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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:]
> 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)
