7JP4 Heater protection in series string sets

[jr_tech]

Of course, installing a 6.3 volt transformer to power the 7JP4 heater would provide the most constant source of voltage, but other schemes have been mentioned here.

One scheme places a surge suppressor diode accross the heater source to limit the high voltage surge during turn on of the set (sometimes as much as 12 volts). The part number mentioned is P6KE8.2CA... is this correct and still thought to provide good protection? I can order some on the 'bay.

Other schemes??

For grins, last night I experimented with two banks of ten series-connected 1n4005 diodes, which limit the heater voltage to about 6.4 volts at 600 ma heater current, but at the high turn on surge current allow a momentary heater voltage of nearly 10 volts!

jr