Bias filtering

[eeka chu]

I'm putting together a three pin regulated variable bias supply.

Should I get a fitting, hmmm free, result using the 10,000uF per amp rule for capacitance?

Or should I try something higher?

 

[Sch3mat1c]

Er...

*choke*

Just how much current you intending on drawing from this ******* bias supply anyways?!

Oh... per amp... still 5x too much! ;O)

Besides, bias is applied through a grid leak, the other end of which is almost always connected to a low impedance triode. In fact, you can run through the voltage dividers thus represented and find exactly how much ripple actually appears _at the grid_. Then for extra points, determine the CMRR of the PP output stage! (If...that happens to be what you are biasing..)

Tim

 

[eeka chu]

Er...

*choke*

Just how much current you intending on drawing from this ******* bias supply anyways?!

You mean you DON'T weld with your bias supply?!

Oh... per amp... still 5x too much! ;O)

Apparently, if I use tantalum, 125x too much!

Besides, bias is applied through a grid leak, the other end of which is almost always connected to a low impedance triode. In fact, you can run through the voltage dividers thus represented and find exactly how much ripple actually appears _at the grid_.

I think I see what you're saying, but... since the grid can't emit electrons, theoretically anyway..., whilst it's biased negatively it should have a very high resistance between it and the cathode shouldn't it?

"The grid of a tube normally presents a very high impedance load to the driving source when it is biased in the negative region." Aiken of Aiken Amps.

 

[Sch3mat1c]

AC. AC impedance. Backwards, behind the coupling cap, you know...

Otherwise yes, the grid has a high DC impedance - until you overdrive it and it becomes a diode part of the cycle. Hehe..

Tim