Ok, swapped the tubes...now a bias question

[madDdog67]

Ok, I went ahead and swapped the 6L6s out for the EL34s in my RM50. I checked the bias before I swapped the tubes, and the 6L6s were within range. When I checked it after I put the EL34s, in was pretty low, like 20mv. I turned the bias knob a *hair*, and it shot up to over 60 :shock: so I quickly turned it down. To make a long story short, the bias went nuts anytime I tried to nudge it over 28ish mv. Once I get it that high, if I even LOOK at the bias adjustment, it just shoots up.

Any ideas on what the problem might be? I suppose I could run it cold, that won't hurt anything as far as I know (which is very little about this to be honest).

 

[wesarvin]

I would like some help on this issue as well...

And only ONE of my bias pots work!

 

[eyeball987]

Could be a bad tube. That was the reason for the only bias issue I have had.

 

[Jaded Faith]

Sound like a broken bias pot in both of your amps. They can be damaged if you are too rough with them and I have seen it before. Try a different set of tubes (the originals are fine) if you you haven't already to rule that out first.

 

[madDdog67]

I'm gonna pop the stock tubes back in and check to see if the bias adjustment still acts wacky. Could be adjustment pot is bad or not working right.

 

[wesarvin]

Sound like a broken bias pot in both of your amps. They can be damaged if you are too rough with them and I have seen it before. Try a different set of tubes (the originals are fine) if you you haven't already to rule that out first.

That's what I was thinking. I think the head was whacked during shipping a couple of times, as the reverb tank also had a screw missing.

When I pulled the chassis to have a look at things, the bias pot was a little bent. I gently bent it back, but the bias is still pretty touchy and also only one test point works. It acts the same for both sets of tubes that I tried.

 

[wesarvin]

Sound like a broken bias pot in both of your amps. They can be damaged if you are too rough with them and I have seen it before. Try a different set of tubes (the originals are fine) if you you haven't already to rule that out first.

That's what I was thinking. I think the head was whacked during shipping a couple of times, as the reverb tank also had a screw missing.

When I pulled the chassis to have a look at things, the bias pot was a little bent. I gently bent it back, but the bias is still pretty touchy and also only one test point works. It acts the same for both sets of tubes that I tried.