A few things to note:
The EH's seemed to draw about 10 more volts of plate voltage than the JJ's. Also, I was barely able to get the JJ's biased in spec. I had to turn my bias pot all the way down to get them in, and then it was just barely. I checked my voltage on pin 5, and I am able to go from -44v up to about
-31v. This remained consistent with both tube brands, but using the cathode resistor method of biasing, I was getting about 20ma with the pot all the way down with the EH's, but about 36ma with the JJ's. Just barely enough to get it biased.
Also, I noticed that the redplating didn't seem to occur with the JJ's until they had been played for about an hour after they were first installed. After that first hour break-in though, they redplated almost immediately after you started playing, even if you left the amp off for several hours. I am assuming the EH's were the same way, although I didn't notice them until after they had been installed for a few days(more explained on this later).Also, all the voltages, including plate, seemed to drift up after you play and then let the amp sit for a while. What I mean is, you can fire it up, check the voltages, bias it, and play it a bit. Then turn it off, come back a couple hours later, fire it up, and check the voltages again, and they are all higher. I expect a little drift when breaking in new tubes, but the EH's are fairly broken in by now, and they still do it.
One last thing of note is that I did put in a new PT that puts out about 95 more plate volts than my old one. The new one is about 475v and the old one was about 380. The 475 was the reading I got when I first installed the PT. Now the EH tubes are reading about 495 plate volatge. Like I said, that's about 10 higher than the JJ's, whcih started at about 472 and drifted up to about 480 after an hour or so. But actually, I was noticing similar drifting behavior even with the stock PT. I put the EH's in about a week before I got the new PT. The first read was about 380, but after a couple days, they were reading about 390. Then like I said, they did a similar thing with the new PT, although you'd think they'd be broken in by now. Or maybe there is something else in the amp that is causing this and the redplating?
Anyway, I never noticed redplating with the old PT, but I'll be honest. I just got the amp in June and this is my first experience with amp biasing, so I may just not have looked hard enough. Also, the EH's were the first new tubes I had put on since I got it, and like I said I just put them on about a week before I got the new PT. They may have been doing it with the old PT, and I just didn't see it. I'm just trying to throw out everything here so I can get to the bottom of this and enjoy my amp again. I didn't change any board components when I put the new PT in, maybe I was supposed to?
Sorry for the long post, I just want to get all the details out so folks with more experience can maybe tell me what to do. Thanks for your help.
Here is what I did. After I read your post, I got the amp out, it was still setup the same as I had it the last time I was checking the tubes. It had the EH tubes in it as I had put them back in to check if the resistor change would work. I had biased it up using the cathode rstr. method, and like I said, I left the sttings as they were. Here are the readings I got using the shunt method.
