11 Apr
2012
11 Apr
'12
6:25 a.m.
-----Original Message-----
From: cctalk-bounces at classiccmp.org [mailto:cctalk-
bounces at classiccmp.org] On Behalf Of David Riley
Sent: 11 April 2012 13:15
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Re: Equivalent of an A55 Transistor
On Apr 11, 2012, at 7:29 AM, Chris Elmquist wrote:
Looks like there is an MPSA55 and an MPSA55G. The MPSA55 is a Darlington transistor,
according to Farnell; I recently learned a little about those repairing my RD53 motor
control board, and my understanding is that the gain is even higher with those. Given that
it seems I need less gain than the MPSA55G provides, the straight MPSA55 would seem
unnecessary. However, Farnell will charge me a lot because it has to ship them from the US
to the UK. An Ebay seller here in the UK seems to have the Darlington variety, so I could
get some of those sooner and cheaper. The alternative seems to be an MPS2907AG from
Farnell http://uk.farnell.com/jsp/search/productdetail.jsp?sku=1611212.
What would people advise?
NB This transistor is used to switch in a resistor that controls the timing of a 555 which
drivers the PSU chopper transistor. If anyone wants to look, it is Q21 on p88 (in the PDF)
of the H7140 printset, which is here:
http://bitsavers.org/pdf/dec/pdp11/1124/MP01018_1124schem_Aug80.pdf.
Thanks
Rob
On Wednesday (04/11/2012 at 09:23AM +0100), Rob
Jarratt wrote:
OnSemi makes a lot of older transistors (they still have half the ones needed
to fix a Wurlitzer electric piano). Confusingly, the datasheet title says
"NPN", but everything else says "PNP"; it's probably because the
datasheet
is for both the NPN devices (MPS?05) and the PNP ones.
In any case, that should be a 100% correct replacement; they may be hard to
find in stock abroad. I could only reliably find them at Arrow in the US when
I was fixing my Wurlitzer.
- Dave
I need to replace a transistor in my H7140 PSU
for my PDP11/24. The
transistor is marked GPSA55J3 and the printset identifies it as "XA
55 PNP 500MW SI 60 50 P", it is in a TO-92 package. I have tried to
find specs for an A55 and can only find partial matches, so I am not
sure what today's equivalent would be. Can anyone help me work out
what the equivalent today would be?
MPSA55G?
http://www.onsemi.com/PowerSolutions/product.do?id=MPSA55