Get Your Amp Biased

[The Golden Boy]

A friend of mine owns a electronics repair store. He's been bugging me to bring in my amps and get them tweaked right. Last week he was kind enough to hit my Park. I haven't had this amp biased since I got it 6-7 years ago. Although I've always preferred my Marshall, I've been pretty happy with the way the amp sounded- especially since a preamp tube switch a few years ago. After getting the amp serviced- good golly, this thing has tons more bottom end and it seems to have more "shimmer" to it. I had no idea how out of whack this thing was and I'm really glad I had it done!

Do it.

 

[shredaholic]

Re: Get Your Amp Biased

Is that all that was done, the bias? Seems a bit strange that you'd notice that much improvement from getting it biased again; if it was biased correctly in the first place it shouldn't have drifted out or sounded any different to how it was now.

 

[Scott_F]

Re: Get Your Amp Biased

Good advice. I take it for granted that people own tube amps, change out power tubes, but don't bias? WTF, mate?

 

[Zhangliqun]

Re: Get Your Amp Biased

Depends on how old the tubes are. Did the guy put in new tubes? If so, then a lack of bottom and punch might have meant the old tubes were about to go.

If the tubes weren't replaced, the bias might have been set a little on the cold side or drifted that way over time.

 

[Scott_F]

Re: Get Your Amp Biased

Is that all that was done, the bias? Seems a bit strange that you'd notice that much improvement from getting it biased again; if it was biased correctly in the first place it shouldn't have drifted out or sounded any different to how it was now.

Tubes drift over time, might have just gotten way off. Even when you get a new pair of power tubes, you ought to rebias after a month or two of play time. They really do often drift that much in such a short time.

 

[the guy who invented fire]

Re: Get Your Amp Biased

Is that all that was done, the bias? Seems a bit strange that you'd notice that much improvement from getting it biased again; if it was biased correctly in the first place it shouldn't have drifted out or sounded any different to how it was now.

Having an amp biased can make a HUGE difference if it off...if the tubes get changed the bias needs to be set...period!

 

[The Golden Boy]

Re: Get Your Amp Biased

New tubes were put in when I got it and it was biased then. I've switched tubes a few times usually the Teslas and a new matched set of EHs.

 

[shredaholic]

Re: Get Your Amp Biased

Having an amp biased can make a HUGE difference if it off...if the tubes get changed the bias needs to be set...period!

Unless it's cathode biased


I know tubes tend to drift out of bias in the first few weeks or months of use - especially modern production tubes, but I've never known tubes to drift out of bias over a period of years unless the tubes are getting pretty worn. I've never really put it to the test though, as I'm always rebiasing after doing some mod or another.

I've actually installed external bias meter jacks and a pot for each tube on the outside of the chassis, so I can always monitor bias on the fly and if necessary change it - plus you can match tubes to each other even if they aren't a matched quad. I'd say that all amps should have this feature, but there's always gonna be some kid at GC that goes round the back of amps and turns them all up to 100% plate dissipation :laugh2:

This was during installation (hence only 2 / 5 jacks installed so far here), it'd only cost you about $5 in parts and takes about 30 minutes to install. I highly recommend it to you guys - even if you get a tech to install it. It means all you do is get a DMM and you can easily and safely bias your amp yourself, and never have to pay for matched tubes again!

 

[shredaholic]

Re: Get Your Amp Biased

New tubes were put in when I got it and it was biased then. I've switched tubes a few times usually the Teslas and a new matched set of EHs.

You mean you didn't rebias after putting Teslas and EH Power Tubes in? That would explain the stray bias if so, not natural drifting. If you're referring to preamp tubes, there's no way whatsover that they could've affected the bias so I wouldn't worry about changing preamp tubes whenever you want.

 

[wixedmords]

Re: Get Your Amp Biased

Quite impressive with the seperate bias pots Shred. Seperate bias pots would allow you bias each power tube individually, therefore allowing you to overcome the difference in a set of tubes, even a "matched" set. Nice.

An amp will sound different at 50% dissapation than it will at 70% dissapation. I use it as a mod technique. Think of it, you could have (2) of the same amps, and biasing them at the 2 numbers above would give you (2) amps that sound a "little different".

No cost.

 

[Nite_Maresz_25]

Re: Get Your Amp Biased

My Mesa has a fixed bias, and It's a great feature(the wallet likes it too!).

 

[kmcguitars]

Re: Get Your Amp Biased

I had a old pair of RCA gray plate 6L6's sitting in my parts draw for so long I don't even rememeber where I got em'? When I 1st got my HRD ( Just for poops & giggles) I put em' in... They sounded GREAT!! Good thing I checked my Bias... Them Sucker's where drawing 90mV with the trim pot all the way to the left? Moral of the story... If i didn't check my Bias, Them Tubes would have sucked the life outta my Amp.:smack:

 

[Dr.Mavashi]

Re: Get Your Amp Biased

Can anybody recomend somebody in San Francisco, who knows how to do bias right with other maintnance when changing tubes on Laney AOR 50??? THank you.

 

[LesStrat]

Re: Get Your Amp Biased

Oh, great. Now I have ANOTHER new skill to develop. When do the lessons begin?

 

[flank]

Re: Get Your Amp Biased

When i took my amp to David Allen, he explained alot about the bias and mentioned how much it can affect the sound of an amp, along with a regular check up. Its all gradual so it might not be apparent, but the components can drift more and more "out of tune" with eachother, and the amp sounds less dynamic. I could definately hear how much more alive my amp sounded after he went over it, replaced any old components with drifted values, and biased it correctly. Much more dynamic sound when all the components were correctly alligned.

 

[kmcguitars]

Re: Get Your Amp Biased

Those BF Fenders aren't that easy to bias I hear.

Not In particular. As long as the amp has a bias trim pot, And you have the know how.
Fender really made it easy with the Hot Rod series, By supplying a Bias point on the PCB. All you need is a Multi meter-proper screwdriver- alligator clips and a Healthy dose of COMMON SENSE! (i.e.) (The abiltiy to follow simple Instructions). But I'm sure many have figgered away to screw it up.:13:

 

[shredaholic]

Re: Get Your Amp Biased

Quite impressive with the seperate bias pots Shred. Seperate bias pots would allow you bias each power tube individually, therefore allowing you to overcome the difference in a set of tubes, even a "matched" set. Nice.

An amp will sound different at 50% dissapation than it will at 70% dissapation. I use it as a mod technique. Think of it, you could have (2) of the same amps, and biasing them at the 2 numbers above would give you (2) amps that sound a "little different".

No cost.

Yup - another great thing about the adjustable bias for each tube is that you can "un-match" tubes. Up to about 10mA difference should be okay for the tubes, and the more unmatched they become, the less 2nd order harmonics are eliminated, so you can really experiment to see what sounds best.

 

[kmcguitars]

Re: Get Your Amp Biased

That's a trick I need to learn one day.

1st trick you need to learn is how to properly locate and discharge your Filter caps. This is a MUST!! B4 you go poking around in a Amp.

Next you can Google the words Lord Valve Bias He has a excellent tutorial on this subject. Most important while working in a tube amp... THINK B4 You ACT! If your unsure? Take it to a Tech.

 

[SirJackdeFuzz]

Re: Get Your Amp Biased

Great Thread . . .


. . . here's astory you will NOT B ELIEVE !


I have a Blues Jr. (15watter), so i asked my uncle, who is a semi-pro muso since the mid-70's (49 this year) will our local guitar shop be able to re-bias me amp, (slightly hotter) so that i can get that little bit of extra gain whan my pre-amp vol. is max'ed.

(a reasonable question for a semi-pro, right ?)

After aking him, he just lookedat me with a blank face, and asked; "what do you mean bias?

Needles to say i was shocked !!!
What do i say ?
How on earth can i know more about an amps ins-and-outs than a guy thats been playing valve amps (mostly Fenders) since he was 14 ?

After some more "innocent" questions from my side - probably still white as a ghost from the shock - he told me he always just replaced the tube with new ones when ever it needs to be changed !
That goes for pre-amp & power amp tubes !
He tried to tell me something about "back in the day" they used "built-like-a-tank" Phillips tubes, and that they were ten times stronger (inconstruction i assume) than the "pansy" new stuff of today !???

Man, i am confused !!!

But then again, this is the same guy, that tried to tell me that Marshall 4x12 CABINETS are Class A - WTF ?

Is there any Marshall out there that it class A ?

Oh, and my first question goes out to ya 'all too, btw !

Can my lil Blues Jr' be re-biased to run slighty hotter, and thus giving me that extra gain i am looking for !?

OH, and how can i educate mu own uncle on the world of biassing old 70 and new all-tube amps?

Any sites that will explain biassing for old-dawgs !???
(who should know about it even before i was born, and that was '73)


THANX to all !

 

[ratherdashing]

Re: Get Your Amp Biased

My amp's already biased. It spends all day watching Fox News and reading Ann Coulter books.