In article ,
Randy or Sherry Guttery wrote:

Dave Burson wrote:

S-W model R-1822 has a "reactance dimmer" (item 2) with a 6.3 v lamp that
illuminates the band indicators. The bandswitch physically moves the
nameplates over the lamp. The transformer primary appears to be open, and
a
10K resistor across it does provide a little signal to the speaker. C21 &
C14 are listed as 10 mfd, 25 v and 0.1 mfd, 150 v, and both are absent. I
am suspicious that C21 of that value doesn't belong, since the schematic
has
misidentified a C22 elsewhere. Schematic is from Nostalgia Air.
This radio had been severely hacked, but the beautiful cabinet has kept me
picking away at it for a long time.
I've found a little about reactance dimmers but nothing about use in a tube
radio, mostly fluorescent dimmers. I'd really appreciate any explanation
of
the function here and especially thoughts about the caps that parallel the
primary.

What this appears to be is a saturable reactor who's input is the B+
current to the RF/IF stages - which means the less signal strength - the
higher the B+ current - due to AGC bias action.

This is the same idea that "drives" the Philco shadow meter. Low signal
- high current - since the AGC is low - and biases the tube more "on".
Signal strength comes up (as a station is tuned in) AGC goes negative,
turning the RF & IF tubes "down" (less current). As the current through
the primary rises and falls - so does the saturation - effecting the
transformer's coupling.

Now notice the two secondary windings- If the transformer's "coupling"
is working well - the two windings "buck" - the lamp is dim. However -
if the transformer's coupling isn't - the two windings "interaction" is
reduced - and the lamp is brighter.

Oh, the two caps - well the last thing you want is for the AC signal on
the secondary to be "coupled" through to the B+ - so the two caps act as
bypasses to keep the 60 cycle out of the B+.

(shooting from the hip - again - (sigh) - OK guys - what'd I miss?

This circuit is very confusing to me, I don't understand how it is
supposed to work. There seem to be two opposing forces at work in the
saturable transformer. The first is what you point out, that the two
secondary windings are connected so they "buck", so that when the
transformer is saturated by the DC in the primary, the coupling
decreases and the light dims. But at the same time when the transformer
is saturated the inductance also goes down, so even though the two
secondary windings might be not coupled as tightly, their reactance is
also lower which would tend to cause the light to become brighter. If
this is all there is to it the question would be which one of the two
effects is stronger than the other?

But maybe the windings aren't arranged as on an ordinary transformer.
What if we had E-core style laminations with the primary wound on the
center leg and one of the two secondaries wound on each outer leg. The
presence of the center leg would act as a magnetic short and greatly
reduce the coupling between the two secondaries even when the
transformer isn't saturated. When the transformer isn't saturated the
light would be dim because of the high reactance of the two secondaries
in series with the light. When the transformer becomes saturated at low
signal levels the lights would become brighter because of the lowered
reactance of the two secondary halves.

Just another shot from the hip, it would be interesting to know what the
actual disposition of the primary and secondary windings on the the
transformer core is?


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/

John Byrns wrote:


Just another shot from the hip, it would be interesting to know what the
actual disposition of the primary and secondary windings on the the
transformer core is?

Oh good heavens, John, how reckless - shooting from the hip... I'm
proud of you! ;-)

We had a circuit that was similar in a piece of RADAR gear - IIRC the
transformer was pretty standard looking (but then it's been 30+ years).
I think the key here is the the phasing of the two secondaries - with
the core approaching saturation - the mutual coupling would decrease (as
would the inductance itself) and since the phasing is opposed - both
tend to incease the bulb's current...

Am I missing something?
--
randy guttery

A Tender Tale - a page dedicated to those Ships and Crews
so vital to the United States Silent Service:
http://tendertale.com

Morning Glory imdb Flushed Away Film Downloads Thor: Hammer of the Gods dvd download Exorcismus Movie On Line Download Shutter Island Hq download The Kid music download Cyrus film legal Guan yun chang film imdb movie free Red Riding Hood the Red Dirt Rising full dvd movies the Game of Death trailer Suicide Girls Must Die! movie images Watch The King's Speech Full Film Good Quality Arthur film watch full film Unrequited film dvd quality download dvd movie Monsters Watch MacGruber Film In Full download film Next Friday dvdrip watch the whole The Last Airbender film Big Mommas: Like Father, Like Son Hd Download Where Can I Download The Kvinden der dromte om en mand Good Intentions official trailer Boston Girls Movie Theatre Watch Shaolin Full Movie High Quality Perfect Combination Preview Blue Valentine preview Download The Movie The Chaperone Where To Download The Harry Potter and the Deathly Hallows: Part 1 Movie About The Priest download legal divx Let Me In movie Website To Watch Boy Download Superman/Batman: Apocalypse Full Movie Free Never Let Me Go Imdb hd dvd Scream 4 tide Download Red Dirt Rising Full Length Movie

II'm angry, I'll beat!!

This circuit is very confusing to me, I don't understand how it is
supposed to work. There seem to be two opposing forces at work in the
saturable transformer. The first is what you point out, that the two
secondary windings are connected so they "buck", so that when the
transformer is saturated by the DC in the primary, the coupling
decreases and the light dims. But at the same time when the transformer
is saturated the inductance also goes down, so even though the two
secondary windings might be not coupled as tightly, their reactance is
also lower which would tend to cause the light to become brighter. If
this is all there is to it the question would be which one of the two
effects is stronger than the other?

But maybe the windings aren't arranged as on an ordinary transformer.
What if we had E-core style laminations with the primary wound on the
center leg and one of the two secondaries wound on each outer leg. The
presence of the center leg would act as a magnetic short and greatly
reduce the coupling between the two secondaries even when the
transformer isn't saturated. When the transformer isn't saturated the
light would be dim because of the high reactance of the two secondaries
in series with the light. When the transformer becomes saturated at low
signal levels the lights would become brighter because of the lowered
reactance of the two secondary halves.

Just another shot from the hip, it would be interesting to know what the
actual disposition of the primary and secondary windings on the the
transformer core is?


Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/

This may not shed light, since the drawing quality is poor, but there is a
connection detail for the dimmer.

I still don't understand the need for 2 caps of such different values and
voltage ratings.

Dave Burson

Dave Burson wrote:

I still don't understand the need for 2 caps of such different values and
voltage ratings.

Has to do with the caps themselves. The large cap is for the 60 cycles
(actually 50 to 133 cycles); while the smaller cap is for higher
frequencies. I didn't see the power supply schematic - but dimes to
donuts it's full wave- so the ripple frequency is double the AC line
(110 to 120). That's likely to be phase-shifted a bit before reaching
this circuit. The lamp runs on line frequency - and in combination with
the ripple (riding on the B+) it'd be easy to generate some rather
complex waveforms - with some pretty high harmonics. The large cap
"eats" the lower frequncies - however - it's construction limits it's
usefulness at higher frequencies - so there is the smaller one to deal
with those. Look at most any power supply - you'll find smaller value
caps by-passing the main filters.

The voltage is insignificant (within reason). I'm sure the 25V was
overkill (likely the highest voltage across the primary was 10V); but
25V was "common" back then (often found as the output tube cathode
bypass cap). Since a .1 is seldom seen in lower than 150V - that value
was probably stocked on the shelf as well. Even today - most .1 - even
in solid state stuff - are seldom less than 50V. Just a matter of what
was already on hand (big quantities of a common value are cheaper than a
few "special" values even if those special values could be smaller).


best regards...
--
randy guttery

A Tender Tale - a page dedicated to those Ships and Crews
so vital to the United States Silent Service:
http://tendertale.com

"John Byrns" wrote in message
...

Interesting stuff... snipped for brevity.

I'm a neophyte to this circuit, but let me posit a thought.

Perhaps the fact the secondarys being wired in bucking fashion has not as
much to do with the function of the circuit itself as to assist in the
prevention of the AC filament voltage from being introduced into the plate
supply for the 1st. detector and 1st. IF (otherwise it seems to me it would
make a rather effective modulation transformer). Also, it seems to me that
I've seen other radios (if not the specific circuitry therein) that had
tuning lamps that dimmed when tuned on station. I can think of a couple
reasons for this. First and foremost, more light is needed when tuning
across the dial than when on station. Also, this would tend to cause the
dial lamp to last a considerably longer time than normal, since when on
station it would be running at a fraction of it's normal voltage.

On the other hand, when DC saturates the secondary, wouldn't that tend to
make the primary look like a direct short?

Brenda Ann wrote:

Perhaps the fact the secondarys being wired in bucking fashion has not as
much to do with the function of the circuit itself as to assist in the
prevention of the AC filament voltage from being introduced into the plate
supply for the 1st. detector and 1st.

No, the phasing of the two winding to be bucking IS the purpose of the
circuit, and how it works.


IF (otherwise it seems to me it would
make a rather effective modulation transformer).

Still would - that's what those capacitors across the primary are for.


On the other hand, when DC saturates the secondary, wouldn't that tend to
make the primary look like a direct short?

There is no dc in the secondary - only the primary (the primary is to
the right in this circuit). Remember TRANSFORMERS by nature are designed
to operate on AC; DC only "messes them up". In this case - this circuit
is intentionally designed to take advantage of that.

Let's walk through it one more time - but this time secondaries first -
then primary.

First - let's think about the two (secondary) windings as a primary and
secondary - after all - what windings are "called" has to due with their
use, nothing more. If you hooked AC directly to one winding and a bulb
directly to the other - the AC would couple from one winding to the
other and light the bulb (leaving aside current density, etc. for the
moment). If the two windings are 1:1 ratio - 6.3V applied to one would
show up as 6.3V on the other. You could wire the bulb either way (i.e.
"turn it around") and the current would flow through either the same
phase as the primary (ignoring simple inductance) - or 180 degrees "out
of phase". Point being - the two windings are the same - both oriented
on the same core - and form a 1:1 ratio between them. As long as the
core works as a transformer - the voltage couple between them will be
(ignoring losses) 1:1 - the only "variable" would be the phasing - as
determined by how the windings are hooked up.

OK - now lets wire the two windings as shown in the schematic: Both
windings on the same core; both having "equal effect" (1:1). Now when
current (attempts) to pass through one winding - it "couples" to the
other winding - which then generates an equal (but because of phasing)
but opposite voltage - which tends to cancel (buck) the voltage applied
to the first winding. Think of it as two batteries. If two batteries
are wired "nose to nose" with a bulb in series with them - what happens
to the bulb? Nothing. The two voltage "buck" each other - and (provided
the batteries have an equal charge) equilibrium is reached - no current
flows. Same thing with our two windings - WHEN the transformer's
ability to couple is un-imparied.

This "wild card" then - is what makes the circuit useful. This
particular "transformer" is a special kind which unlike the "usual"
transformer (which has modifications to help it "ignore" DC in the
windings) - but rather is designed to indeed easily saturate the core
when (sufficient) DC passes through one of it's windings. As the core of
a transformer approaches saturation - it's ability to couple AC between
the windings starts to fail; to the point that a fully saturated core
couples virtually nothing.

So - in this circuit - when the AGC has the RF / IF stages biased way
down (on station) the B+ current draw is low - which passing through the
primary (or control winding if you prefer) has little effect on the
transformer's ability to couple AC between the other windings - in this
case causing one winding to "buck" the other - and the bulb is dim.
When the AGC falls - biasing up the gain (current) of the RF & IF stages
- the current in the primary (or control) winding increases - pushing
the core towards saturation - and the two windings in series with the
bulb loose their coupling, reducing the induced bucking emf - and the
bulb brightens.

As you noted - when there is significant coupling between the two bulb
windings - that will also couple to the primary (or control) winding.
That's where the two capacitors come into play - they bypass any ripple
impressed on that winding back down to the B+ rail - which of course has
it's own filtering to ground.

best regards...
--
randy guttery

A Tender Tale - a page dedicated to those Ships and Crews
so vital to the United States Silent Service:
http://tendertale.com

Randy or Sherry Guttery wrote:
Brenda Ann wrote:

Perhaps the fact the secondarys being wired in bucking fashion has not
as much to do with the function of the circuit itself as to assist in
the prevention of the AC filament voltage from being introduced into
the plate supply for the 1st. detector and 1st.

No, the phasing of the two winding to be bucking IS the purpose of the
circuit, and how it works.


IF (otherwise it seems to me it would make a rather effective
modulation transformer).

Still would - that's what those capacitors across the primary are for.


On the other hand, when DC saturates the secondary, wouldn't that tend
to make the primary look like a direct short?

There is no dc in the secondary - only the primary (the primary is to
the right in this circuit). Remember TRANSFORMERS by nature are designed
to operate on AC; DC only "messes them up". In this case - this circuit
is intentionally designed to take advantage of that.

Let's walk through it one more time - but this time secondaries first -
then primary.

First - let's think about the two (secondary) windings as a primary and
secondary - after all - what windings are "called" has to due with their
use, nothing more. If you hooked AC directly to one winding and a bulb
directly to the other - the AC would couple from one winding to the
other and light the bulb (leaving aside current density, etc. for the
moment). If the two windings are 1:1 ratio - 6.3V applied to one would
show up as 6.3V on the other. You could wire the bulb either way (i.e.
"turn it around") and the current would flow through either the same
phase as the primary (ignoring simple inductance) - or 180 degrees "out
of phase". Point being - the two windings are the same - both oriented
on the same core - and form a 1:1 ratio between them. As long as the
core works as a transformer - the voltage couple between them will be
(ignoring losses) 1:1 - the only "variable" would be the phasing - as
determined by how the windings are hooked up.

OK - now lets wire the two windings as shown in the schematic: Both
windings on the same core; both having "equal effect" (1:1). Now when
current (attempts) to pass through one winding - it "couples" to the
other winding - which then generates an equal (but because of phasing)
but opposite voltage - which tends to cancel (buck) the voltage applied
to the first winding. Think of it as two batteries. If two batteries
are wired "nose to nose" with a bulb in series with them - what happens
to the bulb? Nothing. The two voltage "buck" each other - and (provided
the batteries have an equal charge) equilibrium is reached - no current
flows. Same thing with our two windings - WHEN the transformer's
ability to couple is un-imparied.

This "wild card" then - is what makes the circuit useful. This
particular "transformer" is a special kind which unlike the "usual"
transformer (which has modifications to help it "ignore" DC in the
windings) - but rather is designed to indeed easily saturate the core
when (sufficient) DC passes through one of it's windings. As the core of
a transformer approaches saturation - it's ability to couple AC between
the windings starts to fail; to the point that a fully saturated core
couples virtually nothing.

So - in this circuit - when the AGC has the RF / IF stages biased way
down (on station) the B+ current draw is low - which passing through the
primary (or control winding if you prefer) has little effect on the
transformer's ability to couple AC between the other windings - in this
case causing one winding to "buck" the other - and the bulb is dim. When
the AGC falls - biasing up the gain (current) of the RF & IF stages -
the current in the primary (or control) winding increases - pushing the
core towards saturation - and the two windings in series with the bulb
loose their coupling, reducing the induced bucking emf - and the bulb
brightens.

As you noted - when there is significant coupling between the two bulb
windings - that will also couple to the primary (or control) winding.
That's where the two capacitors come into play - they bypass any ripple
impressed on that winding back down to the B+ rail - which of course has
it's own filtering to ground.

best regards...
So, what is the design method for a transformer that saturates easily? Ken

Ken wrote:

So, what is the design method for a transformer that saturates easily?

Without getting into a bunch of formulae, etc. (which I'd probably screw
up anyway)... a couple of factors - 1) absolute minimum core to couple
the windings - i.e. magnetically "starved". 2) no gaps in the core - let
the DC current's field circulate well - such that it "interferes" with
the AC field. The core can only hold so much flux - if DC is "pushing"
the field one way -- the AC (when it opposes) is only going to "reduce"
it - not reverse it - (or not fully reverse it) so that the coupling
becomes very inefficient. If you look at most output transformers
designed for single-ended use - they have a gap in the core somewhere.
Obviously - such a gap would not be appropriate for a saturable reactor.

And that sets me pondering again whether the primary "effect" is bucking
or just reactance... Let's say for the moment that bucking is not the
primary mode - and reactance is. Then why the reversed phasing (if
bucking isn't a factor)?

Well - as I just noted - in a true saturable reactor - the DC flux
"overwhelms" the AC flux. Since the AC and DC are additive half the
time - and subtractive half the time - the control isn't going to be
symmetrical. This is overcome in "the real world" by twin reactors -
with the DC "reversed" through one (compared to the other). This way
the "offset" in one reactor is "countered" by the other --- and then
they "switch roles" when the AC reverses polarity. If you look at the
circuit here - (and again - for discussion sake totally ignore bucking)
- the AC is "reversed" all the time at one end - or the other of the
primary -- as the two coils are phase reversed.

Back to saturable reactor theory - when the DC control winding drives
the core into saturation - the reactance in the AC winding drops
dramatically. That being the case with this circuit - then the two
windings would 1) loose coupling so bucking is no longer a factor - and
2) have virtually no reactance in series with the bulb. Then by 1/2 the
AC "reactance winding" reversed - both halves would contribute their
part to the overall source impedance - providing better symmetry.

Now I'm not so sure that pure reactance doesn't play a larger role than
originally thought... That perhaps control is indeed more reactance -
and "bucking" is just a happy "bonus" to the equation...

without taking some measurements (esp. being able to Un-reverse phase
the two windings) - it's hard to guess...

best regards...
--
randy guttery

A Tender Tale - a page dedicated to those Ships and Crews
so vital to the United States Silent Service:
http://tendertale.com