[Premium-Rx] Racal 17XX speaker

Tue Aug 10 14:28:07 EDT 2010

Greetings!

That front panel speaker is a bit of a paradox.

When I got my first 1772, the speaker in it sounded quite GOOD... it still
does.

On the second and third radios, it sounds like somebody shoved the RCA
pooch head first into the horn!

As has already been mentioned, that tiny speaker is meant as a means of
checking receiver operation locally, not for extended operation... but I've
been keeping an eye open for a very long time now for replacement speakers
that will fit the space and mountings on the panel. So far, no success.

I'm of the opinion that the two bad sounding speakers have warped cones,
and the voice coils are dragging in the magnet gap.

In any case, I'm sort of partial to rack mounted speakers over the operating
position. For the 2 radios set up for diversity I therefore have a rack panel
made up that has two good quality 6" speakers mounted on it. That leaves
nothing to be desired for audio quality.

For the "solo" radio, another rack panel holds an 8" Radio Shack Hi Fi
driver. That's backed up by a plywood enclosure, forming an infinite baffle
speaker. When I made it, I considered adding a reflex port and a tweeter,
but I decided against it; I was tired of sawing and fileing big rack panel
holes!

Comparing it to the audio response of it to the legendary (and overpriced!)
Hallicrafters R-42 Reproducer (an 8" Jensen driver mounted in a steel bass
reflex enclosure) I can't hear much difference.

The RA-1772 is capable of quite good audio reproduction on AM broadcast
signals, especially if the IF filters include the 
8 or 13 KHz. I personally find
the 6 KHz to be a bit narrow.

Distortion seems quite low, at least to my ears.

The response is SO good in fact that it can be a hindrance in applications
that require less response, like SSB; with a good speaker, too much garbage
comes through, even with the IF cranked narrow.

On my fancy "solo" speaker, I found it helpful to 
add a trick from the Hallicrafters
R-42 and R-44 speakers.

I stepped up the audio impedance to 500 ohms, and added the roll-off network
they used; a couple of .5 MFD capacitors (one in 
series and one in parallel with the
500 ohm audio line) , switched in and out of the 
circuit with a DPDT toggle switch
marked COMMUNICATIONS and HIGH FIDELITY. After 
all of this, another 500 / 8 ohm
transformer lowers the impedance again to match the speaker's voice coil.

With this setup, or with any decent receiver top 
speaker, the RA-1772 is an excellent
AM BCB DXing receiver.

Mr. T., W9LBB

At 16:31 09-08-10, Steve Pappin wrote:
>BTW, the manuals can be found here:
>http://www.radiopics.com/Racal/Racal_RA%201772.htm
>
>----- Original Message -----
>From: "Michael O'Beirne" <michaelob666 at ntlworld.com>
>To: "Enrique Fernandez García" <enriqueeeeee2001 at yahoo.es>
>Cc: "PREMIUM-RX" <premium-rx at mailman.qth.net>
>Sent: Monday, August 09, 2010 1:04 PM
>Subject: Re: [Premium-Rx] Racal 17XX speaker
>
>
>
>Dear Enrique
>
>Forget the panel speaker.  The small 2 inch panel speaker is not designed
>for hifi!!!!  It's just there to tell you whether or not there is a signal.
>
>A professional would be listening via nice comfy headphones, and the output
>to his comms system would almost certainly be sourced from the excellent
>quality audio from the 600 ohm line output.
>
>What you need to do is to connect a QUALITY speaker to the 8 ohm output.  I
>use a nice British-made Linn hifi speaker that's physically a lot bigger
>then the panel of the 1772.
>
>A decent station such as BBC Radio 4 LW is not hifi because of the Optimod
>modulation system used ( a sort of compressed AM) but even so the bass
>response of the 1772 via the big speaker reminds me of the lovely old
>"steam" valve radio of my late dad.
>
>Some modern DSP receivers apply far too much bass cut to the audio, even on
>AM.  They are good for "communications" quality SSB and the like but sound
>pretty thin and miserable on a decent AM station.
>
>----- Original Message -----
>From: "Enrique Fernandez García" <enriqueeeeee2001 at yahoo.es>
>To: <premium-rx at mailman.qth.net>
>Sent: Monday, August 09, 2010 5:31 PM
>Subject: [Premium-Rx] Racal 17XX speaker
>
>
>
>I forgot, concerning to the panel mounted speaker, it sounds terrible in my
>1772, I have tried different things such as put some ball papers between the
>cone and the metal with not good results.
>
>Anybody has the same problemm with the speaker? Any solution?
>
>I have already got a Minimus 7 external speaker connected but I do not why I
>like to listen the internal much better.
>
>Regards
>
>
>
>
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