"NOGA Twin Tube 80"
Instruction Manual
by
Mike Branca - W3IRZ



.....The NOGA Twin Tube 80 is a 2 tube 80 meter transmitter that can produce 1.5 watts with the simple 150 volt power supply. Upping the plate voltage to 250 will produce 7 to 10 watts. This transmitter is constructed on an Altoids tin and safely contains all voltages (except RF) within the tin. Two tubes are used in parallel in order to pull enough current to produce over 1 watt with the simple power supply. For the circuit a crystal controlled Colpitts oscillator was chosen because it works so well with pentode tubes. A capacitive voltage divider feedback arrangement is used across the crystal. A 3579 kHz crystal is supplied to check into the Boat Anchor bunch but a crystal socket is omitted and replaced with two short clip leads to accommodate the large variety of crystals you may run across. Keying is accomplished thru completing the cathode circuit. The plate tank circuit is parallel tuned and the high voltage is kept off the tuning capacitor (and the top of the chassis) by using the .01 uf capacitor in series. RF output is via a 4 turn link on the middle of the tank coil and the link can be slid down the tank coil to reduce the power if desired.

.....Start the assembly by preparing the Altoids tin by removing the hinged lid carefully. Set the lid aside as all parts will be mounted on the bottom and the tin will be used face down. This is to give room for the key jack and the RF connector on the edges of the tin. Using a chunk of 2X4 to support the metal start punching the holes with an awl or ice pick from the outside. The holes may be enlarged with increasingly larger sizes of phillips screwdrivers and by using the needle nose pliers to open the tube socket holes. Possibly one could use a Dremel tool to cut the holes with one of the rotary files. The punched holes are actually stronger because of the rolled metal serving as a reinforcement. Punch all holes before starting the assembly of parts including those on the front and rear. Note the pin position of the tube sockets then scrape the paint from the Altoids tin where the mounting ears contact. Using a solder gun or larger iron tin those 4 spots where you scraped the paint off Then tin both sides of the tube socket mounting ears. Now solder the tube sockets in place. Take two of the 4-40 screws and mount the variable capacitor. Mount the key jack and the RE jack.

.....Now we wind the coil. Start with the pill bottle (if there is any gummy label residue clean off with paint thinner if desired) and pass about 4 inches of wire into one of the lower holes, bend it and then pass it out the adjacent hole. Wind 32 turns closely in either direction. This will take about 11 feet and pass the end thru one of the upper holes. Again pass the wire thru the adjacent hole. Pass the end back thru the first hole again and down to the bottom and thru one of the bottom holes. You now should have a very neat coil with two wires coming out of holes near the bottom. Put a strip of masking tape around the middle of this coil. Now take two feet of wire and wind 4 turns on the middle of the masking tape. Twist the ends 3 or 4 times to keep the wire in place. This is the RE output link coil. One end should be 2 inches and the other end will be 4 inches. Now mount the coil with the two 4-40 screws and nuts orienting the wire leads towards the tubes.

.....The wiring is now started underneath the chassis. Since this is 80 meters nothing is really critical and it is supposed to oscillate anyway. All the tube pins are jumpered except pins 4. Note that some of the parts used in this kit are used or old so the leads will need to be scraped to make them shiny before they will take solder. Under the chassis the tube pins are numbered clockwise.

1. jumper pin l to l
2 jumper pin 2 to 2
3 jumper pin 3 to 3
4. jumper pin 5 to 5
5. jumper pin 6 to 6
6. jumper pin 7 to 7
7. as wired you can use the supplied 6AR5 tubes or 6AQ5 tubes (optional wiring to enable using other pentodes like the 6AK6 and 6AU6 as well as the supplied 6AR5 but not the 6AQ5; add a jumper from a pin 2 to a pin 7)
8. on one socket wire the 7 pf cap from pin 1 to pin 2
9. take the two short red wires and strip and tin both ends
10. solder an alligator clip to each red wire
11 pass both red wires thru the holes in the chassis; solder one to pin 1 of the closest tube; solder the other to the chassis; these clips are the crystal socket
12. take the 15K resistor (brown, green, orange) solder one end to the rear pin 1 and the other end to ground
13. take the 70 uh choke and the three 33 pf disc capacitors and connect them all in parallel leaving one lead from each end
14. connect one end of the choke assembly (stepl3) to the key jack and the other to a pin 2
15. on the side, between the tube sockets solder a small loop of wire for a cable strain relief
16. solder the smallest .01 uf capacitor from the key jack to ground
17. take the largest .01 uf capacitor and solder one end to the center rear panel; the free end is the B+ buss and three wires will be connected there
18. the last .01 uf capacitor has a wire attached with a piece of spaghetti on it; the short lead is soldered to the variable capacitor stator connection on top of the chassis; the remaining wire passes thru the hole and connects to a pin 5
19. solder a resistor lead (from step 12) from the variable capacitor rotor connection to the chassis
20. the tank coil wires are passed thru the hole with the top wire connecting to a pin 5 and the bottom wire connecting to the B+ buss (step 17)
21. connect a wire from pin 6 to the B+ buss (step l7)
22. the 2 inch link wire connects to the variable capacitor ground lug (if it has one) or is soldered to the top of the chassis; the longer link wire passes thru the hole and is soldered to the RF connector
23. the power cable is now prepared by taking the thick black wire and stripping and tinning both ends and passing one end thru the power cable hole and soldering to the chassis between the coil and the variable capacitor
24. take two pieces of wire the same length as the black wire and twist them together so that they will stay together, pass them thru the power cable hole, thru the strain relief loop (step 15) and solder each to a pin 4; this twisted pair becomes the 12 volt filament wiring
25. (optional step if it is desired to wire the filaments for 6 volts if, for example, a 6 volt wall wart is used; first jumper pin 4 to pin 4 then solder the twisted pair (step 24) to a pin 3 and a pin 4)
26. take the red wire, pass thru the power cable hole, thru the strain relief loop (step 15) and solder to the B+ buss (step 17)
27. at this point you are done and should solder any unsoldered tube pins
28. now you may re-attach the Altoids tin cover which becomes the chassis bottom plate: rubber feet may be attached if desired

POWER SUPPLY

The power supply should be built inside a plastic box to prevent exposure to AC and high voltage and it is suggested that the terminal strip also be within the box. The wall wart is used to supply the 12 volts needed by the series connected tube filaments and due to the weight should be tied down with a tie wrap or clamp. The capacitors can be tied down with lacing cord, string or tie wraps. All wiring can be done point to point.

1. The AC line cord black and white wires will be soldered direct to the AC pins of the wall wart
2. mount the terminal strip and mark 5 terminals as follows:GND-12V-12V-l50V-GND
3. connect the diode from the black wire (on the wall wart) to the plus side of the 470 uf capacitor with the arrow pointing to the capacitor
4. connect the 47 ohm resistor from the plus side of the 470 uf capacitor to the plus side of the 220 uf capacitor
5. connect the plus side of the 220 uf capacitor to the 150 V (B+) on the terminal strip
6. connect the green power cord wire to both ground terminals on the terminal strip and to both capacitor negative leads.
7. connect the 68 K resistor (blue, gray, orange) from the 150 V terminal to the ground terminal
8. cut the 12 volt leads of the wall wart but leave them long enough to wire to the terminal strip; connect the two wires to the 12 volt terminals on the strip

TESTING

Test the power supply by plugging it in and measuring the voltages at the terminal strip. Let the filter capacitors discharge; it will take a few minutes. Wire the cable to the power supply and plug in the AC cord. Now check the transmitter for ±150 volts at the B+ buss. Also check for 12 volts (AC) from pin 4 to pin 4. Again let the capacitors discharge. All OK; clip the crystal into the clips then plug in the two tubes carefully. There is only one adjustment in this transmitter, the air variable capacitor. Connect a wattmeter (with dummy load) to the output jack, connect a key to its jack, press the key and adjust the capacitor for maximum power on the peak using the maximum capacity. Or connect a 100 ma meter across the key and adjust the capacitor for the dip at the maximum capacity. If you were provided with a capacitor of 100 pf then you will note a peak (or dip) at near minimum capacity and it will then be tuned for 40 meters and a 40 meter crystal will work producing about the same power output as 80.

SAFETY NOTES FROM W3IRZ, MIKE BRANCA.

If your house is not wired with grounded outlets then it is suggested that an isolation transformer be used. However, if grounded outlets are provided, then there is no need for an isolation transformer. Let me explain: the use of a 3 wire power cord is a tremendous safety device. First the round pin (and green wire) is connected to the household ground and the radio chassis. The other two wires are tied direct (soldered) to the two pins of a wall wart which is mounted inside of a plastic cabinet. This wall wart provides the 12 volts ac for the tube filaments. Now for the HV a diode is wired from the black wire on the wall wart to the positive side of an electrolytic filter capacitor. The negative side of the filter capacitor goes to the green and chassis ground. Yes, this will put a bit of current into the ground wire in the vicinity or 40 to 60 ma. when the key is down so it is not serious, but it may be considered by some to be a violation of the electrical code and will trip any ground fault device so don’t use it in one of those (GFI) outlets. NOW the question: is it safe? - yes, absolutely! The code is designed to make wiring safe for any ignoramus - and it is. But that does not mean that that there are no other safe arrangements. Go to your electrical breaker box, take your screwdriver and remove the cover. Inside you will notice that the white wires, green wires and bare wires are all tied to the same ground buss bar as well as the service ground. Tell me what the voltage drop is for 50 ma in 150 feet of 14 gauge wire - let’s get serious. Now before you re-attach the box cover put a rubber mat on the floor, put on rubber gloves, get a large well insulated screwdriver and tighten all the screws that have wires attached. I have never found a box with no loose screws, usually at least half are loose. As they do not loosen in use it is a workmanship problem. Just think of all the radio noise that you have just eliminated. BTW if you read the NEC go to article 250-21(c) where it talks about temporary (ground) currents (only during key down for us) not classified as objectionable currents (intentional for us) but performing the intended safety grounding function. This description may very well make us totally within the code!

PARTS LIST - TX

1. 2- 7 pin miniature tube sockets
2. 2- tubes 6AR5 (optional 6AK6, 6AU6)
3. 3- 0.01 uf 500 v disc ceramic capacitors
4. 3- 33 pf 50 v disc ceramic capacitors
5. 1- 7 pf 50 v disc ceramic capacitor
6. 1- 15 K ohm 1/2 watt resistor (brown, green, orange)
7. 1- 70 uh l00 ma choke (larger - OK)
8. 1- 100 pf APC air variable capacitor (or smaller value with attached fixed cap)
9. 1- pill bottle measuring 1 inch at the bottom
10. 1- RF connector - RCA type supplied
11. 1- 1/8 inch key jack
12. 1- crystal 3579 kHz
13. 2- miniature alligator clips
14. 2- 2 inch pieces of red test lead wire
15. 20- feet of 26 gauge plastic wire
16. 2- feet of 26 gauge red plastic wire
17. 2- feet of 18 gauge black stranded wire
18. 4- 4-40 screws 3/8 inch long
19. 2- 4-40 nuts
20. 1- Altoids tin

PARTS LIST - POWER SUPPLY

1. 1- 3 - wire power cord
2. 1- wall wart 12 volt AC @ 500 ma
3. 1- lN4004 diode @ 400V
4. 1- 470 uf electrolytic capacitor 250 V
5. 1- 220 uf electrolytic capacitor 200 V
6. 1- 68 K ohm 1/2 watt (blue, gray, orange)
7. 1- 47 ohm 5 watt (use two 100 ohm in parallel)
8. 1- 5 terminal screw strip



Mike Branca
W3IRZ


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