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previous: Dave Stork You shouldn't have to use so much c... -- 11/22/1999 7:04 AM

Re: Bias circuit design?

11/22/1999 3:05 PM
peter	Re: Bias circuit design? Actually it gets a bit messy to calculate because you have the 100k resistor in the charging circuit of the cap, so you don't get the voltage you would expect if you treat it as a straightforward divider. Andrew, something you need to be careful of is that you are charging a 100uF cap through a 100k resistor, so the time constant is 10 seconds-- so if you power the amp up without using the standby, the tubes may get hot before the bias voltage has built up to the right value. That is the advantage of the Marshall circuit with 2 smaller value caps.

11/22/1999 3:05 PM

peter

Re: Bias circuit design?

Actually it gets a bit messy to calculate
because you have the 100k resistor in
the charging circuit of the cap, so
you don't get the voltage you would expect
if you treat it as a straightforward divider.

Andrew, something you need to be careful of
is that you are charging a 100uF cap through
a 100k resistor, so the time constant is
10 seconds-- so if you power the amp
up without using the standby, the tubes
may get hot before the bias voltage has
built up to the right value. That is the
advantage of the Marshall circuit with
2 smaller value caps.

Replies:

Gil Ayan This is How I Do it -- 11/22/1999 4:50 PM
Andrew Re: Bias circuit design? -- 11/22/1999 10:16 PM