Bias Problem Mullard EL34

[3 Mile Stone]

Okay, so when I got my RM50HB it had Ruby 6L6's in it. I checked the bias and adjusted it a tad to about 33 mV. I decided to try out some different tubes so I order a fist full from Tube Depot. First I put in the JJ6V6?s. They sound great and they bias just fine. Next I put in the EH6L6?s and they bias okay although they are a little off from each other about 2 or 3 mV difference from test point 1 to test point 2. Then I put in the Mullard EL34?s and boy, they are WAY OFF! I can barley keep it in range. When I put the red lead in test point one it?s at about 30 mV and then when I put it in test point 2 it?s at about 38 or 39 mV. Not exactly consistent or ideal. Is this normal to have one tube be so far out of range with the other? These were sold as matched pairs and when I cross check the tubes by putting the red lead in test point 2 and the black one in test point 1 it reads about 4 mV. Manual says anything over 5 is not a well matched set of tubes. Why are these tubes reading so far apart from each other?

Ideas or comments any one?

 

[3 Mile Stone]

Okay, I'll make one semi-embarrasing feable atempt to bump this probing question back into play. I figure if you guys are willing to give advice about casters surely you might could maybe throw me a bone and comment on whether this biasing thing is normal. :lol:

Anybody?

 

[MetalMajik]

Well, I'm no tube expert, but I'd say you either got a bad set of tubes or perhaps they were damaged durring shipping. Tubedepot.com and Tubestore.com both test their tubes pretty thuroughly and I believe they have a 90 day guarantee on all their tubes, so I'd try contacting them and see what they say.

That kind of bias is definatly not normal, nor is it acceptable

You might also try running the bias a little hotter and see what that does. I Think the bias range on an EL34 is 40-45 mV

 

[Scooter]

That's no matched pair.

 

[Viet_Hetzer]

That's pretty bad even if you don't get a "matched set."

 

[3 Mile Stone]

Okay. That was the first time I've done any biasing and I thought it was strange. BACK they go. Even though they biased poorly I liked the sound of the Mullard EL34 maybe a little over the 6L6's.

Thanks fro the replies,