EF Johnson Viking 500 #1 - RT's Radio Home Page

The E.F. Johnson Viking Five Hundred transmitter was produced during the late 1950s through about 1964. The AM/CW transmitter was designed as two interconecting units, the RF deck and the separate power supply/modulator unit which normally rests on the floor; EF Johnson lists the total weight at 173 pounds. This is a photo taken shortly after bringing it home and prior to any cleaning. Sources indicate production of the Viking 500 was limited to 865 units, so it is fairly rare. The transmitter employs an Eimac 4–400A tetrode tube in the RF final; plate modulation is provided by a pair of RCA 811A's. The transmitter has a single sideband mode that requires incorporation of a separate SSB exciter unit.

In January 2023, this Viking Five Hundred was found on Craigslist.

The underside of the power supply as found.

This is the completed power supply, underside of the chassis.

The major change/mod is the use of radial lead capacitors for the high voltage instead of those with axial leads.

The rationale for not using axial lead capacitors:

1: Axial lead electrolytics are expensive.

2: The radial lead capacitors installed are around $4.00 to $6.00 each and have better ratings, including longevity.

The new capacitors are lightly clamped into place by a square-sectioned plexiglass rod; radiused notches were cut in to cradle the capacitors. The notches are felt-lined, and there is a strip of felt under the capacitors. The leads are sleeved with insulation from 5KV test lead wire. The assembly is held in place by three longer screws with standoffs to limit clamping pressure.

The other mod is the delay circuit for relay RY302 which sequences the release of that relay to prevent arcing. No arcs have occured. (Thank you WQ9E!)

Here is a high-voltage switch under the chassis in the Viking Five Hundred. The lower pair of contacts had burned away. Thankfully, the rotor contact was un damaged. I’ve seen other Viking 500's in this condition, so it must be a fairly common occurrence. This section of the switch is made up of two completely separate sets of identical contacts that are actually wired in series with each other apparently to provide a wider gap to prevent arcing. Hot switching may have initiated the arc damage.

Here is the switch after making repairs. The replacement contacts were sourced from a donor Johnson Viking Ranger.

The repaired switch reinstalled.

I had paint mixed to match the E.F. Johnson Maroon. The Viking Five Hundred case needed repainting as does most of my Johnson Viking gear. Here it is just after painting. The front rim of the Johnson Viking case is intentionally left unpainted to make electrical contact with the front panel. This is necessary to assure a good, RF tight enclosure. This case is masked off at that location.

I brought the Viking Five Hundred home in January 2023. Here it is May 16, 2023, and the power supply top and bottom covers are finally back on.

Here is the finished Viking 500 in the shack.

Johnson Viking Five Hundred Startup:

I had been looking for a "500" since the late 1970's. After reading of the arcing and sparking complaints by owners over the years, it seemed it was a poor design. Thanks to Mike and Rodger from the Antique Radio forums, I made their suggested modifications to the 500 that would prevent this erratic behavior.

This transmitter had been stored in unfavorable conditions for many years; the rusted power supply chassis indicated moisture had been present. After many weeks of work on the 500, it was finally time to fire it up. Well, hopefully fire would not be involved! At first, the High Voltage fuses were left out, and it was energized only on the low voltage circuits. The filaments on the tubes lit up normally, the panel lamps came up, and the fan whirred along nicely. I ran it like this for several hours.

High Voltage testing: I’d never thrown the switch on a Viking 500 and didn’t know what to expect; the memory of users claiming arcs and sparks were unsettling. Re-installing the HV fuses, I hesitantly turned on the keyswitch. Immediately, a sharp snap and loud buzz accompanied the lighting of the 811A filaments—I quickly shut it down! The sound was from a relay in the power supply that was merely mis-aligned. The relay aligned, the next test started out fine—a smooth startup! Again, I let it cruise for an hour or so before keying up.

The first key up: After going through the manual and setting all controls for the band selected, I finally got the nerve to key this beast up. Gripping the D-104 microphone, a click resulted but no response from the transmitter—no high voltage! My heart sank; is this a bad high voltage transformer? Opening up the power supply, the HV transformer has continuity on the primary and secondary windings. Further tests showed no voltage is getting to the HV transformer primary. The culprit was the relay serving the HV transformer was not making contact. Some massaging of the contacts, and all is ready for testing again.

The second key up, we have high voltage! Now it was time to check to see if my worst fear would be realized: the condition of the modulation transformer. I keyed up and tuned up to 100 watts. Slowly turning up the audio control, I tested the microphone. We have audio. The modulation transformer is good!

Retuning, I found the transmitter will produce 300 watts of plate modulated AM. Testing on the air, it is a very smoothly operating transmitter and gets good audio reports.

This entire project has been worth every hour and dollar invested.

Modifications:

1. The infamous 18K "Chernobyl" resistor in the VFO has been changed to a 20K, 5 watt version. The original resistor is attached outside the VFO cage to show it was replaced.

2. The 6AU6 in the VFO was replaced with a 6AH6 as advised by WQ9E.

3. The two 866A mercury vapor rectifier tubes were replaced by a pair of 3B28 xenon gas rectifiers for safety reasons.

4. Inrush current limiters were installed on the 120 volt circuit and the 240 volt High Voltage transformer primary leads.

January 2025: Trying to check in to a nationwide AM event, the audio went sour; another station reported it sounded like "sideband". A good audio signal is present through the audio chain and at the secondary of the interstage transformer. Took the Viking 500 out of line and resorted to the old faithful Viking Valiant as the main AM transmitter.

July 2025: The 500 on the bench again: The 811A's test good. I swapped in a new modulation transformer and NOS 811A's at anything over 140 watts output, it seems to break into oscillation. The problem was with the DX Engineering balun. The conductor was arc welding into the toroid during keydown which caused the SWR spike and the audio problem. Taking the balun out of the feedline resulted in clean tune up and audio. Power on most bands is around 300 to 350 watts output at 305 mA cathode current. The power output of the Viking Valiant was low enough, so it did not induce the arcing condition; this is partly why I did not supect the balun early on.

The 5KW Balun arced and burned away part of the toroid.

August 1, 2025

The new balun is installed. Unable to contact another ham in the evening and unable to get into the SDR at Half Moon Bay, I connected to a SDR in Utah for testing. The signal was very strong, and the audio was better than I had hoped for.

Tips on Operation

For years, the Viking 500 was thought to be a skittish and problematic transmitter that arced and blew fuses constanty. The problem was largely due to residual energy in the tank circuit having nowhere to go upon un-keying. One of the relays in the power supply was designed with a residual magnetic field to delay unkeying until after the energy dissipated. A fix was discovered, so that unfotunate behavior can now be eliminated easily by adding a diode and small electrolytic capacitor. (Thank you WQ9E).

Once it is learned how to set it up, the 500 is a very nice and smoothly operating transmitter and solid performer. To be fair, abuse or lack of proper tuning may well break them! With careful tuning and loading per the manual along with judicious control of the audio while monitoring the signal with an oscilloscope, it will keep performing as EF Johnson intended. Many users have reported years of trouble-free operation.