I have an old Jensen-made output transformer from the 1950s (or
perhaps '40s), and because it has unusual wiring, I'm confused about
the connections. (It's the kind that was attached to the basket of a
P12R, P12Q, etc., or maybe to a field-coil speaker; it has 3 1/8"
mounting centers.)

First, the easy part: the transformer has two leads coming out of one
side, and five leads coming out of the other.

Now, the tricky part: the OT has a terminal board on top of it, with
several terminals. The two leads from the one side of the OT are
connected to terminals labeled "Voice Coil" - "1" and "2". Four of the
leads from the other side are connected to terminals labeled
"Impedance" - "500", "1000", "1500", "2000". (There is also label "8",
but it has no terminal, just an empty cutout in the phenolic board.)

Another tricky part: There are two more terminals, labeled "Line" -
"1" and "2". The "Line 1" terminal is connected to the fifth lead from
the one side of the OT. The "Line 2" terminal is connected to a lead
with a quick-release on it; it is now attched to the "500 ohm"
terminal.

Now, the questions:

1) Is this a field-coil transformer?
2) Or is it a single-ended OT?
3) Does anyone have a schematic or instructions?
4) Any other tips you can provide?

One more note: The OT has "ZY2003" stamped on the outside of the
winding wrapper paper.

Thanks for any input you can give me.

--E

Ether wrote:

I have an old Jensen-made output transformer from the 1950s (or
perhaps '40s), and because it has unusual wiring, I'm confused about
the connections. (It's the kind that was attached to the basket of a
P12R, P12Q, etc., or maybe to a field-coil speaker; it has 3 1/8"
mounting centers.)

First, the easy part: the transformer has two leads coming out of one
side, and five leads coming out of the other.

Now, the tricky part: the OT has a terminal board on top of it, with
several terminals. The two leads from the one side of the OT are
connected to terminals labeled "Voice Coil" - "1" and "2". Four of the
leads from the other side are connected to terminals labeled
"Impedance" - "500", "1000", "1500", "2000". (There is also label "8",
but it has no terminal, just an empty cutout in the phenolic board.)

Another tricky part: There are two more terminals, labeled "Line" -
"1" and "2". The "Line 1" terminal is connected to the fifth lead from
the one side of the OT. The "Line 2" terminal is connected to a lead
with a quick-release on it; it is now attched to the "500 ohm"
terminal.

Now, the questions:

1) Is this a field-coil transformer?

No. Field coils are usually excited by a DC supply.

It's use is at the receiving end of a loudspeaker distribution system.
Each of several loudspeakers would have one of these devices.
By using the impedances you have listed on it's input side & driven by
an amplifier whose output includes 70 volt & 140 volt connections it is
possible to service a large area with audio at minimum signal loss.

The various connections make possible a selection of audio power
to be delivered to various locations at different levels as need be.

If you measure the DC resistance from the voice coil leads to the
connections marked 500, Etc you will probably find there to be a
connection. That is because you have an AUTOtransformer, not
a true transformer with separate primary & secondary windings.

The application is public address, not high fidelity.


2) Or is it a single-ended OT?
3) Does anyone have a schematic or instructions?
4) Any other tips you can provide?

One more note: The OT has "ZY2003" stamped on the outside of the
winding wrapper paper.

Thanks for any input you can give me.

--E

On Mon, 17 May 2004 12:41:21 +0000, Ether wrote:
Now, the tricky part: the OT has a terminal board on top of it, with
several terminals. The two leads from the one side of the OT are connected
to terminals labeled "Voice Coil" - "1" and "2". Four of the leads from
the other side are connected to terminals labeled "Impedance" - "500",
"1000", "1500", "2000". (There is also label "8", but it has no terminal,
just an empty cutout in the phenolic board.)

This is a speaker line-matching transformer.

Back the olden days public address amplifiers would
have a 250 ohm output, which would be stepped down to
8 or 16 ohms with transformers mounted on the
speakers, If one had 4 speakers, the line side of
the 4 transformers would each be hooked to 1000 ohms,
thus presenting a 250 ohm load to the amp.


Nowadays they've standardized on 70V or 25V
lines and they mark the primary of the the matching
transformers in watts, ie: if you have a 50 watt
amp, you can hook up, say 5 speakers, each on
the 10 watt taps of the matching transformers.
The reason for the existence of the above arrangement
is twofold, first, electrical codes require special wires
or conduit for wires carrying more than a certain voltage
(usually 25V) in a building. Secondly, electricians
apparently tend to go apoplectic when asked to do
the simple algebra to figure out which impedance
taps to hook the line up to... ;-)

I've seen some very good quality speaker line
matching transformers, but that's unusual, most
of them ain't too great. Given the size I'd guess
it's probably good for 60 Hz to maybe 5 KHz at whatever
wattage it's rated at...on a really old Jensen,
maybe 15 or 25W, which is what the speakers were
usually rated for.

--
Ned Carlson Triode Electronics Chicago,IL USA
www.triodeelectronics.com

I received a very good e-mail response to my question, which I will
share below:

-----------
From: "C.M."

What you have is a line matching transformer, not an output
transformer. It dates to a time before the "70.7 volt line" matching
system came into fashion. (The two systems are equivalent, but the
arithmetic with the "70.7 volt system" is simpler). You select the
impedance you want to present to the line with the jumper, and connect
the line to the two line terminals. This transformer would be nice to
use with a boatanchor shortwave receiver that uses a 500 ohm line
output with no 8 ohm output.

You cannot use this transformer for an output transformer, because the
dc current in the primary will cause core saturation.


Just found your transformer in the 1945 Jensen catalog. It is a
"Model Y" transformer. "Suggested for use with Jensen Models PM12H,
A12PM, B12X, A12, B15X".

So, its intended to handle 12-15 Watts. Other info confirmed as in my
last email.

Price in 1945 was $4.15.

--C.M.

Thanks for the info, Ned.

Given the size I'd guess it's probably good for 60 Hz
to maybe 5 KHz at whatever wattage it's rated at...on
a really old Jensen, maybe 15 or 25W, which is what the
speakers were usually rated for.

Sounds about right. The EIA/Date code on the transformer is 220742; I
assume it was made in 1947.

Oh well--interesting learning experience! Too bad I have no use for
this...

--E

[52telecaster]

[quote=Ether;363771]I have an old Jensen-made output transformer from the 1950s (or
perhaps '40s), and because it has unusual wiring, I'm confused about
the connections. (It's the kind that was attached to the basket of a
P12R, P12Q, etc., or maybe to a field-coil speaker; it has 3 1/8"
mounting centers.)

First, the easy part: the transformer has two leads coming out of one
side, and five leads coming out of the other.

Now, the tricky part: the OT has a terminal board on top of it, with
several terminals. The two leads from the one side of the OT are
connected to terminals labeled "Voice Coil" - "1" and "2". Four of the
leads from the other side are connected to terminals labeled
"Impedance" - "500", "1000", "1500", "2000". (There is also label "8",
but it has no terminal, just an empty cutout in the phenolic board.)

Another tricky part: There are two more terminals, labeled "Line" -
"1" and "2". The "Line 1" terminal is connected to the fifth lead from
the one side of the OT. The "Line 2" terminal is connected to a lead
with a quick-release on it; it is now attched to the "500 ohm"
terminal.

Now, the questions:

1) Is this a field-coil transformer?
2) Or is it a single-ended OT?
3) Does anyone have a schematic or instructions?
4) Any other tips you can provide?

One more note: The OT has "ZY2003" stamped on the outside of the
winding wrapper paper.

Thanks for any input you can give me.

Hi, I know this is an old post, but....I do have this same Jensen transformer new in the box WITH the directions. If you'd like a copy I can send you one.

[52telecaster]

[quote=52telecaster;955319]

Originally Posted by Ether

I have an old Jensen-made output transformer from the 1950s (or
perhaps '40s), and because it has unusual wiring, I'm confused about
the connections. (It's the kind that was attached to the basket of a
P12R, P12Q, etc., or maybe to a field-coil speaker; it has 3 1/8"
mounting centers.)

First, the easy part: the transformer has two leads coming out of one
side, and five leads coming out of the other.

Now, the tricky part: the OT has a terminal board on top of it, with
several terminals. The two leads from the one side of the OT are
connected to terminals labeled "Voice Coil" - "1" and "2". Four of the
leads from the other side are connected to terminals labeled
"Impedance" - "500", "1000", "1500", "2000". (There is also label "8",
but it has no terminal, just an empty cutout in the phenolic board.)

Another tricky part: There are two more terminals, labeled "Line" -
"1" and "2". The "Line 1" terminal is connected to the fifth lead from
the one side of the OT. The "Line 2" terminal is connected to a lead
with a quick-release on it; it is now attched to the "500 ohm"
terminal.

Now, the questions:

1) Is this a field-coil transformer?
2) Or is it a single-ended OT?
3) Does anyone have a schematic or instructions?
4) Any other tips you can provide?

One more note: The OT has "ZY2003" stamped on the outside of the
winding wrapper paper.

Thanks for any input you can give me.

Hi, I know this is an old post, but....I do have this same Jensen transformer new in the box WITH the directions. If you'd like a copy I can send you one.