVERYONE" on the Glow Bug Net at one time or another. Originally it was a 5-watt transmitter. Now with a better power supply I boast 20 + watts output with 34 watts input, and VFO or crystal controlled. In the early days of this project Gary hung with me, and in the later days Ken W7EKB who e-mailed me back and forwards with excellent help as to how to make a HG10b VFO to work with it. I would have never figured that out. I Thank Michael, NØXY for the VFO. Adding the VFO is as my son says "Sweet". I am not good at listing Thank you's, because I don't know where to begin, and not to forget all of those excellent web pages that Bry has posted. I wish that I knew how to thank everyone for all of those very FB posts that have me the ability to do such a project as this. This is my radio. I don't use anything else. I also want to thank my 15 year old son Zachary who wrote all of this html code for this web page. My biggest surprise after getting back on, is that they have taken all of the tube tester out of the drug store. I have as I write this 215 rag chew contacts that I have made with this transmitter, using a dipole antenna, and a DX-160 Realistic receiver. I live in Va. And I have worked to California, AZ, Washington State, TX., the Mid West, the Central US, and all of the North East, the South, as far East as France, Puerto Rico, Barbados in the West Indies, and all over Canada. All on 40 meters CW. I have only 11 state's to go for WAS.
L1 is 23 turns of # 20 ga. enameled coated wire close wound on a 1-inch form, with C12 attached across it.
I constructed this coil on a 1-inch plastic medicine pill bottle. At the top of the bottle I attached a mica trimmer capacitor to the top of the medicine bottle. I mounted the mica trimmer capacitor by tying several turns of small size string to hold the trimmer in place. Then taped the sting tightly to the bottle with clear tape. It really held it strong. I then attached one end of the trimmer to one end of the bottles coil and the other end to the coils other end. I mounted L1 on the topside of my cake pan chassis, near the back behind the 6AG7 and the 6L6. I ran the two wires from the coil through two holes in the chassis to the respective connections. One to the hot side of the coil connection, where C6 and C7 connect. The other end to ground. You can also use a variable capacitor (miniature is best) if you have that instead of a mica trimmer. A rating of 0 to 50pf is best, but other values can be substituted. Too large of a value will make it difficult to adjust the trimmer (C12). The purpose for the tuned stage is to "Tune the stage," this allows for the VFO to work. I had to add this tuned stage before my VFO would ever work. The tuned stage will create the maximum output for your transmitter.
L2 = 18 turns of # 20 gauge enamel coated wire.
L3 = 6 and ¾ turns of # 20 gauge enamel coated wire.
1.) The coil is wound on a 1-inch coil form. I have found that a medicine pill bottle works fine for the form.
2.) First wind 18 turns (close wound) to make the L2 windings.
3.) Center L2 on the coil form and tape in place. Clear Scotch tape works well for this.
4.) Next use a piece of manila file folder to make a round tube that will wrap over the L2 windings that are already on the coil
form. The new manila folder tube must be able to slide back and forwards across the L2 windings. Tape the L3 manila
folder tube together so that it will stay in a tube like form.
5.) Slide the L3 coil form tube on your coil form, covering the L1 windings. Now wind 6 and ¾ turns of wire across the L3
tube. Tape the L3 windings in place on the tube. Remember to tape so that the L3 coil will slide across the L2 coil. You
will need to be able to move L3 for adjustments for max. Power output.
6.) L2 and L3 are now complete.
1.) Connect the L3 windings to the RF output connector. S0 239.
2.) Connect the L2 windings to the output stage of your circuit.
3.) With the coil form mounted you are now ready to adjust for max. RF output.
4.) Connect a 50 ohm dummy load watt meter to the SO 239 connector via a 50 Ohm coax cable
5.) Momentarily key down. As you key down, observe the RF output and SWR on the wattmeter.
6.) Caution: Do not hold the key down for long periods of time. This is to prevent tube damage.
7.) Again with key down, adjust L3 by sliding it back and forwards to obtain the max. Power output at the lowest SWR. Mine
had full output with a flat SWR reading.
8.) Adjust C12 for Max. RF output. Re-check the L3 to L2 adjustment. Then Re-peak C12 again for Max. output.
9.) I did my adjustments with the variable capacitor C13 pre-set about half way. C13 may have to be re-adjusted.
10.) You now should see a dip on your MA meter, which correspondly equals Max. output.
11.) Having made the above adjustment, the output stage is now tuned for use with a 50-ohm antenna.
1.) I strongly suggest the usage of a balanced antenna system such as a dipole cut
For the CW portion of the 40-meter band
that you will use. This will reduce the Likelihood for out of band signals. I use a dipole like this fed with RG8 coax and it
works extremely well. My antenna is at 30 feet; I also use a 1 to 1 balun in my dipole. The coax connects directly to my
transmitter. I do not use a tuner. The thinking here is to have use a properly made antenna, rather than using an antenna
tuner to "make" it work.
1.) Not shown in the schematic, but I have two homemade choke coils to rid parasites, it is made of 5 turns of wire around a
47 ohm 1 watt resistor. One is in the plate and one the grid of the 6L6GC.
2.) I do not have any key clicks or stange wump sounds when I key. I constantly get 5-9-9 reports, and comments about
how good the signal sounds. Then I tell them it is a homemade tube transmitter. It makes for a good QSO conversation
piece. And constantly the phrase "I can't believe it", "It rally has a good tone".
3.) Terminals 1 and 3 on the 6AG7, and terminal 1 on the 6L6GC are grounded.
4.) In the photo you see two variable capacitors to make C13. Please note that the first capacitor is not connected. The rear
variable capacitor is the only one being used. The rear capacitor is a 120 pf.
5.) In order for the HG10b VFO to work, the VFO must be wired for cathode keying.
6.) Note: RFC 1, 2, 3 are air wound chokes, Not Torid type RFC chokes.