Re: Question: R7903 Cap Rectifier Board 130v supply


Miroslav Pokorni
 

No, it was not MPS918, I got reference number wrong and from there part
number was wrong, too. The lamp driver that I started from is Q469, generic
number MPS6521, but this one is not a very sturdy device, either. The
continuos collector current is 100 mA, not very much for an incandescent
lamp cold filament surge. The basic device has gain between 150 and 600. I
wonder whether it was higher gain that was selection criteria.

Regards

Miroslav Pokorni

----- Original Message -----
From: "Denton, Adam (Exchange)" <adenton@bear.com>
To: <tekscopes@yahoogroups.com>
Sent: Wednesday, November 05, 2003 9:09 AM
Subject: RE: [TekScopes] Question: R7903 Cap Rectifier Board 130v supply


I find it mind boggling that transistors for driving lamps
are selected from a standard transistor type,
e.g. Q238 in 7904 is selected from MPS918.
Are you serious?!! MPS918 is used as a LAMP DRIVER??!!
My god, MPS918 is a rather delicate RF transistor
(VCEo = 15V, fT = 600MHz, Ic = 50mA). Just about the
LAST part I would ever choose to drive a lamp. Ouch!

To my mind that shows a lack of adult supervision in design
department.
Scary. Did they employ the same lackey in the design of
the now-infamous 24xx U-800? :-O

-Adam

From: Miroslav Pokorni [mailto:mpokorni2000@yahoo.com]
Sent: Friday, October 31, 2003 10:42 PM
To: tekscopes@yahoogroups.com; Joe Sleator
Subject: Re: [TekScopes] Question: R7903 Cap Rectifier Board 130v supply

***********************************************************************
Bear Stearns is not responsible for any recommendation, solicitation,
offer or agreement or any information about any transaction, customer
account or account activity contained in this communication.
***********************************************************************

Join TekScopes@groups.io to automatically receive all group messages.