Holm Tiffe via cctalk wrote:
> Robert Jarratt via cctalk wrote:
>
> > I asked this before a few years ago but didn't come to a firm conclusion.
> > The two parts are shown in this picture:
> > https://rjarratt.wordpress.com/wp-content/uploads/2023/12/img_20231221_112305.jpg
> >
> > They are from a VT100 Monitor board. There is no schematic for my version
> > of the board, but a related schematic is on p58 of this schematic:
> > https://bitsavers.org/pdf/dec/terminal/vt100/MP00633_VT100_Schematic_Feb82.pdf.
> > They are labelled Q414 and CR406, but the Feb 82 revision uses a different
> > board and those two parts are in TO-220 packages rather than TO-3 as here..
> >
> > I have removed both of them and tested them with a DMM. Neither of them
> > measure as two diodes, they do not measure open circuit in any direction,
> > so either they are both faulty or they are not transistors (unlikely). I
> > have found a spec for a 2SB411 at
> > https://alltransistors.com/transistor.php?transistor=10279. This seems to
> > be a germanium transistor. When I last asked about this I had a
> > conversation with Tony Duell, who was very sceptical that these could be
> > germanium transistors, so naturally I am very doubtful that they are 2SB411
> > transistors. However, in the schematic Q414 is shown as NPN, the 2SB411 is
> > PNP and this seems to match the way the part is connected on my board
> > (Collector to HORIZ GND). I am working on a reverse engineered schematic.
> >
> > Can anyone tell me what these components are so I can find a datasheet for
> > them? Better still a suggested replacement would be really helpful,
> > especially if they are 2SB411s because they seem to be hard to find.
> >
> > Thanks
> >
> > Rob
>
>
> I don't think that it where a bigger problem to change them against
> similar powerful TO220 PNPs. The cooling isn't existent or only has a
> small heat sink so that the allowed 40W power loss arent used anyways.
> TO220 Transistors fit easyly on TO3 Footprints.
>
> Regards,
> Holm
>
> --
An old friend of mine wrote me a mail, since his mails to cctalk seems
to go to nowhere andsuggested to forward (and translate) this
In the bitsaver schematic Q414 is a fat BU407 power transistor and must
be, since it has to resist high inductive voltage spikes, there for the
inverse diode.
He thinks that the transistor is a RCA411 and no 2SB ..it would fit
better there. Probably ore cheap would be a BU407 (reichelt.de 95 cent).
I would use an BU508D in TO247 / TOP3P housing, it contains the revere
diode.. but none of them is PNP...
Regards,
Holm
--
Technik Service u. Handel Tiffe, www.tsht.de, Holm Tiffe,
Goethestrasse 15, 09569 Oederan, USt-Id: DE253710583
[email protected] Tel +49 37292 709778 Mobil: 0172 8790 741
