Jim,
Thanks for the explanation.? I understand the principle of what you are describing, eg the energy in the tank circuit causes the voltage to rise on the anode on the positive cycle, before dropping down on the negative cycle of the RF.? With these Russian tubes having such variability as you described, i guess its safer staying with a lower plate voltage and keeping the swing lower.? I don't have the equipment to hi pot test the tubes, but was planning on following the instructions on the internet around "reactivation" of the tube.? Detail copied in below
To avoid flashover in a new or a long time unused tube, it is prudent to prepare ("reactivate") it for his task. There are various opinions and solutions how to do it, but with a GU-43 it can be relatively simple. A DC of 10 to 15 V is sufficient for the tube to draw 900 mA as the grids are connected to the anode. Heat the tube 30 minutes with a filament voltage of 12.6 V. Then supply a "high voltage" of about 15 V and set the voltage to a current of 900 mA. If possible use a current limiter, because during reactivate the current can increase suddenly so that continue monitoring could be necessary to maintain 900 mA. Usually I will not reactivate longer than an hour or so. Soon you will find out at which voltage a good tube drawn 900 mA (or 800 mA/12-12.5 V) so you have an indication if another tube is better or not.
