[AMRadio] Ranger Audio... the numbers

Mike Dorworth, K4XM k4xm at arczip.com
Sat Nov 18 15:12:48 EST 2006

Audio transformers are rated for impedance step up or down. It is ,of
course, the square of the turns ratio. A simple check is a known voltage at
1 khz, say 1 volt, and read the voltages of the windings. The z can be
determined by applying a ac voltage at a frequency of interest and placing a
resistor in series with the winding and adjusting the resistance until the
same voltage is on both. The resistive value is equal to the z of the
winding. The peak voltage, RMS times 1.414 must equal the B plus, in this
case 550 volts or so in order to modulate 100 percent. Also, even thougth a
1614 is a healthy 6l6 a 6l6 is not a 1614. One (the 6L6) is rated by any
manufacturer at 360 volts MAX and the 1614 is 550 volts, hey, the same as
the Ranger Power supply, Imagine that! Also lest we forget the modulating
load is the B plus divided by the current. The RF tube load impedance is the
Voltage divided by TWICE the current. The tank values and operating Q
depends on operating at the designed value. Ditto the load the modulator
On z's of windings the transformer need not operate at the stated z, as long
as the ratios are correct. Too low of frequencies would not have enough iron
and too high would make it jump through the capacity instead of the iron.
But a 2 to 1 at say 6000 to 3000 ohms would work fine a 12000 and 6000
ohms..or 3000 to 1500 ohms. Transformers for light commercial service and
amateur service are rated for a certain amount of DC in the windings, these
can not be exceeded or the thing will become a magnet and not work.
Saturation, I think they call it!

Hope this hepls a little. 73 Mike

----- Original Message ----- 
From: "Jack Schmidling" <jack at schmidling.com>
To: "Mike Dorworth, K4XM" <k4xm at arczip.com>; "Discussion of AM Radio in the
Amateur Service" <amradio at mailman.qth.net>
Sent: Saturday, November 18, 2006 10:14 AM
Subject: Re: [AMRadio] Ranger Audio... the numbers

> Mike Dorworth, K4XM wrote:
> > Ranger modulation Transformer
> >
> > 33 watts voice
> >
> > Primary 7083.8 ohms plate to plate. Red is ct.
> > Secondary 3571 ohms. Black is ct. 892 ohms each side to tridode grids.
> You lost me here.  The manual says 100 ohms and 28 ohms respectively
> > 1.9837 Z stepdown ( nominal 2:1)
> >
> > 1.4085 step down turns ratio..
> I guess we are talking z vs resistance.
> So, how does one measure the Z of a transformer?
> If I put a 1khz sig in one end should the amplitude drop by the z
> stepdown ratio?
> js

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