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I don't think I'm the resident expert on biasing, but I'll throw in
my 2 cents. Brian has summarized the issue of biasing quite well -
the setting of a car's idle analogy is a good one. Like any mass-
produced item, power tubes will have slight variances in operating
characteristics from one another. Also, tubes need a brief "burn in"
period so that these characteristics stabilize. Biasing serves to
adjust the amount of current conducted by the tube so that the tube
is operating at it's maximimum potential - and sounds its best.
Without biasing (or with improper biasing), a tube (or tubes) will
just sound plain crappy. It will also shorten tube life and can
cause other components to fail, as Brian mentions. For a good
summary, check out this page from Svetlana:
I guess the good news about biasing in relation to the reverb tank is
that the tank doesn't need to be biased!!! :)
Another good place to buy tubes is Antique Electrical Supply in
Tempe, AZ. Although they primarily cater to the vintage radio crowd,
they also are friendly to musicians. I've never ordered tubes from
them, but have purchased other items - service is fast & friendly.
Check them out at
My favorite "secret" source of tubes is the "hamfest" - a flea market
for the amateur radio crowd. Although tube prices have skyrocketed
in recent years, you can still find some bargains there on NOS stuff.
I've seen some junk radios with pre-amp and power tubes in them that
are worth multiples of the asking price! They have these all over
the country, and are interesting to electronics buffs, if nothing
else. If anyone wants more info, I can look through my "favorites"
to see if I can find the Internet link that will tell you where these
events occur - Summer/Fall is prime time!
For those with good luck/timing, don't forget the garage sale/tag
sale/rummage sale (whatever they're called in your part of the
country if you're in the US). Sometimes there's gold in that old
crap! If you're a scavenger, be on the lookout for old (I mean
early '70's and before) TVs - those had pre-amp tubes and sometimes
power tubes that can be used in guitar amp applications. Of course,
these are becoming more rare these days.
Those aren't the quick & easy ways to get NOS tubes, but they are fun
sometimes (especially if it gets you out of doing yardwork in the
Fall!)
-Dick
--- In SurfGuitar101@y..., "Brian Neal" <bneal@z...> wrote:
> > -----Original Message-----
> > From: Fred Pleasant [mailto:fredpleasant@y...]
> >
> > I've got some questions about this stuff too.. Tubes
> > go for pretty cheap, but what's this about rebiasing?
> > Does that cost a lot of money and what exactly does
> > that do? Also where do you recomend purchasing NOS
> > tubes?
> >
> >
>
> Hi, I am certainly not an expert, perhaps Dick Messick or someone
else can
> chime in here. Rebiasing, as explained to me, is kind of like
setting the
> idle on your car. It is only done on power tubes. I think the goal
is to get
> a set of power tubes to play together nicely. Sometimes you see
tubes sold
> as a set and if you install them together no rebiasing is needed
(because
> the manufacturer feels these tubes have "close enough"
characteristics). To
> confuse you worse, some tubes don't need rebiasing. If the tubes
aren't
> adjusted right to work as a set, they can draw too much current and
burn
> out, or even take out your transformer too.
>
> Check this page out. You can buy NOS tubes from them, plus they
have lots of
> FAQs and links to other tube sites. I've seen these guys
recommended on the
> Fender Forum. If you poke around on here long enough you may find
some
> answers.
>
>
>
> BN
