EF Johnson Viking 500 #2 - RT's Radio Home Page

The latest project is yet another Viking 500. 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 do not realize the big, heavy box on the floor is a neccesary component to the radio box on the desk. The units become separated, and the power supply will go a different direction than the RF deck.

This Viking 500 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 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.

It is "a work in progress"

Metering:

Here is the original multi meter. The face had been reproduced on cheap copier paper. It needed replacement.

Copy of the correct

meter face on premium cardstock.

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 Viking 500 multi meter except the face was was the wrong scale.

Using the original meter face from the good Viking 500, the local Fedex/Office staff made copies of the 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. The Cathode Current meter had been painted to match; however, this paint was flaking off inside the meter. The only matching bezels on hand were black Honeywells; these do fit Johnson meters, so they were installed.

VFO Burnt by Chernobyl Resistor

The VFO had suffered from the degredation of the infamous 18K resistor that failed. In this case, the resistor must have shorted during the meltdown, s causing the 0A2 regulator tube to overheat and literally burn the phenolic VFO platform. In other Viking Ranger, Valiant transmitters, it would have been easy to replace the entire VFO unit from another transmitter. The Viking 500 is slightly different as the VFO facilitates the mechanical drive of the auto-tune for the RF stages. The other VFO's lack this drive system.

The best fix was to replace the phenolic board which carries the VFO coil and tube sockets. It was labor-intensive, but the outcome was fantastic. This VFO board came from my Valiant parts unit. The rebuilt VFO works very well.

A 40 meter signal from the VFO on the spectrum analyzer.

The New Power Supply:

Here is the topside view of the power supply chassis from a Johnson Invader 2000. It is in the process of being converted to operate the Viking 500. All components have been carefully removed from the chassis. It has some small areas of surface rust. Some sanding marks from previous repairs were found; some of these were successfully removed by the buffing wheel.

Underside view of the power supply chassis.

These are the original components from the underside of the chassis.

This transformer suffered a catastrophic event! It is not original to the power supply, and it has no center tap for the 2.5 volt secondary; this may be what led to the burnout. It will be discarded, and the new rectifiers will be solid state. Inrush current limiters will be installed at the 240 volt line to the high voltage transformer to limit the instatntaneous load at keyup. These tube sockets will carry the 811A's in the modulator.

To be continued.....