# determining impedance of modulation transformer

Scott Johnson scottjohnson1 at COX.NET
Tue Nov 12 20:49:24 EST 2002

```You may want to use a nominal speech frequency for excitation, such as 400
or 1000 Hz,as the xfmr may not have good response down to 60Hz.

Scott

-----Original Message-----
From: Boat Anchor Owners and Collectors List
[mailto:BOATANCHORS at LISTSERV.TEMPE.GOV]On Behalf Of Ed Lambert" "K1ZOK
Sent: Tuesday, November 12, 2002 10:08 AM
To: BOATANCHORS at LISTSERV.TEMPE.GOV
Subject: Re: determining impedance of modulation transformer

Ah, pretty easy.

The impedance ratio is directly proportional to the square of the turns
ratio.

Take a 120 to 6.3 (or other convenient) filament transformer and feed the
6.3 volt output into the secondary side of the modulation transformer.
Measure the voltage on the primary side.  My assumption is that it will
be greater than the secondary.

This will give you the turns ratio.  Now, square the turns ratio and
multiply that by 6500 and that's the approximate impedance of the
primary.

Ed
K1ZOK

On Tue, 12 Nov 2002 10:29:26 -0600 "john w. king" <jbkking at BELLSOUTH.NET>
writes:
> Have modulation transformer , potted type, and do not know the
> specifications . It was made by Merit Transformer and looks as if it
> came
> out of a piece of Military equipment. The impedance of the secondary
> is
> 6,500 ohms. The impedance of the primary  has been accidentally
> obliterated
>
> The markings are      "PART AM -7195    TEST 10000 V.
>                                       FAMILY 14    GRADE 1    CLASS
> A "
>
> It measures  10 1/2 inches high to top of insulators (all on top)
> The width is 5 3/4 inches and the depth is 6 inches.
>
> It weighs approx 34 pounds.
>
> Does anyone recognize this modulation transformer? I need to know
> the
> impedance of the primary winding. If you recognize the transformer
> or know
> how to measure the primary impedance, PLEASE LET ME KNOW.  I  am
> trying to
> decide if this modulation transformer will work in my Johnson Viking
> Desk
> kilowatt.    Thanks for your assistance. 73,John, K5PGW
>
> -----------------------------------------------------------
> This list is a public service of the City of Tempe, Arizona
> -----------------------------------------------------------
>
> Subscription control -
> http://www.tempe.gov/lists/control.asp?list=BOATANCHORS
> To post - BOATANCHORS at LISTSERV.TEMPE.GOV
> Archives - http://interactive.tempe.gov/archives/BOATANCHORS.html
>
>

-----------------------------------------------------------
This list is a public service of the City of Tempe, Arizona
-----------------------------------------------------------

Subscription control -
http://www.tempe.gov/lists/control.asp?list=BOATANCHORS
To post - BOATANCHORS at LISTSERV.TEMPE.GOV
Archives - http://interactive.tempe.gov/archives/BOATANCHORS.html

-----------------------------------------------------------
This list is a public service of the City of Tempe, Arizona
-----------------------------------------------------------

Subscription control - http://www.tempe.gov/lists/control.asp?list=BOATANCHORS
To post - BOATANCHORS at LISTSERV.TEMPE.GOV
Archives - http://interactive.tempe.gov/archives/BOATANCHORS.html

```