[Heathkit] How much capacitance

[Mike McCarty]

Paul Kraemer wrote:

[...]

> If you are working with vintage products with un-obtainium components that 
> you care to prolong the life of you might be well advised to follow the 
> advice of one author "use the minimum capacitance which results in 
> acceptable ripple"

Vintage electrolytic capacitors were generally -20% +80% tolerance,
and one can usually go up to 2x nominal capacitance without running
into problems, on the input cap. After practically anything which would
tend to limit inrush, like a resistor or choke, the sky is the limit.
On the input, however, there is a definite limit to what is advisable.
It is possible to increase the input capacitor if one also adds some
resistance in the rectifier circuitry to limit inrush.

It is also inadvisable to go much higher in WVDC rating. If one uses
a capacitor rated much higer for WVDC, it will unform down to the
actual working voltage, with a corresponding decrease in thickness
of the dielectric film, and consequent increase in capacitance,
possibly leading to the same problem you bring to our attention.
I don't like to go much above WVDC being 2x actual working voltage.

[...]

> To me, the promise of a few more watts resulting from a slightly increased 
> high voltage and possible slightly improved IMD (I'm guessing on that one) 

Capacitors are not sources of power, and increasing total filter
capacitance cannot increase the power capabilities of a power supply.

> just aren't worth the potential damage to other components I can't replace 
> and paying twice as much for filter capacitors as I would need to.
> Just some ramblings for your consideration.
> Paul K0UYA

Well worth the read.

My message may bounce from groups I'm not a member of, and you might
consider forwarding it on to them.

Mike
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