On Fri, 19 Sep 2008 06:45:30 +0300, "Joe"
wrote:


"Jeff Liebermann" wrote in message
.. .
On Thu, 18 Sep 2008 22:15:27 +0300, "Joe"
wrote:

To clarify the circuit, the postive side of the speaker receives 17 volts
thru one diode and a resistor and the negative side is connected via
transistor to ground and the transistor is driven by 4001 IC.

What value resitor?
What's the part number on the speaker?

I just happen to have the manual for a similar Heathkit GC-1005
"Electronic Clock" handy. No specs on the speaker (401-163). The
circuit is similar in that the speaker has one lead going to the
collector of an MPS-A20 and the other to 18.5VAC (not DC) through a
diode and 1200 uf to ground for a DC voltage of 25.7VDC. No resistor
in series.

So, let's do the math. My guess(tm) is that 1 watt will be
sufficiently loud to wake the dead. Yours has about a 15VDC swing.
Assuming a 50% duty cycle and a pure sine wave (yeah sure):
Power = E^2 / R
1 watt = 15^2 / R
R = 225 ohms.
So, it's probably a high impedance speaker of some sorts. I have the
digital clock and an LRC meter and could probably measure the
impedance. If you can't get the info any other way, bug me and I'll
rip it apart.

Speaker is a 401-163
Resistor is 150 ohm
-Jan

Ok the speakers are the same. 225 - 150 = 75 ohms which would be my
guess for the proper speaker impedance. I don't know what value to
suggest based on these calcs. I guess I have to meaure it. That's
going to be rough because the speaker is UNDER the PCB. Give me an
hour or so.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558