5E3 Build - Intial Test Problem

[boojo35]

I am now tracking what you are saying more clearly and you are definitely spot on as to what caps do in series. People tend to sometimes think that they react like resistors do. You have a great way of dealing with the real high HT circuits in some amps. Good stuff!

[Randall]

Chuck,

I understand how the caps work in series, but could you explain how you come to the 220K values?

[MWJB]

The 220Ks are just an appropriate value to work as balancing resistors to ensure the series caps see an equal proportion of the total B+...a little +/- probably won't hurt. Each cap is bypassed with a resistor.

[Chuck H]

Right. As I mentioned, there IS a formula to figure the ideal resistor values but I don't know it. 220k happens to be a popular default value for this circuit as used by both MFG's and DIY's that also don't bother with the formula. So that's the value I use.

[Bruce / Mission Amps]

Regardless of who made them or how good the "NET" says they are, no two, reasonably priced, electrolytic capacitors are 100% identical.

The basic idea of using the resistors is not really to form a voltage divider but is more to balance, or "swamp" the "capacitive reactance" and leakage of each capacitor.
One will charge faster then the other....
You don't want too low of a total resistance to ground or you will unnecessarily draw current from the B+ rail.
(But a little bit of current draw is actually good for the B+ rail in terms of stability.)
On a 500vdc rail with two 350v E-caps in series with two 220,000 ohm resistors in series, the total load to ground at that point is 440,000 ohms.
500v/4440K = about 1ma, or .001A
That means each resistor is passing 1ma.
On this imaginary 500vdc rail with two 350v capacitors and that divider, each 220K resistor sees 250v@1ma and each resistor uses up about .22 of a watt of energy.
So, to be 100% safe I'd use a pair of 1 watt resistors, but I bet a 1/2 watt resistor would be fine.