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Great links, Roland! That first one is particularly good for the
safety section - like Brian said, tube circuits have *lethal*
currents - you can't be too careful! If you're not sure, have a pro
do it until you gain enough knowledge to work on the amp safely.
I learned about how dangerous capacitors can be "the hard way"
several years ago . . . and it wasn't even in a tube circuit! I
built a homemade Van de Graaf generator (you know, one of those
things that makes your hair stand on end if you grab the top
terminal) and charged up a homemade Leyden jar type cap. This cap
was built from a small prescription medicine bottle with aluminum
tape on the outside - it was stuffed with steel wool and had a copper
wire going through the lid as the other terminal. I would charge
that little thing with the Van de Graaf generator . . . once, I
*thought* it was discharged - but it wasn't. I grabbed the cap with
both hands and could feel the shock travel across my chest - very bad
situation! The shock actually made my chest muscles involuntarily
contract so that my hands smacked together - picture a non-body
builder doing the "crab" pose! Not a comfortable feeling!
Since then, I've tried to be super careful with *any* project
involving electricity. Sorry about the long story, but it just goes
to show that it doesn't take much to fry yourself! Whatever you do,
be careful!
-Dick (with 8 lives left)
--- In , "roland.bettenville@p..."
<roland.bettenville@p...> wrote:
> For those who want to know more about tube amps and biasing, a good
place to start is the tube amp faq
>
> More technical and with more math but very interresting is the tech
info at
>
> ------------------------
> wrote:
> ------------------------
>
> >Its my understanding there are two ways to bias an amp. The old
school
> >multimeter approach, and the oscilliscope approach. I've heard
some pretty
> >knowledgable people on the Fender Forum denounce the oscilliscope
method.
> >With the multimeter approach you simply measure the current at
some point in
> >the circuit, while tweaking a variable resistor until you get it
into the
> >right range. The exact point to measure the current and the magic
resistor
> >to tweak will all vary according to your amp circuit.
> >
> >This web page shows you how to do it for the Hot Rod
DeVille/Deluxe family
> >amps:
> >
> >Its bound to be different for a Bassman.
> >
> >My advice would be to get a tech to do it for you. The power
supply filter
> >capacitors can store *lethal* voltages for days, so its best to
know what
> >you are doing for your sake and the equipment's. Don't get me
wrong, you can
> >hang out on the Fender Forum and/or find web sites that tell you
how to do
> >it. Its not rocket science. You do have to know what you are doing
though.
> >
> >You can also buy these "bias meters" that plug right into your
tube sockets.
> >These may be handy if the resistor to tweak is already accessible
without
> >taking the amp out of the chassis. However, these are expensive,
and if you
> >have a multimeter already you are probably wasting your money.
> >
> >Good luck,
> >BN
> >
> >> -----Original Message-----
> >> From: D. P. [mailto:noetical1@y...]
> >> Sent: Wednesday, March 12, 2003 3:59 PM
> >> To:
> >> Subject: [SurfGuitar101] setting tube bias
> >>
> >>
> >> Hi group:
> >>
> >> Many of you all seem to be quite knowledgeable about amp mods and
> >> fixes. My question seems simple: I need to learn how to adjust
and
> >> set the tube bias for my 1963 Bassman 50...I have NOS GE 6L6's
that
> >> need to be installed...
> >>
> >> will I need an oscilloscope or any other specialized tools?
> >>
> >> does anyone know a cool link that describes the bias process?
> >>
> >> should I just forget about the DIY and seek the assistance my
> >> friendly amp tech?
> >>
> >> as always, any wisdom shared would be appreciated,
> >>
> >> dp
> >>
> >> (ps: the Bassman 50 through 4X12" Celestion/Utah cab with
outboard
> >> Fender Reverb sounds awesome...sort of like Brian Setzer but
> >> surfidelic)
> >
> >
> >
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> >
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> >
> >
> >
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> >
