Film-Tech Forum ARCHIVE: Dolby cat. 123 transistors

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Posted by Miguel Angel Martorell (Member # 1110) on 05-17-2008, 04:55 PM:

Hi every one:

It´s been a long time without posting anything but I keep learning reading all of your posts.
I need a little help. I´ve checked the CP50 manual and there´s a diagram of the Dolby cat 122 card but I can´t find wich are the transistors named Q101, Q102,...,Q104.

Anybody knows wich transistors uses this dolby cards????.

Thanks in advance and sorry for my poor english.

Posted by Mark Gulbrandsen (Member # 72) on 05-17-2008, 08:12 PM:

Your english is actually darn good! I still can't speak proper english either. There should be numbers on the transistors themselves. Perhaps they are of the "BC" series or something similar. Take a look and let us kow. Then its easier to reccomend a good cross match to a currently available device. IN fact the originals may also still be available.

Thanks!

Mark

Posted by Miguel Angel Martorell (Member # 1110) on 05-18-2008, 07:07 AM:

Thanks Mark for your quick answer. My problem is that I don´t have the card here but the guy who has it says that the place where the transistors fit there´s no reference about what kind they are so I keep looking. If there´s any idea...

Thanks and...un saludo desde Valencia.

Posted by Mark Gulbrandsen (Member # 72) on 05-18-2008, 07:58 AM:

I will look at the card when I'm at work tommrrow. If someone here has access today they may be able to help faster though. Otherwise I should be able to tell you tommrrow.

MArk

Posted by Steve Guttag (Member # 268) on 05-18-2008, 12:24 PM:

Cat 122? That is just the simple remote fader box...no transistors in there. Just a 100K pot, LED and current limiting resistor.

The Cat 123, which looks identical from the outside, is the master remote fader and it does have some transistors used for switching control between the "master" and "remote faders based on the "CO Info" signal from the CP50.

It is true that the schematic does not list the transistors but they are being used as simple switches and as such are not too criticial in specification. However, most manufactuers have their "favorite" transistors for this sort of thing...I know I do and will use the same ones (PNP or NPN) for most designs unless some specific requirements come up that require alternate choices.

Dolby traditionally uses BC416s for PNP and BC414 for NPN and those are likely what were used originally. That is definately where I would start.

In the case of the Cat 123, two of each are used. Two are used to drive the LEDs on the remote boxes (one for each) and two are used to switch which fader is active.

Just what isn't working?

Steve

Posted by Miguel Angel Martorell (Member # 1110) on 05-18-2008, 02:40 PM:

Sorry. My mistake!!!!. You are right about the cat. 122. That´s the cat. 123 I´m interested in. Thanks Steve and Mark for your answers.

All works OK or I hope so. This is only homework but thanks a lot for the interest.

Saludos desde Valencia.

Miguel Angel