> Does your intended amplifier use the filament to
> inject the input RF into the tube circuitry, or is
> one side of the filament perhaps tied to the cathode
> pin(s) on the tubes, with suitable bypass
> capacitance in various places?
The former; the tube has a directly heated cathode,
with cathode RF excitation.
> Does your intended design use a set of bifilar-wound
> filament chokes with suitable bypass capacitance on
> the cold end(s)?
Why, yes; it does!
> Does the design of your intended amplifier feed
> input R.F. to the center-tap of a possible filamant
> transformer?
Since there is no filament transformer in this design,
no. The "design" isn't a modification of another,
it's too basic for that, and is essentially new for
this single-unit amp. In fact, as with most of my
projects, I don't even plan on drawing a schematic.
KZ1X design philosophy: If I design and build
something for my own use that is so complicated that I
need a diagram to fix it later, I designed it wrong.
> In the above circumstances there are filament
> transformers with one side of the output tied to
> ground and other circumstances where the filament
> transformer is running with both sides isolated
> from ground and suitably bypassed.
Yes; the latter is a situation similar to the
configuration used with a switching supply to heat the
tube.
There is no planned use of the 5V supply for anything
other than the heater. The 5V switching supply has
only one output, so, no control or bias voltages are
derived from the heater circuitry.
> If you were to substitute the switcher supply as a
> "black box" in place of a filament transformer is or
> are there any considerations relative to the above
> caveats that would cause you concern, (e.g., design
> considerations)?
No.
> One of the criteria my work
> application dealt with when graduating from
> ferroresonant supplies to switcher supplies (other
> than the easily-swallowed cost savings) was the
> effect of a "complex" impedance on the operating
> radio bays, and if the power plants would be
> affected by all the RF. The final score has not been
> tallied yet. The MTBF for the Chinese (Delta)
> switcher supplies versus the MTBF for the older
> ferro's seems to be two orders of magnitude worse,
> and the Flat-Earth Society engineers all say
> "accumulated PLD's," while the D.C. True Believers
> counter with "R.F.hash."
I've heard plenty from those two peanut galleries,
myself, over the last 23 years.
The design center for Delta is right down the street
from where I am typing this note. Shall I stop by and
have a word with them?
> Meanwhile, the Chinese are steadily sending
> replacements for the switcher modules....
Chinese? Eventually they'll get it right. Once that
happens, the old ferroresonant technique will be
relegated to specific applications.
Case in point: The PRC-made 3-500Z bottles used to be
junque; they're now as good as any ever made, and
maybe better. I still don't like them, though.
tnx
Steve KZ1X/4
42.8 year old curmudgeon
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