Intermittent High Voltage Arcs are common in transmitters of this era.

The Viking 2 sockets for the 5R4 rectifiers have rivets. The sockets are not spaced far enough from the chassis. The easiest fix is to replace the mounting hardware with insulated standoffs and longer screws to increase the path. Corona dope (from GC) also helps in addition to this fix if used to cover carbonized areas on the socket and rivet, but do not depend on it alone. I heard that tool handle dip also can be used, and is available at good hardware stores. Change the hardware to increase the spacing. Also sleeving may be necessary on the HV filter choke leads all the way back into the bells of the choke enclosure. This sort of thing can cause problems in the DX100 high voltage circuitry.

Click on thumbnail to see sleeving indicated by arrows. The circles call attention to the ceramic standoffs. The VR tube dropping resistor is circled to show where it has been moved to provide better mechanical stability.

Valiant One and 2 also have problems. Inspect carefully for any arc points in the radio before doing any mods.

I include photos of arcing on the terminal strip for the filaments of the 866. Also, the wiring for the HV plate filter choke are insulated with additional sleeving. The damaged terminal strip had to be replaced with ceramic standoffs. The chassis shows carbonized areas due to a long time problem with this that was not addressed by the previous owner. This was a persistent intermittent that was hard to track down the first time.

Click on thumbnail to enlarge.

There is another terminal strip near the LV fuse for the 866 filaments which can cause trouble.

Click on thumbnail to enlarge.

Sleeving may be required on the 2.5 VAC filament wires into the LV transformer. The 4 pin sockets may arc. They are often phenolic, not ceramic. The jumpers for the filaments between the 866 sockets can be unbundled from the wiring harness and replaced with wire having better insulation. Or switch to Silicon Alley rectifiers and eliminate all 2.5 Volt filament wiring if the insulation in the transformer has already failed. It could save you having to replace a transformer.

Replace the 866s with 3B28 tubes to avoid mercury warm up issues with resulting flash over upon application of HV power. I have commercial solid state replacements in my rig. You may find the Silicon Alley units work for you. I like to use a solid state relay to key up the high voltage transformer primary, which switches the AC at zero crossing. This prevents transients which can flash things over or damage solid state replacements; it also prevents a scary thump when you press the PTT switch.

The modulator transformer terminal strip is a possible problem. Ceramic standoffs help.

Click on thumbnail to enlarge and note the purple circle around the added standoff to correct arcing of the plate lead of the modulator.

The back panel jumper connector J8 is a possible problem. So is anything with modulated B+ on it. Keep this in mind if you want to go to +130% modulation peaks and clip just the negative side to reduce splatter.

The photos included with this small article are self explanatory, and a grim record of the battles I have had with this problem.

All these potential problems are the reason I did not attempt the “East Coast” mods that raise the HV B+ to 1000 V on the modulator. Some people have had success with this approach, but looking at the wiring harness and all these known failure points, I sought another solution. This one worked out OK for me. Look it over, and see if it will work for you. A new $25 driver transformer goes a long way toward improved performance. This one makes full modulation and decent frequency response without exceeding ICAS tube ratings or risking failure of old wiring to “hot rodding” the HV power supply.

Everyone has their own solution; just because they differ does not mean that one or more of the approaches is wrong. I present my reasoning here, and the alternatives to my approach; you are free to explore options. I hope you found something useful.