[MRCA] Radio Shack Mini Amp/Spkr

[Tim]

Hi Breck - I agree!  Very handy little amp/speaker.  I routinely use one
while demonstrating Fox Hole, crystal or Canteen radios for a group so
everyone can listen in.  I also use mine with the GRC-109 or RS-6 sets for
the same reason but also to better distribute the receiver system gain.
Basically  adjust the RF/IF gain controls for best reception and Signal/BFO
interaction, then adjust the amplified speaker gain for a comfortable
listening volume.  Makes a big difference when you need to actually use
these sets for comms (versus "mil-spec demo's")  They are just an LM-486
400 mw amplifier IC but everything else needed is there.  Easy on 9V
batteries, very handy.

I also need to modify the bandpass design of one of mine to peak the gain
around 700-900 cps for CW operation to improve audio SNR while operating CW
with these broad receivers.  And Roger on the blocking cap addition.
Get Some!
Tim
N6CC

On Sun, Mar 29, 2015 at 11:54 AM, B. Smith <smithab11 at comcast.net> wrote:

>       As I am sure everyone is aware Radio Shack is undergoing some
> reorganizing while they are in bankruptcy. Before major changes take place
> I would recommend that members consider purchasing one of their Mini
> Amplifier/Speaker units.  Stock number 277-1008. These small speaker
> amplifiers  are self contained and run off of an internal 9 volt battery.
> They make excellent "field speakers" and are really handy on the work bench
> for trouble shooting.  An excellent addition to an emergency "GO" kit.
>
>        Over the years that I have utilized these mini amp/speakers, the
> overseas manufacturers  have improved the audio response and gain of the
> circuit and changes have been reflected in the latest model "C".  The unit
> makes and excellent microphone preamp etc and is perfect for boosting the
> handset audio of the military sets.  I often paint the ribbed enclosure  OD
> or black to match the equipment in use. On the early models  the schematic
> was pasted inside the rear cover military style but they no longer do this
> and the schematic is not included in with the latest model. But  -    -
> -    I have the schematics for the latest "C" model.      :-)
>        My only criticism of the unit is that it does not have a DC
> "blocking" capacitor for use on vacuum tube equipment trouble shooting but
> this is easily  done by adding a 10uF cap  in the input lead when necessary.
>
> Photos and especially the posted video clips show the amp/speaker in
> action during the anniversary Moose and Squirrel net last November.
> http://k4che.com/MSnetnov14/MSNov14.htm
>
> Z
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