[Heathkit] How much capacitance

[Carl]

Thats OK when using a Dahl or similar low impedance transformer.

It does not apply to the SB amp line or many others where the transformer is 
designed to self limit the inrush current. In the SB-220 even the filament 
transformer is deliberately designed that way.

In the 220 the step start mod serves to preserve and protect the on-off 
switch. Replacing the PS diodes with 1N5408's is added insurance as SS 
doesnt mean infinite life.

Carl
KM1H



----- Original Message ----- 
From: "Paul Kraemer" <elespe at lisco.com>
To: <heathkit at yahoogroups.com>; <heathkit at mailman.qth.net>; 
<heath at lists.tempe.gov>
Sent: Saturday, August 22, 2009 10:55 PM
Subject: [Heathkit] How much capacitance


> Those following recent discussion on the SB-200 and SB-220 (or any)
> amplifiers and considering replacement of the (6) electrolytic capacitors
> with newer, better, higher capacitance value units might do well to 
> consider
> for a moment the slippery slope down which they may be headed.
> Pick out any book on power supply design and observe what happens to 
> inrush
> line current and diode (same as transformer secondary) current as the
> capacitance value of the filter capacitor is increased by orders of
> magnitude. THEY INCREASE!
> If you are in the design phase of a new product, fine, put in as much
> capacitor as your pocketbook can afford, then pick out the remaining
> components to stand up to the stress.
> 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"
> An argument might be made that Heath would have used larger capacitors if
> they had been readily available 50 years ago. Or, was it a decision which
> involved all the factors in play? Switches, diodes, transformers,
> performance goals, and marketing.
> We seem to have grown to a point in this society which presumes that more 
> is
> better than a lot more is even better still.
> Sometimes more is not better, it is just more.
> 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)
> 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
>
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