I wonder if anyone can offer a picture of the variable selectivity
arrangement of
the Eddystone EA12, which I believe was also used by some other
manufacturers?

This was the scheme whereby coupling between the primary and secondary of
IF
transformers was varied nechanically by distancing the two halves of the
transformer
from each other.

I have access to photos showing the operating levers, but what interests me
for
the moment is to have a peek, or peeks, inside the IF cans themselves.

"gareth" wrote in message
...
I wonder if anyone can offer a picture of the variable selectivity
arrangement of
the Eddystone EA12, which I believe was also used by some other
manufacturers?

This was the scheme whereby coupling between the primary and secondary of
IF
transformers was varied nechanically by distancing the two halves of the
transformer
from each other.

I have access to photos showing the operating levers, but what interests
me for
the moment is to have a peek, or peeks, inside the IF cans themselves.




You might find something here.

www.eddystoneusergroup.org.uk

Number 15 "Inductor lore"

J


--
"How we have advanced, thanks to the Machine!" said Vashti.

"The Machine Stops" - 1909

"Mantrid" wrote in message
...
"gareth" wrote in message
...
I wonder if anyone can offer a picture of the variable selectivity
arrangement of
the Eddystone EA12, which I believe was also used by some other
manufacturers?

This was the scheme whereby coupling between the primary and secondary
of IF
transformers was varied nechanically by distancing the two halves of the
transformer
from each other.

I have access to photos showing the operating levers, but what interests
me for
the moment is to have a peek, or peeks, inside the IF cans themselves.




You might find something here.

www.eddystoneusergroup.org.uk

Number 15 "Inductor lore"


I should have said, Restoration Projects, then Number 15

J
--
"How we have advanced, thanks to the Machine!" said Vashti.

"The Machine Stops" - 1909

"Mantrid" wrote in message
...
"Mantrid" wrote in message
...
"gareth" wrote in message
...
I wonder if anyone can offer a picture of the variable selectivity
arrangement of
the Eddystone EA12, which I believe was also used by some other
manufacturers?
This was the scheme whereby coupling between the primary and secondary
of IF
transformers was varied nechanically by distancing the two halves of the
transformer
from each other.
I have access to photos showing the operating levers, but what interests
me for
the moment is to have a peek, or peeks, inside the IF cans themselves.
You might find something here.
www.eddystoneusergroup.org.uk
Number 15 "Inductor lore"
I should have said, Restoration Projects, then Number 15

Well done, that man!

Actually, "No5 Crystal filters and receiver selectivity" has the desired
photo.

Many thanks.

"gareth" wrote in message
...
"Mantrid" wrote in message
...
"Mantrid" wrote in message
...
"gareth" wrote in message
...
I wonder if anyone can offer a picture of the variable selectivity
arrangement of
the Eddystone EA12, which I believe was also used by some other
manufacturers?
This was the scheme whereby coupling between the primary and secondary
of IF
transformers was varied nechanically by distancing the two halves of
the transformer
from each other.
I have access to photos showing the operating levers, but what
interests me for
the moment is to have a peek, or peeks, inside the IF cans themselves.
You might find something here.
www.eddystoneusergroup.org.uk
Number 15 "Inductor lore"
I should have said, Restoration Projects, then Number 15

Well done, that man!

Actually, "No5 Crystal filters and receiver selectivity" has the desired
photo.

Many thanks.

.... AND ... a very good explanation of the Eddystone dial, to boot!

On 05/10/13 17:12, gareth wrote:

... AND ... a very good explanation of the Eddystone dial, to boot!


"To boot" seems quite apt for you, old Bean.

--
;-)
..
73 de Frank Turner-Smith G3VKI - mine's a pint.
..
http://turner-smith.co.uk
..
Ubuntu 12.04
Thunderbirds are go.

"gareth" wrote in message
...
I wonder if anyone can offer a picture of the variable
selectivity arrangement of
the Eddystone EA12, which I believe was also used by some
other manufacturers?

This was the scheme whereby coupling between the primary
and secondary of IF
transformers was varied nechanically by distancing the two
halves of the transformer
from each other.

I have access to photos showing the operating levers, but
what interests me for
the moment is to have a peek, or peeks, inside the IF cans
themselves.


This is the same arrangement used by Hammarlund in the
Super-Pro series. Its been too long since I had a Super-Pro
IF can open to remember exactly how the movable coils were
fastened and guided but the variation was done by a post
coming out the bottom of the can and operated by a cam on a
shaft turned by the front panel "selectivity" knob. Very
simple mechanism. This type of variable selectivity is the
only one with completely symmetrical expansion of the
passband. Those using tapped inductances coupled to the IF
coils, such as used in the SP-600-JX and RCA AR-88, are
nearly as good. Capacitance coupling usually results in
some asymmetry as seen in some Hallicrafters receivers
although the variable pass band in the SX-28 works quite
well.
Later in this thread someone asks about variable
crystal filters. There are essentially two forms: the
original Lamb filter and the later one patented by
Hammarlund in 1938 and first used in the HQ-120-X. The
Hammarlund filter has the advantage that the center
frequency does not vary with the bandwidth adjustment or
when the phasing null is moved around. The Hammarlund
circuit was used in the SP-200, 400 and 600 Super Pro
receivers as well as the HQ series and, in slightly modified
form, by TMC in the GPR-90 and by Collins in the 75A-1,2,3
and 51J series. National and Hallicrafters mostly used the
earlier Lamb circuit. as did Hammarlund in the SP-100
Super-Pro.


--

--
Richard Knoppow
Los Angeles
WB6KBL

WOW!

A very full response, thank-you.


"Richard Knoppow" wrote in message
...

"gareth" wrote in message
...
I wonder if anyone can offer a picture of the variable selectivity
arrangement of
the Eddystone EA12, which I believe was also used by some other
manufacturers?

This was the scheme whereby coupling between the primary and secondary
of IF
transformers was varied nechanically by distancing the two halves of the
transformer
from each other.

I have access to photos showing the operating levers, but what interests
me for
the moment is to have a peek, or peeks, inside the IF cans themselves.


This is the same arrangement used by Hammarlund in the Super-Pro
series. Its been too long since I had a Super-Pro IF can open to remember
exactly how the movable coils were fastened and guided but the variation
was done by a post coming out the bottom of the can and operated by a cam
on a shaft turned by the front panel "selectivity" knob. Very simple
mechanism. This type of variable selectivity is the only one with
completely symmetrical expansion of the passband. Those using tapped
inductances coupled to the IF coils, such as used in the SP-600-JX and RCA
AR-88, are nearly as good. Capacitance coupling usually results in some
asymmetry as seen in some Hallicrafters receivers although the variable
pass band in the SX-28 works quite well.
Later in this thread someone asks about variable crystal filters.
There are essentially two forms: the original Lamb filter and the later
one patented by Hammarlund in 1938 and first used in the HQ-120-X. The
Hammarlund filter has the advantage that the center frequency does not
vary with the bandwidth adjustment or when the phasing null is moved
around. The Hammarlund circuit was used in the SP-200, 400 and 600 Super
Pro receivers as well as the HQ series and, in slightly modified form, by
TMC in the GPR-90 and by Collins in the 75A-1,2,3 and 51J series.
National and Hallicrafters mostly used the earlier Lamb circuit. as did
Hammarlund in the SP-100 Super-Pro.


--

--
Richard Knoppow
Los Angeles
WB6KBL

"gareth" wrote in message
...
WOW!

A very full response, thank-you.


Let's go Beanie, let's go.

"gareth" wrote in message
...
WOW!

A very full response, thank-you.


After I posted this I realized that I forgot a part. In
the Super-Pro there is a phenolic lever between the rotating
cam and the rods from the movable coils. I am not sure why
the rods are not moved directly by the cams. I think
Hammarlund had a patent on the IF variation system but I
don't have the number. The Hammarlund crystal filter is
described in _QST_ Dec 1938, p.33 D.K. Oram "Full Range
Selectivity with the 455 khc Crystal Filter" Oram's patent
is USP 2222043 You can get patents by number from the U.S.
Patent and Trade Mark Office or from Google Patents. The
Google site has the advantage that patents are searchable by
text for _all_ dates and are available in PDF form.
I also have the Lamb patents but it will take some
searching since my file is organized by patent number and
not title. However, they are easily found by doing a Google
search for James Lamb. You will also find his patent for
the famous Lamb Noise Blanker. Lamb had more than one patent
on crystal filters and wrote extensively about them in the
early thirties editions of QST. AFAIK, the first application
of the Lamb filter was in the HRO. The first Hammarlund
filter was in the HQ-120-X and it was later applied to the
Super-Pro. Some Series 100 Super-Pros have crystal filters
as an add-on but these are not the later version. BTW, the
Lamb patent was licensed to James Millen. At the time he was
one of the principles of the National Radio company and is
supposed to have been responsible for the mechanical design
of the HRO.


--

--
Richard Knoppow
Los Angeles
WB6KBL