So I just played with the bias on my 6505+

[Mephis]

I got bored of messing with my kramer's action and decided to play with my amp, since it's infinitly more fun to mess with amps.

The bias pot was set to dead 0. (Now don't be worried, the sweep on the pot is next to nothing, max in either direction can't hurt anything, at least from what Bob at eurotubes told me.)

It sounded cold and the rythm channel was getting to much crossover distortion to even get a clean tone at low volume.

I bumped it up 1/4 turn.

The rythm channel was getting cleaner and picked up a little jangle to it. Distortion was still a little cold.

Bumped it up to about 2o'clock.

Tubes are now looking healthier, less blue haze on the tubes. Cleans are actually clean with a good bit of jangle and twang. Lead channel is now picking up more dynamics. It's also slightly cleaner.

Maxed the bias out.

Tubes look even healthier. No blue haze at all anywhere. Cleans seem about as clean as they're gona get. Crunch channel now sounds usable instead of muddy cold sludge. Lead channel now sounds nice and warm, dynamics are great, EQ is now far more usable. No more turning the highs down to 2.


Funny how much difference a tiney bias adjustment can make... Everyone says the pot has very little sweep, but it seemed like a pretty massive tonal difference to me.

 

[I_M_Ken]

Re: So I just played with the bias on my 6505+

is it safe to just adjust the bias like that?
im afraid i might screw up my amp. thats why i never touched the bias "screw" like thing.

 

[Mephis]

Re: So I just played with the bias on my 6505+

On that amp you very well can mess it up.

This amp, you really can't unless you've had it bias modded.

Don't screw with it until you talk to a professional and get their opinion.

 

[I_M_Ken]

Re: So I just played with the bias on my 6505+

ahh, ok, got it! heh... well blue voodoos are super rare in singapore. i guess i could be the only person that has one of those early 90s BV combo amps here. so i'll stay away from tweaking it and let the right ppl play with it then.

 

[Stratman]

Re: So I just played with the bias on my 6505+

I use to have a 60 Watt Blue Voodoo.

I never believed the forum complaints concerning about this amp.

Sweet little (But not light) combo.

Singapore - Do you play out?

 

[wixedmords]

Re: So I just played with the bias on my 6505+

It is much better to be observing what the bias is doing in this process, but changing your bias within the proper range is another modding technique. You can run it hotter which usually gives it more snap, more clarity, or colder which can be a bit darker, a bit less articulate.

 

[Virtual Kevorkian]

Re: So I just played with the bias on my 6505+

Sorry dude, you're still not getting it out of crossover distortion. You need another 2-3 full 360º turns on that bias pot to do that.

And if you think the crunch channel sounded like muddy, cold sludge, you need your ears checked. All it is is a darker version of the lead channel with less gain and a tighter low end. I actually use that channel the most.

 

[Mephis]

Re: So I just played with the bias on my 6505+

I know I'm not getting it out of cross over distortion, I don't really want to because that would kind of lose the 5150 tone.

I just wanted to warm up the bias some to see what it would do, and it was a big improvement. Probably sounds more like a regular 5150 now instead of a 5150II.

 

[Gearjoneser]

Re: So I just played with the bias on my 6505+

Is that one difference between the 5150 and the 6505?....the addition of a bias pot?

I think people shouldn't be afraid of messing with the bias on their amps, as long as they don't turn the gray plates inside the tube orange/red. If that happens, immediately shut off the amp, and turn the bias back toward where it was.

Even though I've biased amps by ear before, it's a better idea to have a Bias Tool socket, a volt/mA meter, and then do it by ear but staying in the normal operating range of the tube. You're less likely to make any mistakes that way. Still, it's not rocket science. You're just setting the idle of the amp, the way you would with a car, so it runs it's best.

 

[Virtual Kevorkian]

Re: So I just played with the bias on my 6505+

The other difference is an added preamp tube for extra gain, they're also biased colder.

Well that and the bias pot.

Wrong... that's the difference between the 5150/6505 and 5150II/6505+


THERE IS ABSOLUTELY NO DIFFERENCE BETWEEN THE 5150 AND 6505. End of story.

 

[Mephis]

Re: So I just played with the bias on my 6505+

Whoops, read his post wrong...

 

[Scott_F]

Re: So I just played with the bias on my 6505+

Hmmm.....

Danger, danger Will Robinson.

I'd be highly suspect of adjusting bias totally by ear. Depending on how the pot is made, a little sweep could be a HUGE range.

 

[krankguitarist]

Re: So I just played with the bias on my 6505+

Hmmm.....

Danger, danger Will Robinson.

I'd be highly suspect of adjusting bias totally by ear. Depending on how the pot is made, a little sweep could be a HUGE range.

From what I hear, the bias pot on the 5150II/6505+ has a pretty tiny range. Though, I agree, It'd be much better to actually check out where the bias is at, just to make sure that you're running it in a "healthy" way.

 

[Mephis]

Re: So I just played with the bias on my 6505+

Hmmm.....

Danger, danger Will Robinson.

I'd be highly suspect of adjusting bias totally by ear. Depending on how the pot is made, a little sweep could be a HUGE range.

That's why I talked to Bob at eurotubes for awhile.

He told me the sweep is very little. If I'm remembering right he said the resistor on the pot is 12k and to give the pot a more regular range you would have to put in a 6.8k resistor.

Now all that might as well be greek to me. But maybe you would understand that?

Plus it mainly just picked up clean headroom and smoothed out the gain. Wouldn't biasing to hot kill your clean headroom?

 

[Gearjoneser]

Re: So I just played with the bias on my 6505+

I don't know as much as Scott does about the technical aspect of it, but in my experience, you can't really harm your amp unless it's biased hot enough to start turning the plates orange/red. If you start seeing that, you're beginning to ruin your power tubes. If not, you're probably fine, as long as the amp sounds really good to you.

 

[I_M_Ken]

Re: So I just played with the bias on my 6505+

I never believed the forum complaints concerning about this amp.

Sweet little (But not light) combo.

Singapore - Do you play out?

No dude, i dont play out. its too heavy to lug around especially since i dont have a car. really really heavy. So it stays only at home for now.

why did you get rid of it? its damn rare in singapore man.