500 #2 Power Supply Project - RT's Radio Home Page

Background:

The EF Johnson Viking Five Hundred AM/CW transmitter was manufactured as a set of two major components, the Desktop RF Deck and the remote Power Supply/Modulator unit. These two units being connected together by plug-in umbilical cables. The separate units were necessary since power supply itself weighs around 120 pounds, while the RF deck weighs around 65 pounds.

What happened to the power supplies?

Manufacture of the Viking Five Hundred ended in 1964. AM operation had long been subject to annoying heterodyne interference by other stations on nearby frequencies, so during the 1960's, it was gradually superseded by Single Sideband (SSB) operation. The old heavy, wideband AM transmitters fell out of favor and were often relegated to the garage, other storage area or in sheds. When the owner passes away, the family members are completely unaware that the big, heavy unmarked power supply "box" is a necessary component serving the Viking Five Hundred RF deck, so many of these were sold off separately or sadly, went to the landfill.

The AM transmission mode never disappeared completely from the amateur radio scene. Today, there are dedicated hams who still see value in the AM mode and enjoy operating these classic rigs.

The New Power Supply:

The "Viking 500 #2" RF deck detailed elsewhere on this site was separated from its power supply at some point in history. The RF deck is now operational, so the construction of the new power supply/modulator unit is underway and is detailed here.

A Viking Invader power supply chassis was initially intended as the base for the new power supply; however, extensive modifications would have been required.

A brand new chassis:

Chuck Hurley, K1TLI reached out to hams who needed a new power supply chassis for orphaned 500 RF Decks. I committed to buy if he could produce them at a reasonable cost. Several other hams committed, and after a few months Chuck came through with a nice product.

The layout must have taken considerable time and effort. The machine work on the chassis is clean, and the nickel plating is well done. The original Johnson chassis was polished to a mirror finish prior to plating; this new chassis was not. Polishing would have likely added significant labor cost to the chassis, so it was best to skip that feature. A few more Viking Five Hundreds may have been saved due to the making of these new chassis; thank you Chuck!

Chuck Hurley does very nice work; here is a link to his website: https://johnsonradioresto.com/home-page

Another view of the new chassis.

Progress Photo:

The photo shows the major components mounted on the chassis to verify mounting of newer style components, such as relays to verify no conflicts in placement. Wiring has been started; however, a new transformer ordered from Hammond has been delayed for a few weeks. The plan is to have the unit completed and ready for testing in March 2026.

I only use good capacitors in my builds. The Viking Five Hundred is a special transmitter, so it deserves higher quality components. The high voltage side of the power supply is fitted with Japanese Rubycon 100uf, 450VDC, 12000 hour radial-leaded electrolytics. These are better than the best axial electrolytic capacitors I found. They were $2.25 each when buying in lots of 10 or more.

Power Supply Modifications:

1. The two 866A mercury vapor rectifier tubes were replaced by a pair of 3B28 xenon gas rectifiers for safety reasons. The 866A's can arc if improperly warmed up, and this arc can damage the high voltage power transformer.

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

3. A 10uf@350VDC electrolytic capacitor and 1N4007 isloation diode was employed to delay unkeying of the 4PDT relay R302. (WQ9E modification.)

4. Added safety: As shown in the original schematic, relay RY301's contacts are directly connected to the 240 Volt AC mains. For an additional layer of safety, a double 3AG, 10 Amp fuse holder with fuses is installed underside of the chassis between the 240 Volt mains and the contacts of RY301.