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.


Miroslav Pokorni

----- Original Message -----
From: "Denton, Adam (Exchange)" <>
To: <>
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
Scary. Did they employ the same lackey in the design of
the now-infamous 24xx U-800? :-O


From: Miroslav Pokorni []
Sent: Friday, October 31, 2003 10:42 PM
To:; Joe Sleator
Subject: Re: [TekScopes] Question: R7903 Cap Rectifier Board 130v supply

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