Video Amp Circuit Modification

Suraj143 · Dec 3, 2018

I built the below video amp & it worked nicely.But it is One in One out video amp.
https://www.learningelectronics.net/circuits/video-amplifier.html

Now I want One in TWO out Video distributor.I added the red colored capacitor coupled but did not worked.Without the capacitors it is working nicely.

Any Ideas?

Les Jones · Dec 4, 2018

By adding the capacitors you will have lost the DC component of the video signal. It may work with some video equipment if it's input circuit incudes DC restoration.

Les.

Nigel Goodwin · Dec 4, 2018

Also the capacitors are really too small - and probably not needed anyway, the input it's feeding 'should' have DC blocking, but AFTER the 75 ohm load resistor, this allows much smaller capacitors.

Suraj143 · Dec 4, 2018

Hi,

If I remove the output capacitors & by mistake if I short circuit the output to ground will it damage the transistor?

Nigel Goodwin · Dec 4, 2018

No, there's a 75 ohm resistor which limits the current, and in normal use theres two 75 ohms (150 ohms) in series to ground anyway.

Suraj143 · Dec 4, 2018

Nigel Goodwin said:
No, there's a 75 ohm resistor which limits the current, and in normal use theres two 75 ohms (150 ohms) in series to ground anyway.

In my circuit when shorted 5V/75R=66mA current will flow through the transistor.....!!!

Do I need another 75 Resistor ?

Nigel Goodwin · Dec 4, 2018

Suraj143 said:
In my circuit when shorted 5V/75R=66mA current will flow through the transistor.....!!!

Do I need another 75 Resistor ?

No, the other 75 ohm is on the input it's feeding.

There also won't be 5V on the 75 ohm, it will be less than that, dependent on the setting of P1.

unclejed613 · Dec 5, 2018

if you were to use 2N3904/3906 transistors here, the max Ic would be 200mA, so short circuits at the output wouldn't be a problem.

Nigel Goodwin · Dec 5, 2018

unclejed613 said:
if you were to use 2N3904/3906 transistors here, the max Ic would be 200mA, so short circuits at the output wouldn't be a problem.

A BC560 is 100mA, which is plenty more than required, even with a S/C from the output of the 75 ohm.

Video Amp Circuit Modification

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