#1
I have an original run peavey 5150 combo. I'm told it's fixed bias. Does that mean I can toss ANY 6L6GC and ANY 12AX7 in it and not have problems as long as they aren't crappy valves?

thanks in advance
#2
The majority of production amps are "fixed bias." What this means is that the bias point is "fixed" external to the tubes. Most amps have a trim pot that makes the "fixed" point adjustable. Others, like Mesa amps, use a resistor to permanently set the "fixed" point. The other bias method for a tube amp is using a cathode bias, where eat tube sets it's own bias point. This is the case with true class A amplifiers.


I found this on another forum.
#3
Yeah, I read through all that I just want to make sure that I can literally put any 6L6GC or 12AX7 in this thing with no problems.
#4
Now I'm not an expert on tubes so you should see what other people say too but I think you can. From everything I've read you can put any brand in there as long as it's the right tube. You might a better brand then say a chinese but still anything will work just get the right model tubes in there.
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#5
My amp has a set bias switch for El34 or 6l6. From my understanding its the factory set bias for these tubes.Many people including myself find the factory bias to be a bit cold. I used the trim pot to adjust the bias to a bit warmer setting. This may be the same case with the 5150. But you should be able to put any tube of the same type in there. Even if its a different brand.
Gear:
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  • Gibson Les Paul Studio
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#6
Quote by Maggot3000
My amp has a set bias switch for El34 or 6l6. From my understanding its the factory set bias for these tubes.Many people including myself find the factory bias to be a bit cold. I used the trim pot to adjust the bias to a bit warmer setting. This may be the same case with the 5150. But you should be able to put any tube of the same type in there. Even if its a different brand.


+1

Just make sure your tubes glow orange/amber, OP.

If you're not switching tube types, it shouldnt be a problem, but check the color in case.

Blue is not ideal, Orange/amber is great, Red is BAD!!
Gear:
Ibanez RG4EXFM1
Peavey 5150II All Tube 120w Head
Avatar contemporary 2x12 (Celestion v30's)
Peavey Vypyr 15w (Fantastic Practice Amp!!!)

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#10
Quote by DakoRob
+1

Just make sure your tubes glow orange/amber, OP.

If you're not switching tube types, it shouldnt be a problem, but check the color in case.

Blue is not ideal, Orange/amber is great, Red is BAD!!


No. There have been a number of threads about this. Random tubes just glow blue, there is nothing wrong with it, and in fact a lot of people go to the trouble of finding tubes that will do this.

The 5150 combo is cathode biased. You do not NEED to change anything, though a lot of people mod the amp to get that additional control over it.

The Eurotubes retube packs are fantastic, they do a good job matching tubes up. I've used their regular 5150 212 pack before with great results.