EF Johnson Viking 500 #2 - RT's Radio Home Page
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EF Johnson Viking 500 #2
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The latest project is yet another Viking Five Hundred. This unit will be a real challenge because no power supply/modulator unit came with it. The consensus regarding why there are so many orphaned RF units around is due to families of amateur operators who have passed on have no clue that the big, heavy box on the floor is a neccesary component to the transmitter unit on the desk. (Credit: Rodger, WQ9E). The units become separated, and the power supply will go a different direction than the RF deck.
This Viking Five Hundred has been restored on the exterior and was nicely done; in contrast, it is an electrical challenge on the interior. Strange modifications, circuits removed and others added. The first find was a hard-wired short on the 120 volt line; two broken switches, and the VFO board had burned. After replacing the VFO board, repairing the switches, removing the non-original wiring and restoring the missing circuits, the RF unit more or less "works" now but with low power output using good tubes. There may be more non-standard wiring yet to be found.
July 2025: After many many hours of finding and undoing oddball modified circuits , replacing deleted circuits, finding/re-facing the multi-meter, rebuilding the burnt VFO and repairing the audio section, the RF deck is nearly airworthy again. It easily does 300 watts using its old JAN 4-400A.
The new power supply is being constructed as time. permits.
Metering:
Here is the original multi meter. The face had been reproduced on cheap copier paper. It needed replacement.
The meters: Initially, the meters seemed OK, except the Cathode Current meter (left) suffered from maroon paint peeling on its interior. Once the RF unit was ready for testing, the multi-meter (right) was sluggish in movement and was sticking in position. Close examination revealed the meter face was a photocopy on cheap paper, and fibers of the paper were obstructing the needle. The paper was also yellowing, so it had to be replaced. Testing the meter, it is made by Honeywell and is electrically incompatible with the Viking 500. Fortunately, I have a Viking Valiant parts rig, and the Valiant meter tested identically to the good multi meter in Viking 500 #1 except the face was the wrong scale.
Disassembling and removing the original meter face from Viking 500 #1, the local Fedex/Office staff made copies of that meter face on premium cardstock. Cutting out the new meter face was straightforward, but without an accurately sized hole punch, creating the alignment holes in the new face to accept the locating dowels on the meter body proved difficult. The solution was creating the holes by carefully burning them out using a long-tapered soldering tip. 3M #77 spray adhesive was used to attach the new face to the meter.
The bezels of the meters were originally colored in the standard Johnson maroon. For whatever reason, the Cathode Current meter had been painted to match; however, this paint was flaking off inside the meter. The only matching bezels I had on hand were black Honeywell bezels; these do fit Johnson meters, so they were installed.
VFO Burnt by Chernobyl Resistor
The VFO had suffered from the degredation and failure of the infamous 18K resistor. In this case, the resistor must have shorted during the meltdown causing the 0A2 regulator tube to overheat and literally burn the phenolic VFO platform.
In Viking Ranger and Valiant transmitters, it would have been easy to replace the entire VFO unit from a donor transmitter. The Viking 500 is slightly different as its VFO also provides the mechanical drive for the auto-tuned RF stages. Ranger and Valiant VFO's lack this drive system.
The best fix was to replace only the phenolic board which carries the VFO coil; this donor board came from a Viking Valiant parts rig. The 0A2 socket was replaced due to overheating of the tube. It was labor-intensive, and the outcome was worth the effort. The repaired VFO works very well.
August 3, 2025: First contact/QSO on using this transmitter was with a ham whose opinion I trust. He indicated the audio was good.
To recap, I picked up an orphaned Johnson Viking Five Hundred RF Deck back in January 2025. It is beautifully refinished/re-screened on the outside, but inside, a nightmare of mods/changes were found. Thankfully, most of the original main components are in good shape. I am a vacuum tube radio enthusiast and not an engineer, and I estimate having about 60-70 hours into this transmitter testing, pondering, re-wiring, repairing, etc. to get it back to the original schematic.
Fast forward to July 2025, the transmitter is alive again and transmitting at full power on 40 meters. Audio was borderline acceptable but is now clean after finding a bad capacitor in the audio circuit. Now that it works, it still needs an alignment and neutralization. It had been “re-capped”, and the quality of that particular work is good. Judging from the capacitors used, it was likely done in the 1990’s, so the electrolytics will be replaced again before final testing of the audio circuit.
7-27-2025
Chuck, K1TLI is looking at getting a run of Viking 500 power supply chassis' made. If he gets enough interest, the cost will be reasonable. I am interested.
8-10-2025
Preparing to do an alignment, checking all bands, I tested each one for output as follows:
80 meters 400 watts
40 meters 350 watts
20 meters 350 watts
15 meters 100 watts
11 meters 60 watts
10 meters 100 watts
The transmitter responded well to the alignment. Power output per band:
80 meters 400 watts
40 meters 400 watts
20 meters 400 watts
15 meters 395 watts
11 meters 350 watts
10 meters 350 watts
Unfortunately, the PA Cathode meter was found to be the wrong meter. Indicated 190 mA is actually 305 mA on an accurate meter. Output maximum is still close to 400 watts on the lower bands at 305 mA.
Drat!
Just when it seemed I had this beautiful machine ready for the desktop, it became clear that the Cathode Current meter is not what it seems. Similar to the Multi-meter, it looks the part, is scaled properly, but it is not a 500 mA meter.
..........more anon.