[considerations in replacing transistors???]

what parameters do I need consider in replacing transistors?

my idea... please tell me if i'm wrong

Vceo must be greater than or equal than the original.
Ic must be greater than or equal than the original
Power dissipation must be greater than or equal than the original.
Frequency range -- no idea >.< does it matter in DC operation?
Beta range - does it need to be exact?

any other parameters to be considered?

[Cutoff frequency and 3dB points]

Hi All,
I may not be 100% correct,but,a loss of 3db in gain does not hamper the overall response of the amplifier.i.e this loss is unnoticable in the o/p of amplifier.But we get higher bandwidth at peak- 3db gain,compared to bandwidth obtained considering only the flat portion of the gain-frequency plot.
I would like someone to give more explanation of it.

At -3dB the output power is half the midband power output. ( Yes it's noticable )

[Quick questions about transformers]

I found a site for calculating filter capacitor values...

http://my.integritynet.com.au/purdic/power1.html

If we accept the 2.5% ripple as adequate for our purposes then at 13V this becomes 13 * 0.025 = 0.325 Vrms.  The peak to peak value is 2.828 times this value. Vrip = 0.325V X 2.828 = 0.92 V and this value is required to calculate the value of C1. Also required for this calculation is the time interval for charging pulses. If you are on a 60Hz system it it 1/ (2 * 60 ) = 0.008333 which is 8.33 milliseconds. For a 50Hz system it is 0.01 sec or 10 milliseconds.

The formula for C1 is:
C1 (uF) = [ ( IL * t )  / Vrip ] X 106

So for my 24V 12A...

C1 = [ ( 12A X 0.00833 ) / 1.6968V ] X 10^6
C1 = 58910.89 uF  :o ??? :o ???

Plausible?

[Cutoff frequency and 3dB points]

In the Bode plot:

Cutoff frequency ( lower or upper ) are the frequency wherein the midrange gain is 3dB less.

[Quick questions about transformers]

I just bought a transformer; multi-tapped 0-6-12-24, 12 Amp.

Does it mean it can go up to the max 24 volts rms - 12 Amp ???

What's the min filter capactior value if used as a dc power supply?

( big capactors are expensive >.< )

Some transformers are rated in VA, what does it mean?

[Comment about this design...]

Will it work for 3A?

and... ( from the site )

"NOTE: &nbspR2 is determined by the voltage across the 220 uF Cap.

        (Volts - 1.2)
R2 = -------------
          .015

Any Resistor close to the calculated value should be fine. Its only purpose is for an approximate 15 mA current flow which will create a quite stable -1.2 volt supply. "

does it mean voltage across the cap of the complete circuit?

[Comment about this design...]

http://www3.telus.net/chemelec/Projects/Power-Supply/Power-Supply.htm

schematics:


will it work?