On Sat, 21 Feb 2009 22:13:47 -0800, Richard Clark wrote:
On Sat, 21 Feb 2009 19:37:34 -0600, Frnak McKenney
wrote:
--snip--
Google led me to the AAVSO site (www.aavso.org) which led me to the
Yahoo VLF_Group. Aaaaaaaaaaaaaaauuuuuuuggggh! A circuit that can
replace capacitors or inductors? My first reaction is "technology
at a level indistunguisable from black magic".

I don't think I'm in Kansas any more.

Gyrators have been around for a very long time, and can be found in a
billion telephones, one probably within reach of you at the moment.
They use telephones in Kansas don't they, Toto? You can build one
with four components (none of them an inductor) to make an inductor

That's what the man said... I saw the schematics for Gyrators I-III,
and I need to go back and re-read the decriptive text.

more precisely than you could winding one.

That doesn't take much. I've had days recently where I felt like I
could wind a mile of wire around a ferrite rod and _still_ not make
an inductor. grin!

If you truly want to be overwhelmed with the dark arts, try googling
for "magnetic amplifiers." (Art would go ballistic knowing such a
topic was in practice looooong before he left second form.) No tubes,
no transistors, and the orginal "solid state" design. As this may
sound as if it wanders from the subject of RF, add the name Ernst F.
W. Alexanderson to any search.

Noted and filed, but I think I'm beginning to be "overwhelmed by
insurmountable opportunities". grin!

--snip--
( the Mohican antenna circuitry)
Of the five bands (A-E, SW3 positions 5-1), the only one which seems
different is "E", with an additional 130pF cap between the antenna
and the tank circuit.

Is that what you're referring to?

I am merely pointing out the obvious application of a tapped
inductor of the tuned front end serving as impedance match to an
high-Z antenna (the topic of your choice).

Oh. Okay. "Parallel LC (tank) circuit = high impedance. Coil tapped
to match lower impedance". Gotcha. I got lost trying to figure out
your reference to "conventional bands".

... The schematic abounds in examples.

Yup. You don't see many AM/FM radios these days with three tank
circuits per band. grin!

... One
need only substitute values to serve the right frequency band - a
simple exercise in reverse engineering employed since Hertz drew a
spark across a gap at the base of a loop.

Which was, in its own time, pretty close to "magic".

I've been trying to stir some excitement in the one niece and nephew
who are talking of studying engineering next year, but it's tough.
They seem to be so constantly surrounded by wonders that they take
them for granted.

--snip--
... Your learning lesson of maintaining the
chassis ground with the trace is classic too. The discovery of
corrosion brings up the common practice of taking ALL the tubes out
and putting them back in to solve problems.

It's still surprising to me just how often taking something apart
and putting it together again will get it working again. Doesn't
even require mystical passes with my hands (but I occasionally add
them anyway grin!).

... Tightening ALL screws is
another hard learned lesson that bench techs either get or don't get.

Finished with the Mohican this afternoon. I wound up taking out the
eleven machine screws around the IF/audio PC board out (they were
all still tight, FYI). I then ran some fine steel wool around in
the gap and reassembled it; turned out that I had to unbolt the
audio transformer and 1/4" earphone jack to get the lockwashers and
nuts back on four of them. When I finished there was no leftover
hardware, a small miracle in itself.

It still doesn't buzz. (Yayyyyy!)

You probably could have got away with cheaper transistors by also
substituting the bias diodes (56-7s) - but as events bore out, the
transistors were good. If you note the difference between the base
and emitter voltages, there is only about a tenth volt there. If I am
to presume the diode call-out is for an 1N56, it is germanium too.

Oh. A 56-7 is a 1N56? I wasn't sure about substituting them, and
finding any Germanium parts on this side of the Pond is tough.

I was about ready to bypass the entire audio section and wire in a
small LM386-or-similar amplifier in its place. Might still do it
next time.

What is more amazing is this wasn't about the decrepitude of the
electrolytic capacitors which usually suffer with time if they are not
used for a long while.

When I first heard the buzz, my first instinct was to check the
electrolytics. I even tried parallelling the X7 emitter bypass, but
because _that_ time I did it by hooking my jumpers to the component
leads on top of the PC board, the effort had no effect. Ack! Phlbbbbt!
So _close_...

I have to say that those Gyrator circuits are really appealing. I
may throw one togehter just to see what happens. Thanks for
pointing me at them. (Now if someone would just design a "network
component" that replaced _intelligence_ with four components, none
of them involving intelligence... grin!)

Thanks again for your feedback.


Frank
--
Fashion is...a search for a new language to discredit the old,
a way in which each generation can repudiate its immediate
predecessor and distinguish itself from it.
-- Fernand Braudel/Civilization & Capitalism, 15th-18th Century
--
Frank McKenney, McKenney Associates
Richmond, Virginia / (804) 320-4887
Munged E-mail: frank uscore mckenney ayut mined spring dawt cahm (y'all)