Help with red plating VH4

[mansinmind]

Hello all,
I need some help with my vh4. I recently replaced some 5881 tubes in my diezel with some ruby 6l6 tubes i got about 6 years ago. after playing for about 30 minutes i start to get a hum and tubes start to red plate. yesterday was one set of tubes but today its the other set. this wasnt an issue ever with the 5881 tubes. did i have bad tubes sitting around the last 6 years? is there a way to diagnose the issue? i follow the tech manual to bias the amp (65mA) using the trimmer pot must it be done twice? ie, first with the red and yellow wires and then blue and red? much help appreciated!

 

[Ventura]

Hello all,
I need some help with my vh4. I recently replaced some 5881 tubes in my diezel with some ruby 6l6 tubes i got about 6 years ago. after playing for about 30 minutes i start to get a hum and tubes start to red plate. yesterday was one set of tubes but today its the other set. this wasnt an issue ever with the 5881 tubes. did i have bad tubes sitting around the last 6 years? is there a way to diagnose the issue? i follow the tech manual to bias the amp (65mA) using the trimmer pot must it be done twice? ie, first with the red and yellow wires and then blue and red? much help appreciated!

Did you flick the chassis switch to 6L6??
And 65mA is for PAIRS of tubes, not singular.

 

[mansinmind]

The chassis switch is to 6L6. Yes, the 65mA is per tube set. Im not biaising the amp to 130mA on the multimeter (65x2) Im adjusting the trimmer so that Im reading 65mA