02-04-2017, 04:53 AM
(This post was last modified: 02-04-2017, 05:01 AM by Diabolical Artificer.)
Z = out is very roughly your anode resistor, or not so roughly 0.14 - 0.4 x Ra. But strictly speaking Zout is Ra in parallel with the dynamic resistance. Z in is roughly the grid resistor. But this is very approximate because impedance is dependant on frequency, so a gain stage or OPT will have a different Z at 20hz than at 20khz due to valve interelectrode capacitance's and an OPT's inductance. Even then it's hard to find some power valve's capacitance's from the datasheet to base your calculation's on, then there's stray C and shunting C; it can make your head hurt.
The only math's I use in building amp's are ohm's law, f = 1/(6.28xRxC). This can be juggled to find cap and R value's for RC filters and loads of other stuff. About the only other thing I use is multiplying RMS by 1.414 to get peak value or DC once rectified. I manage to wing it without anything else finding it easier to measure stuff once built.
For quick PCB's I use a dremmel to cut out the traces once having drawn the layout on a bit of paper. I use a sharp cutter to cut the traces and drill the holes, then deburr using a round ball bit. Not as neat as etching but quick.
150w OTL amp's! They'll be tricky, what will you use some sort of follower?
Andy.
The only math's I use in building amp's are ohm's law, f = 1/(6.28xRxC). This can be juggled to find cap and R value's for RC filters and loads of other stuff. About the only other thing I use is multiplying RMS by 1.414 to get peak value or DC once rectified. I manage to wing it without anything else finding it easier to measure stuff once built.
For quick PCB's I use a dremmel to cut out the traces once having drawn the layout on a bit of paper. I use a sharp cutter to cut the traces and drill the holes, then deburr using a round ball bit. Not as neat as etching but quick.
150w OTL amp's! They'll be tricky, what will you use some sort of follower?
Andy.
