[Boatanchors] 70v line transformer question

[Al Parker]

Hi Greg,
    Yes.  Here's the info I've saved.  I try to incl. the source, didn't
get it on the last one.
73,
Al, W8UT
New Bern, NC
BoatAnchors appreciated here
http://www.boatanchors.org
http://www.hammarlund.info
===========================
10/19/00
Don -
Speaker matching transformers are marked with the power delivered to the
indicated impedance speaker when the distribution line is at 70.7 volts -
corresponding to maximum power output from the audio amplifier driving the
line. This makes it possible to lay out a sound system without any
algebra....just make sure the sum all the individual speaker transformer
power selections matches the amplifier rating..

To find the the impedance, looking into the primary of a transformer:
divide the (rated primary voltage squared) by the rated power delivered to
the speaker (the marking on the secondary tap).

So:  (70.7v) squared / 10 watts  yields 500 ohms impedance  looking into
the primary....just what you want to match a typical boatanchor to a
speaker.

Chuck  N7RHU
=================
10/19/00
Permit me a formula or two.  Power = Voltage squared /
Resistance.

So, Resistance = Voltage squared / Power.

Voltage squared = 70.7 x 70.7 = about 5000.

The 10 watt tap will then correspond to an impedance of
5000/10 = 500 ohms.  The 5 watt tap would correspond to an
impedance of 5000/5 = 1000 ohms.  Your best bet to match 600
ohms is to use the 10 watt tap.  As I recall, I've got one
or two transformers like yours, and the 10 watt tap does a
good job for me.

Jim, W8KGI
===================
More on using 70 volt transformers to match impedances. Here is a list of
watts taps verses impedance;

.31watts 14000 ohms
.625w 7000  ohms
1.25 watts 4000  ohms
2.5 w 2000  ohms
5 watts 1000  ohms
10  w 500   ohms
12 watts 360   ohms
24 watts 180   ohms
40 watts 110   ohms

Here is the chart for 25 volt speaker transformers:
.31 watts 1680  ohms
.625 watts 840   ohms
1.25 watts 440   ohms
2.5  watts 220   ohms
5    watts 120   ohms
----- Original Message ----- 
From: "Greg Mijal" <bluebirdtele at earthlink.net>
To: <boatanchors at mailman.qth.net>
Cc: <glowbugs at piobaire.mines.uidaho.edu>
Sent: Friday, November 24, 2006 3:19 PM
Subject: [Boatanchors] 70v line transformer question


Hi:
Can a  tapped 70v audio line transformer be used to transform a 500 ohm
reciever audio output to a voice coil of 4 - 8 ohms?
I tried it here and didn't work.  Someone told me to try this and I wonder
what jumpers need to go in to make it work.
Thanks
Greg
WA7LYO
in sunny Feenix