Bias Concern

[Ampoholic]

Howdy

I put SED winged C tubes in my amp, EL34s outside and 6L6s inside. Sounds great! The concern is the 6L6s. Two of the 3 I have won't bias any lower than .034. I understand this is inside the range, but I was wondering if this was an indication of anything, amp issue, tube issue, etc.

Thanks for looking!

BTW, I'm listening to NEW AiC on the radio! It's about time! Pretty cool, the singer sounds ALOT like Lane.

 

[nixerx]

im 90% sure your amp is fine.

 

[surreal]

hey sorry to hijack , but i have a similar question.
When mixing Valves in the Head , should they all be biased at the same level.
I mean if you have 2 x EL34's and 2 x 6L6's or KT88's should they all be running at the same Mv's.
Even though some valves need to run hotter or cooler than others.

Can the inside and outside pairs be biased at different Mv's ???

 

[Julia]

Tubes run best in the middle of their range. If you underbias a tube it will sound like crap. If you overbias it it will not last very long.

 

[Ampoholic]

hey sorry to hijack , but i have a similar question.
When mixing Valves in the Head , should they all be biased at the same level.
I mean if you have 2 x EL34's and 2 x 6L6's or KT88's should they all be running at the same Mv's.
Even though some valves need to run hotter or cooler than others.

Can the inside and outside pairs be biased at different Mv's ???

I've heard of many running mixed tubes with the bias set for the tube types. I'm been doing it without issue, just changed to SED EL34s.

Tubes run best in the middle of their range. If you underbias a tube it will sound like crap. If you overbias it it will not last very long.

Yeah, I kinda decided the middle was a good spot myself, just wondering if it's an indication the tubes may be going out since the bias pot is set as low as it can go and only gets to .034. Is it something to watch to see if the value goes up? Is it not a problem, don't worry about it? Some tubes are just like that?

 

[Julia]

How long have you had the tubes?

* Have a backup quad on hand.
* Have some 400 mA fast-blo little fuses on hand.

* might want to take the front panel off your amp so you can see the power tubes while you're playing. If the plates even start to glow you need new ones.

* if a tube fails, replace the fuse, and throw an older working tube in the slot. Turn on the amp, do not play but watch it for 20 minutes. If nothing goes funny (like the tube redplates) you can replace the quad. If the tube redplates, it's amp tech time because you may have a bad screen grid.