23 Mar
2005
23 Mar
'05
12:54 p.m.
>>>> "vrs" == vrs <vrs at
msn.com> writes:
> I am currently modifying my Teletype ASR33 into a
LT33 according
> to the
vrs> DEC
> specifications to work with my PDP-8/L. Does
someone know what is
> a Thyractor (GE 6RS20SP4B4) ? Some kind of voltage clamping device
> ?. How could I make one, using, for instance a pair of thyristors
> or a pair
vrs> of
> zenner diodes ?
vrs> thyractor: "A marketing name by DAVIS, the thyractor was a
vrs> combination of a low loss choke (the reactor) and a thyristor."
vrs> I know NTE still markets a replacement for the 6RS20SP5B5 (but
vrs> not the 4B4). Unfortunately, I don't have the detailed specs
vrs> for the 4B4.
vrs> On the other hand, I think it is just a handy voltage clamp to
vrs> keep the semiconductor circuits from seeing the inductive spikes
vrs> from the TTY. Shouldn't be too hard to come up with something
vrs> else that would work.
If it's a voltage clamp, then either back to back zeners, or a MOV
should work. MOV might be the better choice since they are explicitly
designed as protective devices. Zeners would be ok in the larger
sizes, but the small ones may be fragile enough that they don't do
well in this application.
paul
24 Mar
24 Mar
2:41 a.m.
New subject: "Thyractors" on the DEC LT33 modified ASR33 Teletype
On Wed, 23 Mar 2005 12:54:35 -0500, Paul Koning <pkoning at equallogic.com> wrote:
If it's a voltage clamp, then either back to back
zeners, or a MOV
should work. MOV might be the better choice since they are explicitly
designed as protective devices. Zeners would be ok in the larger
sizes, but the small ones may be fragile enough that they don't do
well in this application.
I agree. MOVs are designed to be dirt-easy and robust to boot. If I
were to do it, I'd parallel a couple of 5W zeners BEHIND a suitably
sized MOV just to be on the safe side.
/wai-sun
3:45 a.m.
New subject: "Thyractors" on the DEC LT33 modified ASR33 Teletype
----- Original Message -----
From: "Wai-Sun Chia" <waisun.chia at gmail.com>
To: "General Discussion: On-Topic and Off-Topic Posts"
<cctalk at classiccmp.org>
Sent: Thursday, March 24, 2005 7:41 PM
Subject: Re: "Thyractors" on the DEC LT33 modified ASR33 Teletype
On Wed, 23 Mar 2005 12:54:35 -0500, Paul Koning
<pkoning at equallogic.com> wrote:
Seems to be not well known that MOVs die - slowly but inevitably -
with use. Every time they shunt a surge, they shorten their useful
life. The harder they work, the shorter their life. If they are known
to be earning their keep, they should be routinely replaced to
maintain the required/designed protection level.
For a low power application like this I'd be inclined to use
back-to-back (in series opposing) zeners with suitable ratings. Make
'em big enuff and they'll last forever.
DaveB, NZ
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If it's a voltage clamp, then either back to
back zeners, or a MOV
should work. MOV might be the better choice since they are
explicitly
designed as protective devices. Zeners would be ok in the larger
sizes, but the small ones may be fragile enough that they don't do
well in this application.
I agree. MOVs are designed to be dirt-easy and robust to boot. If I
were to do it, I'd parallel a couple of 5W zeners BEHIND a suitably
sized MOV just to be on the safe side.
/wai-sun 
25 Mar
25 Mar
12:18 a.m.
New subject: PDP 8/e Front Panel Lamp Replacement
Hi, all,
While I've been tinkering with the PDP 8/e I just took out of storage,
I've found that a couple of the front panel bulbs are burned out.
I know that this has been discussed here before, but does anyone have
a clue where I can get replacements that will work?
I understand that the bulbs are type T1, 14V @ 0.40A, with .125 pin
spacing, and 0.75 tall. I have a DEC part number, but, of course, that
today is useless. I've searched around the net some, but can't find
anything like that.
I've worked around it by taking the bulbs from the extended address page
lights and using them as replacements, but I'd like to get all the lights
working again. At least now the 12 address and 12 "status" lights, along
with
the "RUN" light work.
Any help appreciated.
Thanks,
Rick Bensene
P.S., I don't want to switch it over to LED's or anything like that, I want
to keep
it as original as I can.
12:40 a.m.
New subject: PDP 8/e Front Panel Lamp Replacement
While I've been tinkering with the PDP 8/e I just
took out of storage,
I've found that a couple of the front panel bulbs are burned out.
I know that this has been discussed here before, but does anyone have
a clue where I can get replacements that will work?
Some people have had some luck with my page:
http://mysite.verizon.net/res1ac3j/id9.html
I understand that the bulbs are type T1, 14V @ 0.40A,
with .125 pin
spacing, and 0.75 tall. I have a DEC part number, but, of course, that
today is useless. I've searched around the net some, but can't find
anything like that.
I don't think that is the correct voltage for an 8/e bulb, though it is
about right for an 8/i bulb. I believe the 8/e uses 10V bulbs, though many
seem to have been rlamped with 8/i bulbs, for some reason. (Perhaps the
dimmer presentation was acceptable, and the higher voltage bulbs lasted
longer?)
I believe the original 8/e bulb was equivalent to the CM2309. Those are not
easy to find these days, but the CM7371 are readily available, and should
work OK (and have a longer lifespan, too).
(The 8/e lamps are already socketed, so you lucked out there.)
Vince
7036
days inactive
7038
days old
4 comments
5 participants
participants (5)
-
pkoning＠equallogic.com -
rickb＠bensene.com -
tractorb＠ihug.co.nz -
vrs＠msn.com -
waisun.chia＠gmail.com