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Dec PC04 light bulb

Roland Huisman

Roland Huisman

Veteran Member
Joined
Mar 24, 2011
Messages
1,464
Location
The Netherlands
Hello everyone,

This PC04 came with my recently acquired PDP8/e (pics and story will come soon).
I've done a bit research on the web before I got the machine. In the articles that
I found I've seen some sort of car tube lamp. In this PC04 Dec used some sort
of flashlight bulb... In the front of the lamp is a small lens.

Does anyone know a replacement for this lamp? I've never seen such a light bulb.
The lamp is still good but its filament is a little bit aged. (You can see a same sort
of aging symptom as halogen lamps have)

01 pc04.jpg 02 pc04.jpg 03 pc04.jpg 04 pc04.jpg 05 pc04.jpg


Regards, Roland
 
Is the lamp inside the lens part, or is the lens an integral part of the envelope of the lamp? If the latter, I have never seen something like that, except for penlight bulbs, but they usually have a rounded lens at the end of about 3/16" diameter.

Lou
 
All of the documentation and pictures that I can find for the PC04/PC05 show the "car" light bulb for the reader.
Maybe your PC04 was modified?
 
@ Lou,

Yes, the lens is an integral part of the envelope of the lamp.
There is also a number on the back of the lamp: WA999056
You can only replace the whole lamp as seen on the picture.
The metal part is glued on the lamp.

@ m_thompson,

You are probably right about a modification. Maybe this lamp is from
an other model papertape reader. But why? These car lamps
were not really special in those days...

Here is a close up from the lamp. It really fits in a right way.
But you can also see a conical hole for a original lamp.

PC04 lens.jpg

I think I have to keep it this way because I have no idea
where to get the original lens. This seems to be the original way:

original way.jpg

Regards, Roland
 
Last edited:
A little progress has been made on the PC04. The puncher
part was stuck and it was not possible to turn the motor.
So I took the motor apart to clean it. The first thing which I noticed
were a few cut off fan blades. This was done to balance the rotor.

01 cheap balancing.jpg

The General Electrics motor has a plain bearing instead of ball bearing.
The oil has been dried out after many years. This is why the motor gets stuck.
After removing the dried oil it is necessary to fill the filt with oil. This filt touches
the motor axis to oil it constantly while it is running.

02 plain bearing oil filt.jpg

These motors have two oil filling points. There is a small hole at the front and
back of the motor. But to reach them you need to take out the motor from the PC04.
These points are behind the yellow arrow in the picture. It's really important to
oil the motor, otherwise you will kill your plain bearing.

03 oil point.jpg


And of course the punch mechanics was stuck too. I oiled the moving
parts (except the punch needles) and waited a few days to let the oil get in.

And now I can punch papertapes with the PDP8. :D I have the test program
running on the PDP8/e to just generate random characters.

https://youtu.be/nzVyNVktes8


So now the reader part can be tested because I didn't had any punched paper.
When the PC04 is fully working again, I will put in the Arduino PCB from Mattis.
Then I can also punch papertapes from a modern PC.

Regards, Roland
 
Roland Huisman said:
View attachment 23950
Click to expand...

That capacitor is likely to contain PCB, depending on when it is manufactured. I have replaced that one in mine with 7.5uF 370VAC capacitors from Cornell-Dublier, just in case.

Here is a photo of my reader assembly. Not very sharp unfortunately:

2EXyVDS.jpg


It looks identical to yours. (although much more dusty)

Good luck with the reader/punch PCB!
 
Hello Mattis,

Your lamp construction looks identical to mine indeed!
So it is probably original or a modification from DEC... Interesting!
I wonder, is your PC04 also built early 1971?

About that capacitor... I think you are right about the PCB risk.
Maybe it is a good idea to replace it. Although it doesn't show
leakage and it is electrically in good shape.

Regards, Roland
 
Roland Huisman said:
Hello Mattis,

Your lamp construction looks identical to mine indeed!
So it is probably original or a modification from DEC... Interesting!
I wonder, is your PC04 also built early 1971?

About that capacitor... I think you are right about the PCB risk.
Maybe it is a good idea to replace it. Although it doesn't show
leakage and it is electrically in good shape.

Regards, Roland
Click to expand...

This one is from around 1973. But I have older ones as well. For the 8/L machines. And a reader only. And then one for the PDP-9 (not technically a PC04). All of them a fairly similar in terms of construction. The PC05 I have is fairly modern, late seventies or early eighties. I'll check them this weekend.
 
Hi Roland, I thought I would take a look at the bulb in my PC04, just to compare, and it is indeed the same set up as your lamp assembly, pic. shows detail
.....Harry
 

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I finally decided to peek at this thread. That lamp looks awfully familiar--according to my memory, it was most commonly used as a panel indicator. What power is applied to it--in particular, AC or DC? It could well be that a modern LED "bi-pin" replacement could be made to fit like a glove.
 
@Harry

Oh thanks! More and more of them are showing up now :D

@Chuck

Well this lamp is quite BIG for just a panel lamp. The lamp is at the 5VDC supply
with a series resistor. The current is 650mA and across the lamp is a voltage of 3.9V


I wonder, would this modification have something to do with the sensitivety for ambient light?

Regards, Roland
 
Roland, that doesn't look that big to me for the time. I suspect that the diameter of the threaded portion is probably in the range of about a centimeter--very typical. Some of the larger panel lamps with jeweled lenses were about 2.5 cm. in diameter.

The resistor undoubtedly extends the life of what is probably a 6.3V lamp and concentrates the spectrum in the near-infrared region.

I wonder that if a period Dialite catalog could be located, that you might see it in there (or something very close).
 
Chuck(G) said:
Roland, that doesn't look that big to me for the time. I suspect that the diameter of the threaded portion is probably in the range of about a centimeter--very typical. Some of the larger panel lamps with jeweled lenses were about 2.5 cm. in diameter.

The resistor undoubtedly extends the life of what is probably a 6.3V lamp and concentrates the spectrum in the near-infrared region.

I wonder that if a period Dialite catalog could be located, that you might see it in there (or something very close).
Click to expand...

Ah yes, now I know which panel lamps you mean. Yeah the bulb is about that size.
The only special thing on the bulb is the small lens in the front. But I can't imagine that this
lamp was a special designed lamp for DEC... I hope someone has a seventies Dialite catalog here :D

Regards, Roland
 
jackrubin said:
Are these units all Galway manufacture? Maybe the "festoon" bulb used in US domestic units wasn't available overseas (relative term, of course).

Jack
Click to expand...

Is there a way to tell where a unit is manufactured? The serial number plate says "Maynard Massachusetts". The serial number is 7101. BTW I was probably wrong about the manufacturing year. Some chips inside are dated 7115 so it is maybe a -71 or -72 unit.

I checked the PC02 in the PDP-9. It has the "festoon" bulb. Same for the two PC04 for the PDP-8/L systems. The other PC04 (for the PDP8/a) have the same type of lamp assembly as my first one and the one Roland has. I forgot to check the PC05.
 
I had thought items manufactured in Galway would say "Galway Ireland" instead of "Maynard Massachusetts" but I'm not sure - I think it might be worth a more general query to the group, so I'll start a new thread.

Jack
 
Take a look at the PDP-8/e DEC-O-LOG. ECO 7006247 says:

JUN-74 CORRECTION: Phase-in use of fiber optics light source #12-11722-00 in place of Osram bulb source.
Retrofit all PC04/PC05 if present Osram light source is difficult to align or if unit exhibits marginal operation.
 
m_thompson said:
Take a look at the PDP-8/e DEC-O-LOG. ECO 7006247 says:

JUN-74 CORRECTION: Phase-in use of fiber optics light source #12-11722-00 in place of Osram bulb source.
Retrofit all PC04/PC05 if present Osram light source is difficult to align or if unit exhibits marginal operation.
Click to expand...

The smoking gun ... great detective work!
 
m_thompson said:
Take a look at the PDP-8/e DEC-O-LOG. ECO 7006247 says:

JUN-74 CORRECTION: Phase-in use of fiber optics light source #12-11722-00 in place of Osram bulb source.
Retrofit all PC04/PC05 if present Osram light source is difficult to align or if unit exhibits marginal operation.
Click to expand...

Oh wonderful! Very nice search work! So the inside of the unit is glass fiber.
Nice to know it was an original upgrade. (And is has to be according the amount
of modified units we have seen here...)

Regards, Roland
 
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