el-34 problem with my mkIII

[geoangus]

I've had the amp a little over a year (1989 imbuya blue stripe simulclass), and have always had the two sets of 6L6's duets that were in it when I bought it. I like the 6L6 sound, but thought I'd try EL-34s (MESA STR447s) in the outer sockets. I run the amp solely in class A mode.

The first set of STR447s sounded "squelched and scratchy"; the volume would "drop out" . Actually, I don't think it ever dropped in. Sounded like it was underwater or something. Just awful! Thinking maybe they were bad tubes, I exchanged them at the local shop. Well, second set just as bad. I pop the 6L6's back in, all is well.

What gives??? Like I said, I prefer 6L6's anyways, but now I'm wondering if something is wrong with the amp.

thanks

 

[Boogiebabies]

It's possible that the EL34's are running so hot, or biased so high that they are going into cutoff. What color code are they ?

 

[geoangus]

I don't have them in front of me (I'm at work), but I'm pretty certain that they are yellow. I thought the code was just a cross to groove tube. Are there certain Mesa tubes that are NG to use with MkIII? If yellow is no good, what color would be okay?

thanks - learning a little everyday

 

[geoangus]

no luck reaching M/B - lots of voice messaging, NO REPLY

any risk of damage if I just stick with 6L6's??? Amp sounds great; I was just experimenting when I discovered this issue.

thanks

 

[Schmoog]

you probably wont damage the amp. but it sounds like a bias cap problem. check your tubes (the el34's) for red plating. if they are red plating, then your bias cap is shot probably

 

[Shep]

i use Ca7 EL34 in mine and they sound Realy good..