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RE: 5R4GY and filter cap values

Posted by Tre' on March 21, 2017 at 09:56:16:
sideliner has this right.
The figure given on the datasheet is not a max or suggested value.
It's a value given the condistion the rectifier tube is under.
That is to say, you can't exceed the peak repeative current rating of the tube.
To know whether or not you are doing that you need to know the voltage, current, value of 1st cap, DCR of all parts, etc.
Then you need to do the math.
The datasheet gives the series resistance per plate (that would be the DCR of the secondary) for the condition under which it states the max uf value.
Again, there is not a "one size fits all" max uf value but there is a "one size fits all" max peak repeative current rating that can not be exceeded without causing damage.
If the DCR of the secondary is higher then you can use larger a cap than the datasheet states. If the DCR is lower then you will have to use smaller cap than the datasheet states.
It's all about the peak repeative current rating of the tube.
BTW a inrush current limiter will solve turn on surge problems but will do nothing to solve the problem of exceeding the peak repeative current rating of the tube.
The peak repeative current is the current that happens every half cycle as the diodes turn on and off.
The larger the 1st cap (and/or the lower the series resistance per plate) the less time each diode will be on, so each diode will have to deliver more current while they are on (to make up for their shorter duty cycle).
Tre'