> the tube is drawing 7ma no matter what
Well, probably it is acting like a 285V/7mA= 40K resistor. Not exactly, but near enough for government work. If you short the 15K resistor to give a B+ of 390V, it might then draw 10mA (and be at some risk of overheating); if you raised the 15K to 40K I'd expect maybe 190V and 5mA (and low overload level).
That part is fine.
> with 15k and 22u, the other time with 4.7k and 22u. I used the equation 1/(2pi*CR). The answers were realllly tiny. Like 1.5x10^-6 and 4.8*10^-7.
You have decimal places spilled all over the floor. {EDIT... Stamler beat me....}
6.28 * 15,000 * 0.000,022 = 2.07
1/2.07= 0.48Hz.
We have 120Hz ripple. We want to filter it. All we have is a low-slope filter similar to a treble control.
If a treble control has a 1KHz corner, and we play a pure flute tone at 1KHz, will the treble control reduce it? Hardly at all. The treble control does have effect on cymbals at 5KHz-15KHz. The effect on stuff 10 times the corner frequency is musically significant, but will not make cymbals vanish.
We want the buzz to VANISH. So we invent a treble-cut filter that starts much-much lower than 120Hz. 0.5Hz is much-much lower than 120Hz. About 250 times lower. And as a rough approximation, it makes the buzz 250 times smaller.
> the power tx is center tapped
265VCT is also called 132-0-132. You can ground the center-tap and use two diodes to get 132VAC*1.414= 187VDC. That's great if diodes are costly (they used to be) and you only need 180VDC. But diodes are cheap and you want more voltage. So you "misuse" the transformer, or use it in a way it was not designed. Use the whole 265V winding into a 4-diode bridge, and tape-off the CT wire. Don't connect it to anything or there will be trouble!
(Actually, if you needed both some ~300V and a lot of ~150V, you could use the CT wire; but you don't.)
I said "misuse". The CT tap might have less insulation than the outside ends. If you fool with 2,000VCT transformers, you need to ask the maker (ha!) if the CT needs to be held to a low voltage. But on a little 265V winding, not an issue.
:green:
