Plate Voltage Fluctuating

[stokes]

Retubing a 5E8 Twin clone for somebody,check the plate current on the old tubes and see 372vdc-57ma.Got sidetracked and when I got back to it an hour later I check again and I am seeing 410vdc with 64ma,6L6GC tubes by the way.Investigating further I see that most times on power up the plate current and volts start high and slowly drop about 50-75 volts.At times on power up it will just read steady,sometimes as low as 345 or so and as high as 430v,but most times I get the high to low drift. Checked for shorts with a light bulb in series and also a volt/wattmeter and it doesnt have any shorts.Tried the new tubes and I get the same fluctuations.The silver flashing on the old tubes is turning brown,so I assume they were redplating when it was running at the higher volt/amps.I am thinking it is a problem with the bias supply and will check that,but wanted to see if anybody here has any ideas.Thanks.

[stokes]

It was a bad rectifier tube.