> From: Rob Jarratt
> Does anyone know what the correct one is?
has all the details.
(If anyone knows of any PDP-11 hardware or UNIX information which is not on
the CHWiki - I'm not interested in DEC PDP-11 software, but if someone would
like to take that on, that would be great - please let me know.)
Selectron Vacuum Tube: https://www.ebay.com/itm/174977901251
Really nice photo-shoot! I wonder what the back-story to this particular
tube might be.
I don't think that $16.18 shipping would be, um, adequate protection by any
Cheap, but not so sure about "cost-effective" .
Bill Whitson, the original ClassicCmp ListOp, has a surprisingly little amount of information available about him online. Does anyone know what happened to him after the late 90s? (If anyone has any contact information, that would be nice!)
It would be a lot easier to replace the large circular regulator if you're
taking the shotgun approach, and much more likely that the regulator is a
source of faults. and it's cheaper. For the h744, 45, 54. BUT measuring
things is the best way if you can do it. Pull the values from the
backplane, there are test points that you can measure from.
On Thu, Jan 6, 2022 at 2:30 PM Wayne S via cctech <cctech at classiccmp.org>
> So you want to replace capacitors just because they ?whine? ?
> I?ll say that because you are learning, that is not good troubleshooting
> Make a checklist of troubleshooting power supplies.
> There are a lot of good youtube videos and other internet information on
> how power supplies work, how to check them and repair them. There is danger
> when working with power supplies.
> When working on electrical equipment do you know about the ?working with
> one hand in your pocket rule?? Doing this stuff, videos and reading, is not
> overly time consuming and may save your life!
> Sent from my iPhone
> > On Jan 6, 2022, at 07:50, Jon Elson via cctalk <cctalk at classiccmp.org>
> > ?On 1/6/22 2:52 AM, Rob Jarratt via cctalk wrote:
> >> I think I may need to replace the two output capacitors in some of my
> >> regulators. These are screw terminal 6,000uF 10V parts. I have looked on
> >> Mouser, Farnell and Digikey and there don't seem to be any available,
> >> any that are listed are really rather costly.
> >> Does anyone know where I might find some, preferably from a reputable
> >> supplier. Note that I am in the UK.
> > Mouser is a good place to find big caps (or at least used to be). You
> might have to get "snap in" caps and solder wires to them, that style seems
> to be more available.
> > Jon
On 1/6/22 10:17, William Donzelli wrote:
> If you include prototypes, then you need to include ALL the prototypes
> - even things made in single quantities that never worked.
> That is a HUGE amount of stuff that makes EBAM look gigantic.
To be fair, EBAM received a not-insignificant amount of press coverage.
What doomed it was the falling cost and increasing density of
semiconductor memory. Good idea, wrong time.
It was pitched in a few forward-looking responses to government RFPs.
But then, so was a lot of other stuff.
The starting price is expensive, but probably not utterly unreasonable,
- the 780 was the first VAX, and thus historically important
- 780's are incredibly rare; this is the first one I recall seeing for sale
in the classic computer era (versus several -11/70's, /40s, etc)
- this one appears to be reasonably complete; no idea if all the key CPU
boards are included, but it's things like the backplane, etc (all of which
seem to be there) which would be completely impossible to find now - if any
boards _are_ missing, there's at least the _hope_ that they can be located
(780 boards seem to come by every so often on eBait), since people seem to
keep boards, not realizing that without the other bits they are useless
Anyway I fully expect it to go (because of those, especially i and ii) for a
_lot_ more than the opening price.
I've sent the seller info on the complete 780 board set, and a suggestion
that it's in their own best interest (maximize bidding) to check to see if
> From: Scott Quinn
> I have seen some roads where the utility has 2 of the phases plus
> neutral going down them, not true 2-phase power, but 2 phases 120/240
> degrees apart with the third phase just not present.
My street has that. The subdivision as a whole has all 3 phases (down the
main road through it), but individual streets off of it have only 1 or 2.
(The whole subdivision is on poles, so it's easy to see.) On the ones with 2,
some houses are connected to one, some to the other.
> I guess they figure twice the loads for only one more wire.
No, because most homes are only connected to one phase. I think the main
reason to do it is that it allows the total load (of the entire subdivision)
to be somewhat balanced across all 3 phases.
> Can't remember what it was called but I do remember seeing in some book
> somewhere about a "phantom 3rd leg" or something
My house has something like that; the previous owner wanted '3-phase service'
for machine tools (I think - could have been a compressor, or something) in
his basement workshop, so they sold him a pseudo-3-phase service. I forget
the exact details of how it works, but the 3rd phase is at 170V to neutral,
or something like that. (So I can't power any 110V outlets off the third
I think the way it works is that the two 'main' phases are 220V to each
other, 110V to neutral (I think from the usual center-tapped transformer off
one of the three main feed phases, i.e. 180 degrees to each other). The third
'pase' is generated by a second, smaller transformer connected to the other
feed phase in some arcane way I forget the details of. So it's 120 degrees
away from the other two.
On Sun, 2022-01-02 at 12:00 -0600, Grant wrote:
> Where are you getting two /different/ phases?? --? Remember, the
> different legs on residential 120/240 wiring are really the same
> How do you get *two* /different/ phases without access to a *third*
> phase?? There are only a few places in the U.S.A. (and I'm not aware
> anywhere else in the world) that actually have 2? power (where the ?
> 90? out of phase with each other).
I have seen some roads where the utility has 2 of the phases plus
neutral going down them, not true 2-phase power, but 2 phases 120/240
degrees apart with the third phase just not present. Every time I've
seen that it seems like fools economy, but I guess they figure twice
the loads for only one more wire.
Can't remember what it was called but I do remember seeing in some book
somewhere about a "phantom 3rd leg" or something where they used 2
wires with 120/240 degree phase separation into the transformer and
then the third phase "corner" was just floating and current would
"return" across the other two. As it was brought up in the context of
"make sure some yahoo didn't try this on your install and if they did
be very careful" and was delta-only I imagine it was not that common.
> From: Jon Elson
> It should be 208V
Oh, right you are. It's been a long time, and I had a distinct memory that it
was less than that, but I looked, and I think that's it. The term for my
flavour of 3-phase is apparently "open wye/open delta"; each leg is 240V to
the others, but only two are 110V to neutral - the "hi leg" (normally
colour-coded orange; normal 3-phase uses black/red/blue) is 208V.
The page Jonathan Chapman sent had a good diagram of how it is wired:
When they were doing some work on the pole decades back, I asked the foreman
how it worked, and he drew a diagram to show me; I had forgotten it, but
seeing that, that is it. The A and C are produced off one feed phase, but the
B comes from the second feed phase.