dual triode issues

[ALBATROS1234]

i have a scenario that happened in the last day to 2 different dual triodes. on the first i am modding a r2r for my neighbor into a champ circuit. normally when i fire it up i am good to go. this time it lit up but wouldnt make sound. i traced the wiring to see if i made a mistake it was fine. so i start testing voltages, power tube is fine but when i get to the 12ad7(basicallt a japanese 12ax7) one triode was normal range and the other was reading really high like there was no voltage drop one plate said 110vdc and the other was at 304vdc on the plate and 312 on the other side of the 250k plate resistor. i swapped the tube and voila it worked.

so today i get a pair of nos reflektor 6SL7s which are 6H9C, one worked fine and the other was dead. i take  out the meter and same scenario one plate is normal voltage and the other its seemed like the dropping resistor on the plate was not doing its job. so i am wondering what has happened. deductive reasoning makes me think there is something wrong with the cathode, perhaps shorted , so that the cathode resistors are not doing there job of biasing hence not voltage drop. but i am only making an assumption and i wonder is this the case or could it be something else. anyone else ever see this before. really odd that i have never seen this and within 24 hours same prob 2 different tubes.thanks gents

[sluckey]

I think it's just a coincidence.

[ALBATROS1234]

sure but i just found it funny and felt like sharing.lol.

is that what it is a shorted cathode that would produce this symptom? thats really why i posted ,was wondering what caused this.

[sluckey]

Shorted to what?

[ALBATROS1234]

the heater i am supposing? my thought were that triode ( half of the dual triode tube) wasnt biasing properly. so the voltage wasnt dropping on the plate. for instance on plate 1 i had say 125vdc. on the other side of the 250k plate resistor i had 312vdc. on plate 2 i had like 304v after it passed through an identical 250k resistor from a 312v source split in 2 to feed said plates. i assumed the cathode for whatever reason wasnt able to cause the voltage drop even though the components on the cathode were tested good. unless my concept of how bias in a dual triode occurs. you raise the value of the cathode resistor and you get a smaller drop on the anode.