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RE: LC filters for B+ ...

They certainly behave differently.

Optimum filtering is accomplished by using critical
inductance values along with critically calculated
capacitor values. This type of supply sounds
more musical, and is much more stable, and is
far less injurious to rectifiers when it is choke-input.
That is, when the first item that the rectifier sees is
a choke and not a capacitor.

When the first item that the rectifier sees is a
capacitor, spike generation occurring on the rectifier
output is not properly snubbed, or smoothed, and MAY BE
ENLARGED.

Capacitor input usually sounds dynamic enough, but
not as musical, and certainly not stable, clean, fast,
or solid-sounding. (It's like a fuss-budget whimp on
a mild spastic session)-- well, not quite that bad.
Let's just say, I don't like them.

It is possible to address what is wrong with both of the
above power supplies, although their rather severe musical
shortcomings are very different for each case-- they are
both musically deranged, compared to the best..

Spike reduction at the rectifier output only needs a small,
super-low DCR choke with a high-fidelity bandwidth. THEN,
it can safely be followed by a capacitor, another similar
choke, and another capacitor. This will establish:
(1) good spike suppression, (2) fast, clean transients due
to low-DCR (and inductance) and the associated smaller
capacitor values, which have shorter charge/discharge times--
something essential to musically driving a dynamic speaker.

A dynamic speaker wants current NOW-- not 1/10000th second
too late. If it gets what it wants WHEN it wants it, not later,
then it can be driven far more dynamically on drastically
less power.

The above excellent performing power supply is NOT
capacitor-input, It is a SUB-CRITICAL power supply,
and it is the best thing money can buy.

PSUD2 can easily confirm this if one will look at the decay
lines. If they're jagged, and the peaks & troughs are not all
the same, or the distances between peaks are different, you
have a wrong value in there somewhere.

Hum & Ripple levels, while also important, pale in
comparison to the power supply's decay and recharge plots.
That is what you look at.

It better be smooth all the way, and symmetrical all
the way.

Enter the sub-critical power supply. It solves all of the
problems except one-- it has a slightly higher hum level.
This is addressed when you apply R.F. chokes and small,
high-grade capacitors as local power supplies for your
smaller (or driver) tubes. The higher gain tubes benefit
from additional LOCAL power supply filtering.
KEEP THE DCR VERY LOW.

In short, don't depend on the Main B+ supply to do
everything for you-- it can't and never will.

-Dennis-


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