[Frequency Division]

How can i reduce a 4mhz frequency to a 10hz freq?

You can also use a multi stage Ripple counter;  every stage will divide the input frequency by 2 and so a 16 stage counter will output a frequency of 61.03515

Some extra logic will be necessary to correct the output and to further divide to 10 Hz.

CMOS Ripple counter datasheets:

CD4020BC.pdf

[Help! I have a Really Weird Part]

It can be a shockley, but its behavior when voltage drops to +10 V is a bit weird;

[Clocks - Integrated?]

A 4060 is even better than the 4020 because you can use its internal ports to create the 32768 kHz, as in the circuit and datasheet below:

CD4020BC.pdf

[Clocks - Integrated?]

I know I could build a 60hrz counter useing some 555 timers (yeah me and thoes 555s...) but i'd like something much more accurate.

Do you know of a good way to do this? Maybe an integrated curcuit of some sort?

A very simple and accurate way is through a 32768 kHz crystal oscillator followed by a clock divider.

dt26_dt38.pdf

[Whats a switching diode?]

Switching diodes are fast diodes that show low losses when used at medium/high frequencies.

[Not working link!]

I tried today and it worked.

You can try this link: http://www.dimensionengineering.com/DE-SW0XX.htm

[LM317 high voltage]

I'm looking for an alternative to four 22V Zeners. The arguement was that IF a Zener shorted, the rest could also go.

That's not a good argument;

[Convert 0-30V 3A PSU to 5A or more]

Roomi, as audioguru and indulis already said, there is no problem to exchange a large capacitor to some smaller types in parallel.

ESR and parasitic inductance will be lower with a parallel capacitor assembly, but this will not affect its performance (in fact, if this was a switching power supply, it could even improve the performance).

Of course, price and space will be different, but it's better than not assembly the project due to a impossible to find piece.

[voltage reducer]

what can be added on the secondary side of the trafo, possibly near the bulb, to have an alternative supply of reduced voltage available on a toggle switch, so that the lamp can be switched

[converting high range analog voltmeter]

i want use a analog voltmeter that is of 300V range as 15V voltmeter.so can i do this job by making its range near to 15V or nearby. :o

Analog voltmeters have a resistor in series with its coil;

[silicon controlled rectifier]

can we add more n and p junctions in pnpn transistor,if not then why?can we make two bases in pnpn transistor?

A PNPN device is a SCR thyristor, as the title says;

[Convert 0-30V 3A PSU to 5A or more]

But I will not be able to buy on internet from Bangladesh.Is there any alternative ?

Yes.