Mislead on transformer specs ??

[amdx]

I purchased a transformer with the following advertised spec.
"100-Ohm CT to Dual 1.5Meg-Ohm audio Transformer"
I have picture with the data here.
http://i395.photobucket.com/albums/pp37/Qmavam/P1010078.jpg

I need a couple of things cleared up.
First I note two separate 1.5M windings for ZL.
The Zs has a CT. 100 ohm winding.
Does that mean 100 ohms from pin 1 to pin 3 or pin 1 to pin 2?

I suspect the 1.5M actually means 1.5K ohms because I get no where near
the 1.5M ohms I expected. Is that possible?
I'm measuring at 2 khz.

I see the 1.33 x 10^-6 watts ratting, I think that's tiny,
any possibility the 1.5M ohms is correct, I'm just overdriving the
transformer.
I have a nice signwave in and out.

I was hoping to use this for a crystal radio as a high impedance load to
the tank/diode circuit. But I don't think I got what was advertised.
Any advice about how to test this?
Thanks, MikeK

 

[amdx]

I purchased a transformer with the following advertised spec.
"100-Ohm CT to Dual 1.5Meg-Ohm audio Transformer"
I have picture with the data here.
http://i395.photobucket.com/albums/pp37/Qmavam/P1010078.jpg

I need a couple of things cleared up.
First I note two separate 1.5M windings for ZL.
The Zs has a CT. 100 ohm winding.
Does that mean 100 ohms from pin 1 to pin 3 or pin 1 to pin 2?

I suspect the 1.5M actually means 1.5K ohms because I get no where near
the 1.5M ohms I expected. Is that possible?
I'm measuring at 2 khz.

I see the 1.33 x 10^-6 watts ratting, I think that's tiny,
any possibility the 1.5M ohms is correct, I'm just overdriving the
transformer.
I have a nice signwave in and out.

ya, SINEWAVE

 

[amdx]

I purchased a transformer with the following advertised spec.
"100-Ohm CT to Dual 1.5Meg-Ohm audio Transformer"
I have picture with the data here.
http://i395.photobucket.com/albums/pp37/Qmavam/P1010078.jpg

I need a couple of things cleared up.
First I note two separate 1.5M windings for ZL.
The Zs has a CT. 100 ohm winding.
Does that mean 100 ohms from pin 1 to pin 3 or pin 1 to pin 2?

I suspect the 1.5M actually means 1.5K ohms because I get no where near
the 1.5M ohms I expected. Is that possible?
I'm measuring at 2 khz.

I see the 1.33 x 10^-6 watts ratting, I think that's tiny,
any possibility the 1.5M ohms is correct, I'm just overdriving the
transformer.
I have a nice signwave in and out.

I was hoping to use this for a crystal radio as a high impedance load to
the tank/diode circuit. But I don't think I got what was advertised.
Any advice about how to test this?
Thanks, MikeK

Here's a picture of measurements I made. I can't make sense of it.
http://i395.photobucket.com/albums/pp37/Qmavam/TransformerData2.jpg

 

[J. Todd]

I purchased a transformer with the following advertised spec.
"100-Ohm CT to Dual 1.5Meg-Ohm audio Transformer"
I have picture with the data here.
http://i395.photobucket.com/albums/pp37/Qmavam/P1010078.jpg

I need a couple of things cleared up.
First I note two separate 1.5M windings for ZL.
The Zs has a CT. 100 ohm winding.
Does that mean 100 ohms from pin 1 to pin 3 or pin 1 to pin 2?

I suspect the 1.5M actually means 1.5K ohms because I get no where near
the 1.5M ohms I expected. Is that possible?
I'm measuring at 2 khz.

I see the 1.33 x 10^-6 watts ratting, I think that's tiny,
any possibility the 1.5M ohms is correct, I'm just overdriving the
transformer.
I have a nice signwave in and out.

I was hoping to use this for a crystal radio as a high impedance load to
the tank/diode circuit. But I don't think I got what was advertised.
Any advice about how to test this?
Thanks, MikeK

Hi Mike, I think you need to view the _ratio_ of impedances (turns
ratio squared) when matching. The absolute impedances of the windings are
much less important at low power levels.

 

[amdx]

Hi Mike, I think you need to view the _ratio_ of impedances (turns
ratio squared) when matching. The absolute impedances of the windings are
much less important at low power levels.

I'm not sure what I can do with that info.
I bought it as a 1.5 meg ohm to 100 ohm transformer or 122 to 1 turns ratio.
So I'd like to put a 64 ohm set of earbuds on it and see 960,000 ohms.
I don't see how that's going to happen.
MikeK

 

[J. Todd]

I'm not sure what I can do with that info.
I bought it as a 1.5 meg ohm to 100 ohm transformer or 122 to 1 turns ratio.
So I'd like to put a 64 ohm set of earbuds on it and see 960,000 ohms.
I don't see how that's going to happen.
MikeK

So load the sec. with 64 ohms, and measure the pri. impedance.

 

[Baron]

amdx Inscribed thus:

ya, SINEWAVE

That could be the audio phasing transformer for a sideband rig.

 

[amdx]

Yes; 100 ohm 1-3; refer to filament transformer citation standards or
protocol.
It is extremely reasonable that the "M" stands for "thousands".
If you were over-driving the transformer, you would see peak clipping,
and if you monitored input current, you would see exponential-like rise
near the peak.
Best ou could do is drive 50 ohms 1-2 and put secondaries in series for
3K Z.

I measured the DC resistance of the windings, that was enough to convince
me
that I didn't get the transformer that I wanted.or that the company
specified.
Pin 1 to 3 = 75 ohms
Pin 1 to 2 = 37 ohms
Pin 2 to 3 = 37 oihms.
Pin 4 to 5 =130 ohms
Pin 6 to 7= 130 ohms.

Oddities
All measurements at 2 khz, phase shift is near zero
Open circuit, 1 volt into Pin 1 and 3----- I get 1 volt out on Pin 6 and 7.

If I put 1.5 meg ohm between pins 6 and 7, looking into Pins 1 and 3, I see
100 kohms.

100 ohm load Pin 1 to 3---looking into Pin 6 and 7 = 325 ohms
( 0.38 volts ) ( 1 volt )

Then reversed hookup.

325 ohm load on Pin 6 to 7 --Looking into Pin 1 and 3 = 645 ohms.
( 0.75 volts ) ( 1 volt )

I still don't know what this transformer is supposed to transform,
but I do know it is not 1.5 meg ohm to 100 ohm.
Feedback appreciated.
MikeK

 

[Phil Allison]

"amdx"

I measured the DC resistance of the windings, that was enough to convince
me that I didn't get the transformer that I wanted.or that the company
specified.
Pin 1 to 3 = 75 ohms
Pin 1 to 2 = 37 ohms
Pin 2 to 3 = 37 oihms.
Pin 4 to 5 =130 ohms
Pin 6 to 7= 130 ohms.
but I do know it is not 1.5 meg ohm to 100 ohm.
Feedback appreciated.

** The output windings are meant for a 1.5 kohms load.

Some makers in the past use the letter " M " for thousand - derived from
Roman the number system.

A good rule is to multiply the winding resistance by 10 to estimate the
rated load resistance for most audio transformers.


...... Phil

 

[amdx]

How are you measuring impedances?
Describe your method.

I will but you need to pay attention

I copied a circuit that I used years ago to measure transducer impedances.
I built this circuit;
http://i395.photobucket.com/albums/pp37/Qmavam/TheBoardwithnotes.jpg
I connect a signal generator as a signal source so I can vary the frequency
and amplitude.
The circuit puts a current sensing resistor in series with the DUT. (device
under test)
A scope probe is across the current sensing resistor (say 10 ohms). The
scope then displays the voltage across the resistor, with a little math we
know the current through the DUT. (E/R=I)
The second scope probe measures the voltage applied to the DUT.
So now we know voltage and current and a little more math and we know the
impedance.

I have only recently built the board and I had my own questions about it
measuring properly.
So, several times through this transformer measuring, I would get an
impedance, (say 680 ohms) and just as a check I would put a 680 ohm resistor
in as the DUT and verify that the scope had the same amplitudes showing on
the scope as the orignal DUT.
Also the phase can be checked, the phase was always near zero during these
tests.
The board probably isn't real important at 2 khz but at 500 khz or 1 Mhz you
want to tighten
up so parasitics don't interfere.
Here's the schematic of the board, it might help in understanding.
http://i395.photobucket.com/albums/pp37/Qmavam/TheBoardDrawing.jpg
The sense resistor can be changed, I have used 1, 10, 100, 1k, amd 10k ohms
depending on
the impedance I'm measuring. The current sense resistor should be as small
as possible and still develop enough voltage to see o n the scope. I would
be nice to have a signal generator with
a high output amplitude, my HP has about 3 volts max. when loaded 50 ohms,
this works ok.
The voltage is higher or lower depending on the impedance of the DUT.

If I didn't make this understandable, please let me know where I failed and
I will try
to make it clear.
At this point I have requested an RA from the company I ordered the
transformer from.
It is not as advertised and I hope they will change there webpage.
Thanks, MikeK

If the specs on the transformer mean 1500 ohms at pins 4-5 and 6-7, and
you have
1.5k connected to pins 6-7 as in the top example, you should be measuring
about
100 ohms across pins 1-3, not 1.33k. Something's wrong.

I agree "Something's wrong"

 

[Phil Allison]

"Paul Gormless Git."


** What the **** are you posting to ME for ????

I don't usually see Zs and ZL printed on transformers, my
guess is that for the correct operation of the transformer, it wants a
source impedance of 100 ohms, and load impedances of 1.5 megohms on
the two secondaries,

** Absolute BOLLOCKS.

Piss off idiot.

 

[amdx]

This is the same method you posted over on The Radio Board, isn't it?

Yes it is. When I saw the spec's for this transformer and series
connection of 3 megohms,
I thought even with the 1-8khz, + or - 0.2db specification, It might still
work decently for
a crystal radio. It is not to be.

Have you tried the method of measuring the image impedances of a
transformer
that was described there?
Measure the impedance at pins 1-3 with pins 6-7 shorted; call this Zis.
Measure the impedance at pins 1-3 with pins 6-7 (and all others) open;
call this
Zio.

Calculate SQRT(Zis*Zio). This is the image impedance at pins 1-3. This
will be
the impedance to which the transformer will be best matched at pins 1-3.

Do the same thing in the other direction to find the image impedance at
pins 6-7
(measure at 6-7 with 1-3 successively shorted and open).

I have not tried it. Just the DC resistance measurements alone have me
convinced
this is not a 1.5 meg transformer. I just hope to get a return
authorization.
If I get any time, it will be Thursday, I will try it then.
Thanks. MikeK

 

[amdx]

Have you tried the method of measuring the image impedances of a
transformer
that was described there?

Measure the impedance at pins 1-3 with pins 6-7 shorted; call this Zis.

220 ohms

Measure the impedance at pins 1-3 with pins 6-7 (and all others) open;
call this Zio.

108,000 Ohms

Calculate SQRT(Zis*Zio). This is the image impedance at pins 1-3. This
will be
the impedance to which the transformer will be best matched at pins 1-3.

4919 Ohms

Measure the impedance at pins 6-7 with pins 1-3 shorted; call this Zis.

22 ohms


Measure the impedance at pins 6-7 with pins 1-3 open; call this Zio.

105,000 ohms

Calculate SQRT(Zis*Zio). This is the image impedance at pins 6-7. This
will be
the impedance to which the transformer will be best matched at pins 6-7.

1555 ohms

And as a last test, I put 100 ohms on pins 1-3 and the impedance seen at 6-7
is 330 ohms.

None of it makes sense to me.
Anyone see what's going on?
Thanks, Mike

 

[amdx]

The DC resistances you measured, plus the information printed on the xfmr
would
certainly lead one to believe that pins 1-3 are the low impedance side,
and pins
6-7 the high impedance side.

Yet, when you shorted 1-3 and measured 6-7, you got 22 ohms, versus 220
ohms the
other direction. This is very strange.

Can you make measurements at another frequency, say 1 kHz? Can you
determine
the self resonant frequency of the unit at either winding?

These measurements were performed at 2 khz.
Maybe this evening I'll do one more round of measurements.
I'll find resonant frequency.
MikeK

 

[amdx]

The DC resistances you measured, plus the information printed on the xfmr
would
certainly lead one to believe that pins 1-3 are the low impedance side,
and pins
6-7 the high impedance side.

Yet, when you shorted 1-3 and measured 6-7, you got 22 ohms, versus 220
ohms the
other direction. This is very strange.

Can you make measurements at another frequency, say 1 kHz? Can you
determine
the self resonant frequency of the unit at either winding?

.........................................................................................................................
PLEASE note:
I corrected the values above, 22ohm was actually 220 ohms,
and I recalculated SQRT(Zis*Zio). Don't know how I got those wrong.

New set of measurements at 1 khz.

Measure the impedance at pins 1-3 with pins 6-7 shorted; call this Zis.

217 ohms

Measure the impedance at pins 1-3 with pins 6-7 (and all others) open;
call this Zio.

75,000 Ohms ~ 36* phase shift


Calculate SQRT(Zis*Zio). This is the image impedance at pins 1-3. This
will be the impedance to which the transformer will be best matched at pins
1-3.

4034 Ohms

Measure the impedance at pins 6-7 with pins 1-3 shorted; call this Zis.

229 ohms


Measure the impedance at pins 6-7 with pins 1-3 open; call this Zio.

77,000 ohms ~36* phase shift

Calculate SQRT(Zis*Zio). This is the image impedance at pins 6-7. This
will be the impedance to which the transformer will be best matched at pins
6-7.

4119 ohms

SRF 568 khz pin1 to 3
SRF 730 khz pin 6 to 7
What do you make of that?
Thanks, MikeK

 

[amdx]

These latest results suggest that the two windings you measured are almost
in a
1:1 ratio. This is also consistent with another measurement you described
where
you applied 1 volt to a winding and measured 1 volt out at the other
winding.

I don't know how to reconcile these results with the diagram printed on
the
xfmr. It's very strange!!

there could be a lot of capacitance between the windings messing with
your measurements at 2 kHz.

Ground the case.

apply a low z source at a low freq like 60 Hz to the low Z winding.


measure the voltage across the low z winding with a differential
measurement like a meter, or a scope set up with 2 channels to measure
differential.

measure the voltage across the secondary the same way.

compute the turns ratio and z ratio is the sqr root

Mark

Hi Mark,
I had not thought of grounding the shield.
The transformer frequency spec was 1 khz to 8 khz +or-0.2db.
I wish I would have tried this, but I have shipped the transformer
back to the supplier.
Thanks, MikeK