31 Mar
2009
31 Mar
'09
12:33 p.m.
I've just started the rebuild of one of my PDP-8/Ms. This is an early
machine with the power supply mounted on the left of the chassis.
One potential problem I am slightly concerned about is that the front
two power transistors have been desoldered and removed. Does anyone know
if these are a vital part of the PSU and if so what the part numbers are
so I can try to source replacements?
You can see a picture here http://www.pdp8.co.uk/ (enlarged view here
http://www.pdp8.co.uk/files/2009/03/00016.jpg)
If anyone else has a PSU of this type, could they take the opportunity
to take a few pictures for me. Would be really useful to have another
reference source for the rebuild.
All the best,
Toby
--
This message has been scanned for viruses and
dangerous content by MailScanner, and is
believed to be clean.
6 Apr
6 Apr
12:18 p.m.
I've managed to find out a little more about the two missing components
on my PDP-8/Ms power supply and alas they look most vital!
One is a DEC 1110714 bridge rectifier and the other is a MJ900
transistor. I think I've sourced the MJ900 but can't find anywhere
stocking the 1110714.
Does anyone know an alternative non-DEC part number for the rectifier?
Many thanks,
Toby
On Tue, 2009-03-31 at 20:33 +0100, Tobias Russell wrote:
I've just started the rebuild of one of my
PDP-8/Ms. This is an early
machine with the power supply mounted on the left of the chassis.
One potential problem I am slightly concerned about is that the front
two power transistors have been desoldered and removed. Does anyone know
if these are a vital part of the PSU and if so what the part numbers are
so I can try to source replacements?
You can see a picture here http://www.pdp8.co.uk/ (enlarged view here
http://www.pdp8.co.uk/files/2009/03/00016.jpg)
If anyone else has a PSU of this type, could they take the opportunity
to take a few pictures for me. Would be really useful to have another
reference source for the rebuild.
All the best,
Toby
--
This message has been scanned for viruses and
dangerous content by MailScanner, and is
believed to be clean.
1 p.m.
One is a DEC 1110714 bridge rectifier and the other is
a MJ900
transistor. I think I've sourced the MJ900 but can't find anywhere
stocking the 1110714.
Does anyone know an alternative non-DEC part number for the rectifier?
Are you sure it's a _bridge_ rectifier? I thought you said it was a TO3
can, DEC often used a double-diode in that case (common cathode to the
case, anode to the 2 pins -- sort of a semiconductor version of an EZ80
:-)) as a biphase full-wave rectifier with a centre-tapped transformer
winding.
In any case it should be fairly easy to get some diodes with sufficient
forward courrent capacity (and enough PIV -- rememebr this is _twice_ the
peak voltag from the transformer!) to do the job and just wire them up
appropritately. There should be enough spave in a PDP8/M PSU to fit them
in. It may not look original, but it'll get the machine going and you can
always fit the original part if you find one.
-tony
1:59 p.m.
Thanks Tony,
Yes pretty sure its a bridge rectifier as I found H740 schematics plus
opened up my other 8-M which I now realise has essentially the same
power supply. I guess DEC just made slight design revisions plus
reposition the supply in order to solve the unreliability of these
earlier units.
Studying the schematic further I've found NSS-3514 annotated next to the
rectifier (sorry missed this when I first looked through it) so I'll see
if I can hunt down this part. If not I'll try the diode approach
Thanks,
Toby
On Mon, 2009-04-06 at 21:00 +0100, Tony Duell wrote:
--
This message has been scanned for viruses and
dangerous content by MailScanner, and is
believed to be clean.
One is a DEC
1110714 bridge rectifier and the other is a MJ900
transistor. I think I've sourced the MJ900 but can't find anywhere
stocking the 1110714.
Does anyone know an alternative non-DEC part number for the rectifier?
Are you sure it's a _bridge_ rectifier? I thought you said it was a TO3
can, DEC often used a double-diode in that case (common cathode to the
case, anode to the 2 pins -- sort of a semiconductor version of an EZ80
:-)) as a biphase full-wave rectifier with a centre-tapped transformer
winding.
In any case it should be fairly easy to get some diodes with sufficient
forward courrent capacity (and enough PIV -- rememebr this is _twice_ the
peak voltag from the transformer!) to do the job and just wire them up
appropritately. There should be enough spave in a PDP8/M PSU to fit them
in. It may not look original, but it'll get the machine going and you can
always fit the original part if you find one.
-tony
8:24 p.m.
I think the regulator is a 54-09728 or 54-09827, and they were used ia lot
of DEC items.
Paul
On Mon, Apr 6, 2009 at 3:59 PM, Tobias Russell <toby at coreware.co.uk> wrote:
Thanks Tony,
Yes pretty sure its a bridge rectifier as I found H740 schematics plus
opened up my other 8-M which I now realise has essentially the same
power supply. I guess DEC just made slight design revisions plus
reposition the supply in order to solve the unreliability of these
earlier units.
Studying the schematic further I've found NSS-3514 annotated next to the
rectifier (sorry missed this when I first looked through it) so I'll see
if I can hunt down this part. If not I'll try the diode approach
Thanks,
Toby
On Mon, 2009-04-06 at 21:00 +0100, Tony Duell wrote:
--
This message has been scanned for viruses and
dangerous content by MailScanner, and is
believed to be clean.
One is a
DEC 1110714 bridge rectifier and the other is a MJ900
transistor. I think I've sourced the MJ900 but can't find anywhere
stocking the 1110714.
Does anyone know an alternative non-DEC part number for the rectifier?
Are you sure it's a _bridge_ rectifier? I thought you said it was a TO3
can, DEC often used a double-diode in that case (common cathode to the
case, anode to the 2 pins -- sort of a semiconductor version of an EZ80
:-)) as a biphase full-wave rectifier with a centre-tapped transformer
winding.
In any case it should be fairly easy to get some diodes with sufficient
forward courrent capacity (and enough PIV -- rememebr this is _twice_ the
peak voltag from the transformer!) to do the job and just wire them up
appropritately. There should be enough spave in a PDP8/M PSU to fit them
in. It may not look original, but it'll get the machine going and you can
always fit the original part if you find one.
-tony
7 Apr
7 Apr
12:52 p.m.
Thanks Tony,
Yes pretty sure its a bridge rectifier as I found H740 schematics plus
OK...
Bridge rectifiers are not exactly critical components. Provided they'll
pass enough current amd stand sufficient inverse voltage, they'll work.
It shouldn't be hard to estimate those (for the latter, 3 times the
transformer voltage (or strictly 2 * sqrt(2) * transformer voltage) will
do.
There will be something avaialbel that will work.
-tony
5743
days inactive
5750
days old
5 comments
3 participants
participants (3)
-
ard＠p850ug1.demon.co.uk -
toby＠coreware.co.uk -
useddec＠gmail.com