Get Your Amp Biased

[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.

[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.

[Dr.Mavashi]

Re: Get Your Amp Biased

Gear Moron here again, 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.

[J Moose]

Re: Get Your Amp Biased

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

ba-da-bomp!


Sirjack - The Pro & Blues Jr amps have a fixed bias...most EL84 amps do including Vox's.

Anyway, is there anyway to bias an amp at home without taking it to a shop? I've got a multimeter and I've been poking around audio gear all my life so it's not like I'm about to stick a screwdriver across a 60,000pfu cap 'cause I have no idea what I'm doing!

[jerryjg]

Re: Get Your Amp Biased

absolute balderdash! No need to ever rebias. The factory biases the amp for the proprer tube. I have run my amps for 320 years with the factory setings. Just get mil-spec tubes.Forget about biasing.

[shredaholic]

Re: Get Your Amp Biased

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 !???

He's probably right in that respect - tubes made in the heyday of tube manufacture would be far more rugged than those made today, new production right now just can't compete. That's why with most modern production output tubes, you can't have much more than 500v on the screens, and they don't last anywhere near as much as their modern counterparts. A guy called Terry Kilgore over on the Metroamp forum who used to hang around with Eddie Van Halen back in the day said that when a power tube blew, they used to just go to the store, buy one of them and pop it in, no biasing whastsoever.

However, having tubes that are far out of spec with each other would be more of a concern for the OT's lifespan than the lifespan of the output tubes. It could be likely though that decades ago tube tolerances were made to a certain standard in terms of current draw to avoid people needing to rebias - you just buy the same brand of tube and it will have a current draw of within 10mA of your other tubes. If that was the case, that could be why he got away without rebiasing.

[SirJackdeFuzz]

Re: Get Your Amp Biased

. . . i hear what you say !

Thanx "shedaholic" !