[R-390] 500/600 ohm audio to 4/8 ohm speakers

Tue Dec 25 17:34:09 EST 2012

Why fool around with stuff that sort of works, just buy the Hammond 119 
series and be done with it!!  Bernie W8RPW
----- Original Message ----- 
From: "KR4HV" <kr4hv at numail.org>
To: <R-390 at mailman.qth.net>
Sent: Tuesday, December 25, 2012 4:36 PM
Subject: [R-390] 500/600 ohm audio to 4/8 ohm speakers


> First of all, Merry Christmas to all and a Healthy, Happy New Year in
> 2013!!!
>
>
>
> I am posting a chart to help some in using line-to-voice coil transformers
> with military receivers and other audio equipment and  realize this 
> subject
> has  been covered but may be of help to some with a more detailed chart of
> some possibilities (and some that are not)  such as use on the BC-348 
> series
>
> as well as all the Collins  R-xxx derivatives and other receivers. The
> military surplus transformers are getting scarce and can be somewhat
> expensive when found.
>
>
>
> The line-to-voice coil transformers are available in many configurations 
> of
> primary voltage vs. wattage as well as single and multiple secondary
> impedances for speakers.  They are also available with high end frequency
> response specifications for the
>
> purists among us, although, most good PA versions will be completely
> adequate for AM/SSB communications.  They are not do-all, end-all 
> solutions
> but work very well and are cost effective.  Some combinations will even 
> work
> for the very high impedances found on some of the BC series radios.
>
>
>
> I have listed but two of the many manufacturers and models on my 
> spreadsheet
> below.  It's not a rocket science revelation but since I was fiddling 
> around
> and have done the work already it may be of help.
>
> At least one can see right away what may or may not be of help in a
> particular situation.
>
>
>
> I will send a Excel file of the spreadsheet to anyone who wants one and I
> will put it on box.com if I can get logged on today.  Hopefully the copy &
> past version will come through lined up correctly.
>
>
>
> 73,
>
>
>
> Walt
>
> KR4HV
>
>
>
>
>
>
>
>
> PA Speaker Transformer  Watt Taps vs. Equivalent Impedance
>
> KR4HV 12/2012
>
>
>
> (aka Line-to-voice coil transformers)
>
>
>
>
>
>
> These work great for audio matching transformers for military & older 
> radios
> where speaker outputs are
>
>
>
> 500 ohms or 600 ohms.  They can provide better fidelity for SWLing than
> military surplus and are less $ to boot.
>
>
>
> They can be reversed for other audio matching needs. Can provide a good
> input match for external amplifiers
>
>
>
> and even microphones in a pinch (use two back to back) if mounted in a
> shielded case and kept away from power transformers in power supplies.
>
>
>
>
>
> Charts show ratio combinations at a glance.
>
>
>
>
> Some have both 25v & 70.7v primaries and a 4 & 8ohm secondary.
>
>
>
>
> I have included several wattage taps for educational purposes. All taps
> options are not be available & vary per manufacturer/model#.
>
>
>
>
>
> Check Models and pick the one that meets your requirement for primary &
> secondary impedance and power rating.
>
>
>
> They come with various wattage taps and frequency response specs.
>
>
>
> It makes no difference  whether it is 25v or 70.7v if the impedances
> required match the primary & secondary taps.
>
>
>
>
>
>
>
> Example# 1: The Quam TCH70 is rated at 10W & 50 Hz- 20 kHz with 5 
> different
> primary wattage taps & 8ohm secondary.
>
>
>
> Example# 2: The Philmore Brand #MT2570 sold at Fry's  is rated at 10W & 
> has
> both 25v & 70.7v primaries with .625w, 1.25w, 2.5w, 5w & 10w taps  & 8ohm
> secondary.
>
>
>
>
> One should be able to select a transformer with a primary & secondary tap 
> to
> work well with military and some older radios.  There are line-to-voice 
> coil
> transformers with
>
>
> various combinations of primary power & secondary speaker impedance 
> ratings
> as well as frequency response specifications.
>
>
>
>
>
> 25V Line-to-Voice Coil Transformer
>
>
>
>
> Primary taps will be marked C & taps for volts (if dual) and watts
>
>
>
> Primary Effective Impedance
>
> using
>
> Watts Tap
>
> Secondary will be marked C, and taps for 4ohm, 8ohm, etc.
>
>
>
> 1250.00
>
> 0.50
>
>
>
>
> 625.00
>
>
>
>
>
> 1.00
>
> Z=V^2/W - Works Great for 600ohm and also works for 500ohm with small
> voltage gain
>
>
>
> 600
>
>
>
>
>
> 1.04
>
> W=V^2/Zreq.
>
>
>
> 500
>
>
>
>
>
> 1.25
>
> Z=V^2/W - Works Great for 500ohm and also works for 600ohm with minimal 
> loss
>
>
>
> 300
>
> 2.08
>
>
>
>
> 312.50
>
> 2.00
>
>
>
>
> 250
>
> 2.50
>
>
>
>
> 156.25
>
> 4.00
>
>
>
>
> 125.00
>
> 5.00
>
>
>
>
> 104.17
>
> 6.00
>
>
>
>
> 78.13
>
> 8.00
>
>
>
>
> 62.50
>
> 10.00
>
>
>
>
> 31.25
>
> 20.00
>
>
>
>
> 25.00
>
> 25.00
>
>
>
>
> 20.83
>
> 30.00
>
>
>
>
> 12.50
>
> 50.00
>
>
>
>
> 6.25
>
> 100.00
>
>
>
>
>
>
>
>
> 70.7VLine-to-Voice Coil transformer
>
>
>
>
>
>
> Primary Effective Impedance
>
> using
>
> Watts Tap
>
>
>
>
> 9996.98
>
> 0.50
>
>
>
>
> 4998.49
>
> 1.00
>
>
>
>
> 3998.79
>
> 1.25
>
>
>
>
> 2499.25
>
> 2.00
>
>
>
>
> 1999.40
>
> 2.50
>
>
>
>
> 1666.16
>
> 3.00
>
>
>
>
> 1249.62
>
> 4.00
>
>
>
>
> 999.70
>
> 5.00
>
>
>
>
> 833.08
>
> 6.00
>
>
>
>
> 624.81
>
>
>
>
>
> 8.00
>
> Z=V^2/W - Works Great for 600ohm and also works for 500ohm with small
> voltage gain
>
>
>
> 600
>
>
>
>
>
> 8.33
>
> W=V^2/Zreq.
>
>
>
> 499.85
>
>
>
>
>
> 10.00
>
> Z=V^2/W - Works Great for 500ohm and also works for 600ohm with minimal
> loss
>
>
>
> 500
>
>
>
>
>
> 10.00
>
> W=V^2/Zreq.  Works Great for 500ohm and also works for 600ohm with minimal
> loss
>
>
>
> 300
>
> 16.66
>
>
>
>
> 250
>
> 19.99
>
>
>
>
> 249.92
>
> 20.00
>
>
>
>
> 199.94
>
> 25.00
>
>
>
>
> 166.62
>
> 30.00
>
>
>
>
> 99.97
>
> 50.00
>
>
>
>
> 49.98
>
> 100.00
>
>
>
>
>
>
>
>
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