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

In article ,
Randy or Sherry Guttery wrote:

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...

Is one or the other really necessarily a "bonus", don't they work in
opposite directions assuming the two windings are connected in a
"bucking" configuration? Of course we don't actually know they are
really connected in a "bucking" configuration, we are just speculating
they are because of the way the schematic is drawn.

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

I'm glad you are the one working all this out, I would like to see more
information on the construction of the transformer and the disposition
of the windings before speculating too much. If the transformer is of
open frame construction and is not potted, the OP should be able to
easily determine if an E-core is used and if all the windings are on the
center leg?


Regards,

John Byrns

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

John Byrns wrote:

Is one or the other really necessarily a "bonus", don't they work in
opposite directions assuming the two windings are connected in a
"bucking" configuration?

No - because "bucking" would be dependent on good coupling... Which
happens when the core is NOT saturated - so saturated - not bucking -
bright.

Reactance drops when saturated - so saturated - low reactance - bright.


Of course we don't actually know they are
really connected in a "bucking" configuration, we are just speculating
they are because of the way the schematic is drawn.

I'd be VERY surprised if they are not... 1) why have two windings if
"bucking" (or as I speculated previously -- phase reversal to provide
symmetry) was not needed? 2) why take the extra effort to draw the
schematic that way?

I'm glad you are the one working all this out, I would like to see more
information on the construction of the transformer and the disposition
of the windings before speculating too much. If the transformer is of
open frame construction and is not potted, the OP should be able to
easily determine if an E-core is used and if all the windings are on the
center leg?

Since I don't have "hands on" access - I am left with few options: 1)
guess. 2) offer to see if I can fix the thing. (did I really say that???).

The thing that bothers me about that is if the laminations (assuming
(that dangerous word!) traditional construction) are welded... it might
be extremely tough to get it apart to get at the bobbins... Yes
pictures worth 1K words...

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

In article ,
Randy or Sherry Guttery wrote:

John Byrns wrote:

Is one or the other really necessarily a "bonus", don't they work in
opposite directions assuming the two windings are connected in a
"bucking" configuration?

No - because "bucking" would be dependent on good coupling... Which
happens when the core is NOT saturated - so saturated - not bucking -
bright.

OK, I see we are going in opposite directions on the coupling effect.
If the coupling were perfect when the core is not saturated, then the
light would be as bright as it could get due to the bucking effect of
the two windings. When the transformer becomes saturated decreasing the
coupling, the brightness would have nowhere to go but down due the
residual inductance remaining in the two coils.

So coupling drops when saturated - so saturated - low coupling - dim

This works against the reactance effect you describe below.

Reactance drops when saturated - so saturated - low reactance - bright.

News Flash, I am really liking the theory I advanced a few messages ago
that the "transformer" is not wound like an ordinary transformer, but
instead has one of the secondaries wound on each outside leg of the
E-core.

The reason I am really liking this theory now is that I looked up the
service data for the General Electric E-155 which has the similar
Colorama tuning system, and the "transformer" is constructed exactly as
I speculated in my earlier message. If the S-W "transformer" is built
the same way then it is a whole new ball game.

Of course we don't actually know they are
really connected in a "bucking" configuration, we are just speculating
they are because of the way the schematic is drawn.

I'd be VERY surprised if they are not... 1) why have two windings if
"bucking" (or as I speculated previously -- phase reversal to provide
symmetry) was not needed? 2) why take the extra effort to draw the
schematic that way?

See above.

I'm glad you are the one working all this out, I would like to see more
information on the construction of the transformer and the disposition
of the windings before speculating too much. If the transformer is of
open frame construction and is not potted, the OP should be able to
easily determine if an E-core is used and if all the windings are on the
center leg?

Since I don't have "hands on" access - I am left with few options: 1)
guess. 2) offer to see if I can fix the thing. (did I really say that???).

The thing that bothers me about that is if the laminations (assuming
(that dangerous word!) traditional construction) are welded... it might
be extremely tough to get it apart to get at the bobbins... Yes
pictures worth 1K words...

I have seen several posts in rec.antiques.radio+phono over the years
from people who have rewound the GE "transformers", although I don't
remember who they were from.


Regards,

John Byrns

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

Hi,
John wrote:

I have seen several posts in rec.antiques.radio+phono over the years
from people who have rewound the GE "transformers", although I don't
remember who they were from.

I made some functional equivalents, using modern Arnold tape-wound
cores. Photos, and probably some explanation, were posted on the
Forum at antiqueradios.com, but I can't easily locate them now. It
was several years ago. I still have some of the cores, if I can find
them.

Alan

John Byrns wrote:
In article ,
Randy or Sherry Guttery wrote:

John Byrns wrote:

Is one or the other really necessarily a "bonus", don't they work in
opposite directions assuming the two windings are connected in a
"bucking" configuration?
No - because "bucking" would be dependent on good coupling... Which
happens when the core is NOT saturated - so saturated - not bucking -
bright.

OK, I see we are going in opposite directions on the coupling effect.
If the coupling were perfect when the core is not saturated, then the
light would be as bright as it could get due to the bucking effect of
the two windings. When the transformer becomes saturated decreasing the
coupling, the brightness would have nowhere to go but down due the
residual inductance remaining in the two coils.

So coupling drops when saturated - so saturated - low coupling - dim

This works against the reactance effect you describe below.

Reactance drops when saturated - so saturated - low reactance - bright.

News Flash, I am really liking the theory I advanced a few messages ago
that the "transformer" is not wound like an ordinary transformer, but
instead has one of the secondaries wound on each outside leg of the
E-core.

The reason I am really liking this theory now is that I looked up the
service data for the General Electric E-155 which has the similar
Colorama tuning system, and the "transformer" is constructed exactly as
I speculated in my earlier message. If the S-W "transformer" is built
the same way then it is a whole new ball game.

Of course we don't actually know they are
really connected in a "bucking" configuration, we are just speculating
they are because of the way the schematic is drawn.
I'd be VERY surprised if they are not... 1) why have two windings if
"bucking" (or as I speculated previously -- phase reversal to provide
symmetry) was not needed? 2) why take the extra effort to draw the
schematic that way?

See above.

I'm glad you are the one working all this out, I would like to see more
information on the construction of the transformer and the disposition
of the windings before speculating too much. If the transformer is of
open frame construction and is not potted, the OP should be able to
easily determine if an E-core is used and if all the windings are on the
center leg?
Since I don't have "hands on" access - I am left with few options: 1)
guess. 2) offer to see if I can fix the thing. (did I really say that???).

The thing that bothers me about that is if the laminations (assuming
(that dangerous word!) traditional construction) are welded... it might
be extremely tough to get it apart to get at the bobbins... Yes
pictures worth 1K words...

I have seen several posts in rec.antiques.radio+phono over the years
from people who have rewound the GE "transformers", although I don't
remember who they were from.


Regards,

John Byrns

Byrns wrote: OK, I see we are going in opposite directions on the
coupling effect.
If the coupling were perfect when the core is not saturated, then the
light would be as bright as it could get due to the bucking effect of
the two windings.

NO. If the coupling were perfect, the light would be dim because the two
windings are bucking their max., preventing current flow to the lamp. Ken