THIS is the transmitter that earned the very first Novice WAC (Worked All Continents) with just two crystals! This is the most basic a transmitter can get and still deliver good performance. It features a 6AG7 crystal oscillator/buffer/multiplier and an 807 final RF amplifier and covers 80 through 10 meters. It can be either screen modulated by a Johnson accessory 250-40 kit for less than $13. You could even plate modulate it, if you could build or buy a suitable modulator, once you got your General. The transmitter itself sold for less than $55, within reach of even a high school kid. This was one of the transmitters I considered back in the late 50s, when I thought about upgrading from my 6L6 single tube 80/40 rig. The one thing that deterred me was the problem of mistuning the final plates to the second harmonic and getting 40 meter out of band signals. (Two times 3.7 was one of the frequencies OOs and the FCC monitored at the time). I was also considering the Globe Chief. For only $5 more, you got two 807s and twice the power. I eventually wound up with a kit Eico 720, with a little financial help.
See page 2 of this E. F. Johnson Catalog: http://www.rlinwood.com/family_webpage/pix/radio/equipment/efjohnson_cat957.pdf
The Adventurer gets high marks (4.8 out of 5) in spite of its reputation of mistuning by inexperienced operators. Many rigs of that era had the exact same problem. Here are some reviews:
A novice aged 13 actually made DXCC in 1958 (KN4RID) using low power Johnson equipment. Remember that Novices had only one year licenses (not renewable) with CW crystal control only 75 Watt input power privileges on 80, 40, and 15. But 1958 was the legendary sunspot cycle (19) that fired the imaginations of many young ham operators. Even today I remember it fondly, if only from the stations I heard. Alas, my father owned a TV set with a 21 MC IF strip (no 15 meters for me) and I had a ground mounted vertical with no radials (no high angle radiation for 80 meters). But the bands were so hot that I could do W1AW practice after school with only a Regen set. At night, 80 meters was bedlam; phone was a cacaphony of heterodynes and CW was not much better. At night, 40 meters was inundated with foreign broadcast so badly that I took one of my valuable crystals apart, made a slurry of Bab-O cleanser, and ground it between shards of window glass panes to move out from under the QRM. One of my friends got a Heathkit VF-1 and used it as a Novice. He spent less on the VFO than I had tied up in my crystal collection. I sent endless CQs and tuned the Novice band looking for an answer. He showed me how to quickly make contacts sending E S E (dit, dididi, dit) and waiting for "dit dit". Once you found someone who was listening to your "shave and a haircut", you could exchange calls and get on with the contact. The same friend started getting advertising mail with his new Novice call letters printed on the mailing label. He immediately got on the air using that call. I waited until the official license arrived from the FCC about 3 weeks later. At my age, this is probably my last Sunspot Cycle. Good memories. But you did not select this page to read the ruminations of some old fart; you want to get your Johson Adventurer on the air. So here we go.
This article will first get the Johnson Adventurer operational and make some improvements. I will show how to rebuild the original Johnson Adventurer slide switches. There are photos of the process. A second section will ready it for AM phone operation, with a home brew push pull 6L6 plate modulator which can be used for any small transmitter. I may clone the rare screen modulator accessory just for fun.
Remember that most of these Adventurers were built from kits by Novice operators. Workmanship was not factory grade with a QC department like commercial rigs. But that was true of Heathkits as well. This was an affordable E. F. Johnson radio, presumably a step up from the competition. Solder blobs instead of solder connections are common. Burned plastic wire insulation from careless soldering iron operation rule. Sometimes it gets so bad, the whole rig has to be gutted and rewired. I think this is what happened to the Adventurer shown in photos on this page: http://www.rlinwood.com/family_webpage/linkpages/ham_radio/Rig_Pages/johnson_adventurer_transmitter.htm
W0UI collects Johnson equipment and has some very well preserved specimens. I suspect his rig was fully rewired as I have described. The TVI supression chokes near the modulator connector are not stock. A craftsman did the wiring harness and added the RF chokes. The front panel is perfect. Unfortunately, like a lot of my equipment, mine is a limited budget operation. So it was a rescue radio. The front panel was already spoiled with white paint along the top and two patches near each tuning knob. I imagine that someone used those patches for a writing surface to log the correct settings to avoid the 40 meter harmonic problem mentioned earlier. I covered the white patches with black electrician's tape for the time being. The expense of a new front panel is not within my budget. The stock meter bouncing around is terrible. I have a nice WW2 surplus meter to put in the hole, 200 uA full scale. The high/low loading control switch could not be repaired, and the loading condenser range did not work out well for my 80 and 40 meter operation. And the stock rig doubles in the final to get 10 meters; that works surprisingly efficiently. I may leave that alone. This poor radio was thrown across the room some time in its life, judging from the bends in the transformer ears. The pilot lamp had been removed for a toggle switch for AC power to replace the failed stock slide switch. The meter switch was on its last legs. The stock circuit puts over 600 VDC on that cheesy slide switch. The thought of it arcing to ground and wiping out the meter scared me. So the meter is going to measure CATHODE current after I get done, to remove the high voltage from the switch. Even the meter was badly off zero, probably due to having been thrown across the room. I used a magnet to magnetize the metal case of the meter, just to get it on scale. Cheap trick, but it works!
I do have a technique for repairing these slide switches, so stay tuned. This radio may wind up with a 24 VAC filament transformer and a 6159 instead of the 807. I have a bunch of these tubes which are basically a 6146 with a different filament that I can use up in this radio. But before the Restoration Police jump me for hacking up a collectible, this was not a candidate for a full restoration anyway. Fortunately, my philosophy is that I own radios to operate them, not to have a museum. So hot rodding it and driving it around with no muffler and no hood, painted primer coat gray, is no problem for me.
Just getting it running was the first order of business. It never ceases to amaze me when people start the cosmetic restoration or shotgun wholesale replacement of capacitors before doing some intelligent troubleshooting to see if the radio is even a candidate for restoration! Here is my procedure for the initial test of a vintage radio. You are welcome to watch the process, and see if anything you observe is useful for your workshop.
I tested the tubes first. Everyone working on tube equipment should shop for a tube tester for their workbench (see my article on workbench equipment for vintage gear). I have several tube testers with a variety of sockets and roll charts that cover all the tube era. The 6AG7 and 807 were tired, and the 5U4 was nearly shot. But they were functional enough for initial testing. Again, get it running first before in putting new tubes which can be damaged during the repair process.
I tested the filter capacitors. (Get a capacitor checker, see the workbench article). They were marginal, with a "pimple" of corrosion on the end. Definitely got to swap these out eventually.
I tested for shorts from the AC line to ground for safety with an Ohm Meter before plugging it in to my Variac and Isolation Transformer. (You DO have a Variac and Line Isolation Transformer equipped with a GFI outlet on your workbench, right?) In a real pinch, you can start up a radio and form the electrolytic capacitors with a line cord with a 110 V incandescent lamp of correct wattage in series with the radio under test. My Variac setup has such a bulb in series with the outlet. The lamp can be shorted out with a front panel switch once the radio seems to not catch fire when first turned on. This limits the current into the radio, and the lamp brightness gives a rough measure of the current drawn. My Variac setup has a Voltmeter and 5 Amp full scale AC ammeter. I unplugged the 5U4 to just test the power transformer. This poor radio was sitting in the back of a pick up truck in the rain overnight before the ham fest. I took off the cover and put it in front of my living room gas space heater, to warm it up and bake out the moisture for a week before attempting to put power on it. With the lamp in series with the AC line, I brought up the voltage on the transformer primary to 30 VAC. Happily, the AC on the secondary of the transformer measured about 1/4 of the value shown in the instruction manual. I ran it up to 60 VAC primary, then full 120 VAC, and let it sit there to see if it would hold. OK. Transformer good! I also tested the filament voltage under load with the 6AG7 and 807 plugged in. Just high enough on modern line voltages to cause concern. But I have a fix for that, to be shown later. I performed basic Ohm checks for shorts on the test points in the manual. Next step!
I plugged in the 5U4 and cranked up the Variac voltage to 60 VAC line input. The 5U4s take a lot of time to operate due to filament warm up. The DC output came up to about half the instruction manual voltage spec. No fires or shorts on the DC. Series lamp not too bright, and current on AC ammeter low. I edged the Variac up to 90 VAC line input. The Adventurer filter condensers started fizzing and smoking, but I now knew the radio was worth working on. Based on experience with these radios, I first only replaced the output filter condensers. This changed the power supply to a CHOKE INPUT filter. The CONDENSER INPUT filter produces about 0.9 times the AC RMS voltage of the transformer. The CHOKE INPUT filter produces about 0.65 times the AC RMS voltage of the transformer. This lower voltage should suffice for troubleshooting purposes, and reduce strain on the tubes and other components during initial tests. The original Johnson 8 uF capacitors are rated for 700 VDC. The voltage (key up) with older line voltage is about 680 VDC. Not much of a safety factor. I went for two 450 VDC 50 uF in series with equalizing resistors, for 25 uF effective capacitance at 900 VDC. The equalizing resistors came from a huge box of 180K 2 Watt resistors that I picked up at a swap meet. I use them up on everything. The capacitor input filter specified key up and key down voltages were all over the map. Running the VF-1 VFO off the Adventurer might be better with a Choke Input filter, which inherently has better regulation. Anyway, with power back on, everything seemed OK now. Oops! The R8 resistor for the 6AG7 was open; life must have been difficult for that poor tube. I replaced the bad resistor and then......
I plugged in a crystal and tried it out, and it did about 20 Watts input on 40 meters, but the high/low loading switch was intermittent. The stock meter bounced around so badly that the only legitimate way to tune it up was with my Jetstream Wattmeter set to the 30 Watt scale. About 10 to 12 Watts output, depending on tuning and crystal activity, even with punk tubes in the radio. Real progress! In fact, that is about the way I used it for the Antique Wireless Association Rollins CW QSO party. I worked Puerto Rico on 40 and lots of DX on 20, with lowered B+ and nearly dead tubes. Of course, I had a VFO and good antennas. These days, nobody seems to tune for a rock bound signal, even in the boat anchor rallies. But back to the repairs.
The next issues to address were the nasty slide switches and the AC wiring. This radio had a fuse in one side of the AC line and a switch in the other. The wiring went along the front panel, which could have implications for TVI and safety. The last owner had removed the pilot lamp and put a toggle switch in the hole to replace the failed AC power slide switch. There are three of these switches in the Adventurer. They are longer in dimension than any switches available these days. I will show how to repair the slide switches now.
Remove the defective slide switch. The photo shows the toggle switch in place of the pilot lamp. The rebuilt slide switch goes back where it belongs and the toggle switch comes out.
Here is how to fix the slide switch. Dismantle the original switch. It is hosed anyway. Use a pair of tin snips to remove all but the front of the slide switch. Using a Roper Whitney #5 hole punch, make holes in the old bracket for the the rivets to mount the new DPDT slide switch. You DO have a good set of hand tools and drills for your workbench, right? I love this tool because the holes do not wander as they do with a drill.
Using a rivet tool, install the new switch onto the old switch front piece you have salvaged. Then it goes into the front of the chassis of the Adventurer. This preserves the original look of the Johnson Adventurer using modern slide switches.
Wire the two sections of the new slide in parallel to increase current rating and reliability on the AC power location. I also reinstalled a pilot lamp in the original location. Be sure the rivets have the flush side of them facing the front when you rebuild the switches. I elected not to rebuild the loading high/low switch. I changed the loading condenser to a higher value one that did not need a parallel fixed loading condenser with a switch. The new loading condenser also had wider spacing, since I planned to use plate modulation later. I also rearranged the wiring of the AC so that the fuse and switch were in the hot wire, and installed a 3 wire grounding plug and cord. I removed the large coils of red wire that comprised the AC line TVI filter. I replaced that with a toroid salvaged from a TV set, for better filtering and to make room for other components. I routed the wiring from the AC power switch along the RF output coax and rear of the chassis (instead of the front of the chassis).
I replaced the 5U4 tube with solid state diodes. There is a 100 Ohm 5 Watt resistor in series with them to limit surge on power up and keep the HV in spec. Often people do not use such a resistor when they solid state a power supply. This value can be calculated from the forward voltage drop and rated current found in any good tube manual. Often, good tube manuals give the value as effective forward resistance. Simple math, Ohms Law, and the Power formula that was on the Novice exam, but many ignore it. I used the 5 VAC rectifier filament winding in series with the primary of the transformer to reduce the 6.3 VAC filaments to the correct value. It also reduced the plate voltage, which was a good thing in this design, if I went back to a condenser input high voltage power supply later.
I had only one of the original slide switches that was OK after cleaning it up. I installed it in the meter circuit. But the meter slide switch had over 600 VDC on it in the original circuit. That was unacceptable. I removed the original R5 from where it was and moved it to the cathode of the 807. I also shortened up the lead on the screen bypass condenser and grounded it directly to the metal spacer that held the tube socket. The pointer in the photo below indicates the bypass capacitor and new ground lug. The old ground lug appears in the photo nearby with a red/yellow striped lead of the high voltage transformer winding center tap. You can see how much it shortens the leads of the bypass capacitor. This should contribute to better transmitter stability. I also trimmed the value of R5 with a parallel resistance to make the plate meter read correctly (photo 1254 near the front of the tube socket on a terminal strip)
While I was on the subject of transmitter stability, I directly grounded the filament bypass and shortened up the lead on the cathode bypass capacitor as well. I then installed a heavy ground wire that went to the chassis and joined to the screen grounding scheme as well.
The screen resistor was replaced and rewired to the accessory socket on the back panel in such a way that it could be separated for either screen or plate modulation later. This also would allow an external tune/transmit switch that would allow for adjusting the grid drive without the plate being off resonance. This saves the final tube from stress. It could have been provided in the original design, but remember this is an economy rig. I used a 22K 10 Watt in the final configuration. For the QSO party it was a bit higher to reduce the input power below the 25 watt limit to put it in the correct power class.
The meter wiring is cleaned up as shown in this picture. The smaller 100 Ohm 5 Watt resistor for the 1N4007 rectifier surge protection is near the rear apron of the chassis.
I replaced the original 2 gang loading condenser with a 3 gang unit. The odd angle of the new tuning condenser is because the mounting holes lined up and the cabinet fit this way. This eliminated the need for the loading high low switch, which was hopelessly shot. I also put a small black transistor heat sink on the plate cap of the 807. Note that the lead from the plate cap to the parasitic supressor resistor and coil combination must be VERY SHORT or the efficiency is severely reduced on 10 meters.
This is a view of the oscillator 6AG7 and its coil, which were OK.
The cabinet was not too badly trashed, but white paint had also been applied to the rear.
The previous owners had put a decent coax connector on the back panel, but it was cracked. I replaced that and removed the RCA jack that had been installed for a VFO. The leads were unshielded and ran past the finals right next to the output RF connector. What were they thinking? I installed a ground screw and wing nut back where it belonged. Most all surviving Adventurers use coax cable to the output connector, although originally it was only a wire. This was a low cost rig.
The radio no longer looked much like the original Johnson Adventurer Pictorial Photo in the manual:
But then, neither did the inside of the one posted by W0UI. Mine was not nearly as neat as Woody's. But it did have some major improvements for safety and stability.
The original schematic and my modifications were different too. I took care to wire the accessory socket in such a way that it could be used with a screen modulator or a plate modulator. I eventually want to play with it both ways. Be aware that the input power with a plate modulator is about 50 Watts. The input with a screen modulator is only about 12.5 Watts or less. This is 1/4 of the maximum power. Remember that the peak power of an AM transmitter is 4 times the resting unmodulated carrier power. A high quality screen modulated transmitter can be used to drive a linear amplifier. This is how a Heathkit DX-60 is often used these days. Remember the DX-60 was originally $82.95 new. The Johnson Adventurer was only $54.95. Add the screen modulator accessory for $12.95 for a grand total of $67.90. You did not have to buy the modulator to use the Adventurer as a Novice; you had to buy the whole rig with the modulator up front from Heathkit. This is why Johnny Novice in 1958 often wound up with the Adventurer. Many more of the DX-60s survive.
No article on Johnson Transmitter repair would be complete without a comment on how to repair the missing white pointer on the knobs. I use a Q Tip Swab shaft, cut to length, and glued into the hole where the Johnson pointer often falls out. Get swabs with stiff larger shafts, not the cheap ones. If you are careful, you can make it look almost original. For a more accurate restoration, buy the real thing from:
If you were ambitious, you could have a home brew plate modulator with your Adventurer using a scrounged TCS modulation transformer from surplus outlets. This would put you well ahead of the DX-60 for phone performance once you got your General license. Here is the information from the manual on tune up and adding external modulation. Note the explicit cautions about tuning to avoid 40 meter harmonic output when operating on 80 meters. Lots of people were using end fed wires instead of coax fed dipoles those days. Wire was cheap. Coax was expensive. The manual also describes how to connect a VFO. DO NOT use the Adventurer for powering the VFO. The B+ goes from 680 VDC key up to 450 VDC key down with condenser input filter. Even with a choke input filter, it will cause chirp. Heck, the rig even chirps a little when using crystal control. But this is a starter station. Enjoy it for what it is. Run the VFO from a separate DC and filament power supply to avoid problems with chirp and allow the VFO to warm up separately from the transmitter to avoid drift.
We have covered a lot of ground. The Johnson Adventurer project is not done yet. I will show you HOW to replace the Johnson Adventurer meter with a better unit. The 6L6 push pull plate modulator and maybe a clone of the screen modulator is coming. The interface for a VF-1 VFO will be done. The Viking 122 VFO is very nice, but the Heathkit VF-1 is cheaper. We are going to stick to the theme of affordable radio for the beginner. So stay tuned.