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_1123…
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.…. 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
--
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