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RE: Thanks for the reminder

Posted by Tre' (P) on September 16, 2016 at 18:34:05

In Reply to: Thanks for the reminder posted by 1973shovel on September 14, 2016 at 13:45:31:

"...opinion over the years seems to be that Dynaco's 1.5 H, 200mA C-354 choke is undervalued for that power supply."

The output tubes draw 200ma. so that's a problem.

As for the Henry value, 1.5Hy is better than no inductance. They could have just used a resistor. 1.5Hy is better than that.

When we use a choke as an input choke, to get the full effect of a input choke (each diode, in turn, stays on for it's entire half cycle and therefore the charging current remain low without current spikes) we need to calculate and use at least the critical inductance value.

The definition of critical inductance is the inductance value that will cause the diodes to each, in turn, stay on for the entire half cycle.

That value is calculated by, critical inductance (in Hy) = ((current in amps / voltage) + the DCR of the choke) / 1000

But in a pi filter (CLC, like the Dyna uses) things are different.

"The component value for the inductor can be estimated as an inductance that resonates the smoothing capacitor(s) at or below one tenth of the minimum AC frequency in the power supplied to the filter (100 Hz from a full-wave rectifier in a region where the power supply is 50Hz). Thus if reservoir and smoothing capacitors of 2200 microfarads are used, a suitable minimum value for the inductor would be that which resonates 2200 microfarads (μF) to 10 Hz, i.e. 115 mH. A larger value is preferable provided the inductor can carry the required supply current."

I would think (but I haven't bothered to figure it out) that the 1.5Hy does meet the minimum. More would be better.

Tre'

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• https://en.wikipedia.org/wiki/Capacitor-input_filter   (Open in New Window)

Edits: 09/16/16

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