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

Tue Dec 25 18:20:16 EST 2012

Several reasons why we "fool around" with PA line xfmrs:
o enjoyment -- It's fun experimenting with new circuits,reusing old parts, and more.  It's why some of us are stillin the shack soldering away messing around with vacuumtube circuits.  It's fun ... to some of us.
o cost -- a PA line xfmr, especially one from RS, costs a lot less expensive than a Hammond xfmr.
o junk box tradition -- most of us older hams have many ofthe PA line xfmrs in our junk boxes in the shack, just waitingto be put back in service again.  
o satisfaction -- there is something very satisfying, about figuring out a way to repurpose an electronic component.Lots of articles in QST, CQ, and 73, among other magazines, inthe 1940's, 50's, 60's, 70's and 80's gave us ideas about utilizing components in ways they weren't originally intended.Remember the Hinks and Kinks column in QST?!  Usinga PA line xfmr the way suggested by the poster works.  I'vedone it on my R-390A's many times.
The above are just a few of the reasons we fool around withreinventing ways to use electronic components and otherthings around the shack and shop.  Other folks on the listprobably have additional thoughts.73's,-Tom KE4RHH

> From: qedconsultants at embarqmail.com
> To: kr4hv at numail.org
> Date: Tue, 25 Dec 2012 17:34:09 -0500
> CC: r-390 at mailman.qth.net
> Subject: Re: [R-390] 500/600 ohm audio to 4/8 ohm speakers
> 
> 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
> >
> >
> >
> >
> >
> >
> >
> >
> > ______________________________________________________________
> > R-390 mailing list
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> > Help: http://mailman.qth.net/mmfaq.htm
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> >
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> > Please help support this email list: http://www.qsl.net/donate.html 
> 
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