[Elecraft] Replacement amp for my Motorola Amplified Spkr

[Tom Hammond]

Good evening...

First of all, THANKS so much to the many folks who took the time to respond 
to my plea for information about AF amplifier ICs which might be suitable 
for a replacement amplifier in a Motorola Amplified Speaker which had been 
cross-connected to 12VDC and rendered unconscious.

A number of various schemes and amplifier ICs were suggested, but I finally 
went with the TDA2003 10W automobile radio AF amp IC. This IC will put out 
10 watts when powered by 24VDC, but it'll still put out 5W-12W when powered 
by 12VDC and driving a 4-Ohm speaker. It plays nicely with a single-ended 
12VDC (actually more like 14.2VDC) supply, and my K2 drives the snot out of 
it, if I ask it to do so, which is NOT necessary to fill the room... even a 
noisy room.

My design offers a couple things the original Motorola circuit didn't:

   1) Jack for an external speaker, and
   2) An INPUT volume control

The TDA2003 draws only 36mA of current in its quiescent state and the 
TO-220 IC only gets a bit warm under normal operating conditions, so only a 
modest heatsink is required. The one I'm presently using is probably 
overkill... and it's less than 2" square..

I have placed on my web site at:

    http://www.qsl.net/n0ss

a 190kB PDF which gives some details of the project... schematic, and PC 
board layout. There are also a few pictures of the completed project on the 
web page as well.

Several folks wrote to me, asking to be notified when I found a workable 
solution to my problem. I think this is it. If you have a dead Motorola 
amplified speaker, this might be your salvation too.

I will make a few PC boards (specific to THIS amplified speaker) available 
for those who need them. I have not yet arrived at a price, but I think it 
will be reasonable. If you want to make your own PC board, I'll be happy to 
provide you with as much assistance as I can muster.

If there's enough interest, I may also draw up a much more compact PC board 
for the amplifier alone. But that's a little bit off and it will depend 
upon demand for the PC board.

Enjoy.

73,

Tom Hammond    N0SS