[R-390] B+ Dropping Resistance (was Drill a Hole...)

[K2CBY@aol.com]

Perhaps this is heretical but I saw little point in retaining the tube sockets on the PS chassis once the rectifiers had been replaced with solid state diodes. I yanked the sockets and plated over the holes with 16 ga. aluminum. I mounted the rectifiers on the underside of the chassis and a dropping resistor on the top side where it can get some air. (Putting the resistor on the PS chassis also eliminates the need to use a "special" audio chassis, so audio units can be freely swapped.)

The VFO and BFO shouldn't chirp no matter what, since they derive regulated B+ from the VR tube mounted on the audio chassis. The only way a dropping resistor in the unregulated line could affect this is if it lowers the regulator supply side voltage to the point where the gas tube loses ignition.

The only thing that bothers me about the solid state rectifier conversion is that B+ comes on full blast almost instantaneously. It takes 30 to 40 seconds for the filaments to heat up enough for the tubes to draw current through the dropping resistor and lower the B+ bus voltage. Putting an inrush protestion thermisor in series with the AC line helps but doesn't cure the problem.

For essentially the same reason, I favor replacing the ballast tube with a 12-volt tube having a controlled heater warm-up time (in my case a 12BY7 from an old Tektronix scope) rather than a fixed resistor.