Tube Amps / Music Electronics
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|5/3/2006 1:11 PM|
|BK||The Aiken Spreadsheet|
The original one I sent to Scott was old and incomplete. This one as all three common cathode amplifier formuls laid out. Pay close attention to units.
Credit goes to Randall Aiken for posting the formulas on his sie.
Credit goes to me for pain stakingly hand jamming the damn things in. I make no guarantee for their accuracy.
|5/3/2006 1:15 PM|
|BK||The Rk/Ck etc.. Spreadsheet|
I meant Joe not Scott...
|5/3/2006 7:30 PM|
I put together one of my own & had a bunch of questions such as where does he get the 'stray capacitance values he assigned to the calculation for Cin? Perhaps RDH4 page 57. That kind of thing.
Mine works but when compared to Aiken's examples the freq. values have a decimal point & a number of zeros in front of the number that then, oddly enough, seems to match up with his.
It will be nice to compare it to this one & perhaps suss out some of the answers.
|5/3/2006 10:54 PM|
Without looking at any of it, when you have decimal point trouble, it is usually the units you use. When you figure RC time constants, the units are ohms and farads. If you use microfarads, you will be off by 6 decimal places.
|5/4/2006 6:50 AM|
Do you mean the plate-grid and cathode-grid capacitance?
Thats from the datasheet. It varies, depending on whether your tube is shielded or not, but 1.6pF is close enough. A few tenths of a pF is mice nuts. -as I think Wild Bill used to say.
|5/4/2006 9:02 AM|
||Mice Nuts! I agree, however...|
BK & Enzo
Thanks for the info! I know I'm just being anal...
Regarding the 'stray capacitance' I found that Aiken actually added .7pf to Cgp & again to Cgk in doing a calculation of Ci. Found it in Aiken's "Designing for Common-Cathode Triode Amplifiers" in the advanced files at his website.
Although the concept of the existance of stray capacitances was fairly easy to accept I couldn't figure where he got the values. Began looking through RDH4 & found a blurb on pg 51 about stray capacitance & another on pg57. In the latter Smith suggests as much as .6 for hi mu tubes & as much as .13 for low mu tubes. Smith was primarily dealing with pentodes but, from what I read, I could see why Aiken assigned a value for stray capacitance. I just can't figure how he arrived at those particular values.
As to the decimal place issues I converted everything in the Cin, f1, f2, f3 & f4 calc. to microfarads as you deduced. Wouldn't converting to farads introduce even more zeros than I have already.
|5/4/2006 5:07 AM|
Here's a plot of the first circuit.
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