[R-390] R-390 Non-A...have a question

[KR4HV]

John & Roger, here is a link to my file on Box.com that may help someone. It
is a chart that details some parameters of common public address line to
voice coil transformers.  They will work well in this application. If you
are an audio purist you can even buy very high quality Hi-Fi ones for high
$$ vs the $4-10 ones I use.  Hi! Hi!

Copy and paste in browser(a .pdf file)
https://app.box.com/files/0/f/554495476/1/f_5314152110

Both this PDF and an Excel file are on box and open to all to download if
you like.

Enjoy your R390A!


Regards,

Walt
KR4HV
kr4hv at numail.org

"There is no excuse for doing a job poorly.  Just do it right.  If you don't
know how, engage someone that does"  WM

"It is now more difficult to obtain a driver's license in most states than
to obtain an Amateur Radio license. Citizen’s Band déjà vu."WM

"Why would one celebrate an eight year old obtaining an Amateur Extra Class
license? Isn’t it very demeaning to that license class, the examination, the
entire licensing process and Amateur Radio? Think about it."WM



-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net]
On Behalf Of Roger Ruszkowski
Sent: Sunday, March 16, 2014 2:58 PM
To: r-390 at mailman.qth.net
Subject: Re: [R-390] R-390 Non-A...have a question


John,

You have to remember the Audio out is 600 ohms and only a 1/2 watt at best.

There is no indication in your post that you have used a 600 ohm speaker or
that you are running a transformer (70 volt  speaker transformer) between
the output and your speaker.

How much power out are you getting.

Your AC volt meter may have a DB scale on it or you can read AC volts and
convert  the value to watts. you are looking for about 15 to 17 volts AC
across a 600 ohm resistor ( two each 1200 ohm in parallel makes a nice 1/2
or 1 watt load resistor).

You may have poor audio output. But you only get a 1/2 watt and if you are
not matching the 600 ohm output to the speakers the level will be very low.

Radio shack use to have matching transformers mostly used for taping several
speakers in an area to a single PA amplifier. they come under several names
and in different power ratings. As you only have a 1/2 watt to work with any
4 or 5 watt size will work. Some pair of taps on the primary and some pair
of taps on the secondary will match the 600 ohms to a 4 or 8 ohm speaker or
set of head phones and provide good listening level audio. If you need more
than the 1/2 watt then use the line out audio into a PA amplifier and
speakers.

Roger AI4NI
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