Studdering mercury vapor diodes

[Demonkleaner]

I have one 866AX brighter on one end of the HV winding. It's always on the same winding no matter the tube I use. I assume I have more current draw due to unbalanced windings on the HV transformer (Antek toroid). I need to do some checking I suppose.

 

[baudouin0]

I wonder if they flicker if the electrolytics have lost their capacitance.

 

[WntrMute2]

Probably not the cause in my case. These caps are brand new film Panasonic caps.
EZP-V60107MTC Panasonic | Mouser
Less than 100 hours on the breadboarded project. But maybe.

 

[rmb]

My heater voltage to the 866ax tubes is a little high at 2.77V. I'll drop it down in the final build.

2.77 volts on the filament of a 866AX is WAY too high. That is almost 11 percent over. Too much vaporized mercury in those tubes can lower the PIV and/or overheat the heat shielded filament and shorten tube life. The rated filament voltage (at the socket) for a 866AX is 2.50 volts, and the max filament voltage is 2.62 volts. Does the rectifier filament transformer have primary voltage taps? If so, set the tap for a higher primary voltage or add some resistance to the primary side to get that filament voltage down.

The filament voltage is critical with mercury vapor rectifiers regardless of whether one is dealing with a few hundred volts to a kilovolt or so with audio, or with kilovolts with radio transmitters.

 

[WntrMute2]

Can I add resistance to the secondary side of that transformer instead? I'm thinking no as the resistors would have to handle the rectified B+.

 

[rmb]

Wouldn't recommend adding resistance on the secondary side of the filament transformer...a pair of 866AX tubes draws 2.5 volts at 10 amperes parallel connected. If you add wire for resistance from the secondary to the rectifiers, it is at HT. Changing a primary tap (if available) or adding a small resistance on the primary makes more sense. Transformer probably draws no more than 30 watts off AC mains including iron losses....