Summer 2016 check-in

I’m just surfacing for a moment because I realize it’s been over 3 months without a post, which is just plain unacceptable.

HOPE XI just wrapped up, and I was there for at least a part of each of the three days – never really staying for the late stuff, but managed to catch at least 4 – 6 talks per day.  The highlight was (as it was two years ago) Deviant Ollan & Howard Payne’s tag-team talk.  This year was about the often abysmal state of physical security, manifested through commonly keyed locks.  Their last HOPE talk was on Elevator Hacking, and the subject of keys was one of it’s focal-points.  I highly recommend checking out the Elevator talk on YouTube.

Other highlights this year included:

I’ve started playing around with Collective Access – an open-source Collection Management System geared towards museums, libraries, and other archival institutions.  I found it after searching in vain for a WordPress solution for digitally curating the collection I present here.  I’ve got about a dozen objects added so far as I learn how it works and tailor it to my needs.  There is an underlying structure that makes it well suited for museum collections, but it’s highly configurable through the web interface;  Vocabulary, relationships, meta-data, object hierarchies, and user-interfaces can be customized without touching a line of code.
It’ll be a few more weeks until I’m comfortable enough with my schema, and I may start to post about my progress.

While at HOPE, I caught up with Evan of the Mid Atlantic Chapter of the Vintage Computer Federation, who (among other things) gave an interesting talk on his work researching early computers.  I’ve got the beginnings of an idea to use Collective Access to help them catalog their impressive inventory.  There are some real gems there, and beyond just cataloging, I’d love an opportunity to take some glamor shots.

The 514 is slowly coming to life – The +225v supply isn’t regulating to full voltage, and I’ve narrowed the problem down to something on the upper deck (the input, vertical amplifier, and calibrator).  With that disconnected, I get a nice, sharp, swept trace.

swept trace w/ upper deck disconnected

swept trace w/ upper deck disconnected

Sorry for the extended black-out, more to come!

Don’t desolider angry

desoldering DIPs with an iron, wick, and a sucker is about the most annoying thing a man can do with his precious time on this earth.  The frustration has probably chipped away days off my life, so there’s now a Hakko FR300 de-soldering iron on its way to me.

RIP DC508A, you never really had a chance.

On the plus side, there’s now one more working DC508A display available.

Canned air, your troubleshooting friend

After being on for about an hour, the intensity dropped to zero again.  After that I’d fire it up, and it would come on but quickly dim, and the intensity control wouldn’t effect the intensity, but move the beam slightly.

I traced the problem to the -15v supply, and finally the capacitor C143 (which I’d already replaced!).  I zeroed in on the problem by cooling areas using canned air with the bottle tilted to get a blast of frost.   The -15v supply would dip down to about 10v shortly after power up, but would rocket back up to -15v when I hit it with the frost, and I’d see the beam change.  A handy trick! With a fresh 10µF in it’s place, and it seems to be working for now.  I did need to hit the CRT bias trimpot to get the beam to extinguish with the intensity control fully counterclockwise.

TU-75B Wattmeter repair

As mentioned in my earlier post, the glass face had broken loose in the wattmeter on my TU-75B Variac.  I managed to re-attach the glass, learn a bit about this particular meter movement, and take a few nice shots while I had the unit apart.

First order of business was to clean out the gasketing material that originally held the glass in place.  It was black and brittle and not too terrible to scrape out of the inside of the meter body.  <sidenote> I do need to get a better understanding of what these original materials are – a table of common materials and finishes of the era, along with how to clean them and affix them would be a great resource to develop </sidenote>


With the inside cleaned, the glass seated flush against the back of the opening.  I scratched up the inside wall a bit with the exacto knife, but it’s not visible when the meter is assembled.


I picked up some Permatex 81730 glass sealant, which was recommended in this post about re-seating vacuum tube bases.  This video about re-seating CRT socket bases was where I first heard about it while researching how to reconnect the base on my OS-8/CU scope.  I figured I’d use it for this application as well, since it’s a similar plastic to glass connection (albeit without the heat of a CRT).  It was a little difficult to work with for this particular application; I wish it was a little more viscous and a little less sticky.  I also have some Permatex 80008 Form-a-Gasket sealant, which perhaps I’ll try next time.  The other gauge I have to re-face is going to be done with acrylic, so that that may be a different type of adhesive.  I was very conservative in applying the permatex, since it was easy to spread to visible parts of the glass and difficult to clean up while it was setting.



With the glass face out of the way, I figured I’d get a few good macro shots of the innards.  The white bobbin on the top is a resistor, while I believe the brass stock in the back is a shunt.



Here’s a closer look at the wire wound resistor.  DSC_0146

And the super fine wire from the V+ connection

The way this meter is able to display wattage is by multiplying voltage by current.  It does this by way of nested coils:  one stationary and one on the movement.  Here is shown the meter at rest.

here is the meter at half way, notice the inner bobbin is rotated.


A few close-ups of the movement





So then I re-installed the meter face and gave it a quick, damp wipe down.  Big Mistake.  See the streaks I’ve caused?  Sigh.. live and learn.  It was a stupid, ham-fisted move on my part.


I also scratched up the glass a bit while I was removing the gasket from it’s face, but it’s not as noticeable  Here’s the finished product.  It seems to have a lot of momentum and/or friction to overcome, and as such doesn’t land on an accurate value when slowly incrementing the voltage.  I’ve only experimented with my 100w desk lamp, but it seems I can only get an accurate reading if I switch from off to full line voltage.  Alternately, it’s just out of cal (which seems odd, as there’s nothing to calibrate) and the over-swing just happens to land the needle on the right number.


I took a picture with the meter against a ruler and some graph paper so I could recreate the next one.  Why I didn’t just trace it is beyond me.


Continued adventures in nixie counting

Getting the Transistor Specialties 1519 back on the bench for some overdue continued exploration.

I’ve found that I can get the ‘B’ channel to increment it’s count by toggling the gate Start/Stop switch.  It’s a center return switch, and only by running the switch all the way from Stop to Start, across the center detent, can I get it to increment.

Some further discoveries:
this toggle trick only works around 110v line voltage.  I’m running it on a vairac, limiting it to 115v.
Earlier I think remarked that it was either 3 different flavors of boards, then I realized it might only be two?  It’s three.  The first counter card is different.  Though the layout is largely the same, some components are different, and it dawned on me only now that it’s probably because that card is the one’s counter, and thus needs to have a much higher bandwidth than those following it.  duh.

Here’s the beginnings of a schematic for the input card (one of two) ignore the ‘trigger level controls’ note.


Variac on Steroids: Tektronix TU-75B

IMG_4651.JPGEvery bench needs a a good Variac.  Until I found this piece, my daily use variac was a 60’s era Radio Shack unit cobbled onto some ply with a JBox on the count of missing the original cord and socket.


It works fine, though only rated for 5 amps and gets a little warm with loads well below that.

The Tektronix TU-75B was apparently designed and built primarily as an in-house device to aid in final testing & adjustment of scopes on their way out the door.  I’ve yet to find documentation on it, and the only other photos I’ve seen show similarly low serial numbers, so I suspect these weren’t made in large numbers.  When I saw it on eBay, I couldn’t resist.

The simplest of Variacs just have a knob to adjust the voltage.  Some of the nicer ones also have a voltmeter and/or ammeter.  This unit has a voltmeter, a wattmeter, and selectable ballasts, in the form of 3 light bulbs (more on this later)

There were a few problems noted in the listing, and a few that weren’t.  One meter is missing it’s glass, and the other’s glass is loose.  I’ve got tape on the wattmeter’s glass face to pull it forward and keep it from interfering with the needle.  I’m going to pick up some Permetex glass sealer for the job, which is also apparently what you should use to re-seat the glass envelope of tubes & CRTs in their socket bases.  I’m also going to laser cut some acrylic to replace the missing face.

The voltmeter’s needle is a little bent up, but it seems to move OK.


The other glaring error was that the brush on the variac wasn’t making contact with the winding.  Super simple fix:  I just had to loosen the rotor and move it closer on the shaft until the brush made contact.  Here it is after the fix. IMG_4657.JPG

There’s also a fuse holder, that appears to be a mod of some sort:IMG_4666.JPG

I like the spare fuse holder.  Note that the tektronix part numbers written in.  The knob that the fuses are connected is the wattmeter multiplier, which appears to be a very low resistance rheostat.  With this mod the knob not only controls the range of the meter, but which fuse is in-line.

I’m a little fuzzy on how the transformer is wired.  Perhaps it’s set up as a series of shunts for the wattmeter?  I’ll have to draw this all out if I can’t find a schematic.

Speaking of the wattmeter,  it’s a 4 terminal device, with separate connections for voltage & amperage, which I guess makes sense; if the voltage was constant, you could get away with just measuring the current, but since the voltage is variable, you have to take both into account.  So how does this meter work?  Does it mechanically multiply the two?  A gentleman on this post confirms my suspicion:

“If this is basically an analog meter using two coils to perform the required instantaneous multiplication, then the voltage coil is connected to the needle, moves, is a high resistance, and probably has a series resistor to scale the voltage, and the fixed coil that the moving coil interacts with is the current coil. If no external current transformer is used, then there is a basic current rating of the current coil relating to the full scale power rating of the meter.

“Basic Electrical Measurements”, by Melville B Stout, 1950, Prentice-Hall.
Look up Indicating instruments – electrodynamometer movement – 418 – 423, and 442 – 450.


Looks like there was an… electrical incident at some point; the leads on the power switch have felt the wrath of some poor fellow’s mistake.  The connections appear to be solid, so I may just slowly back away.   I’d hate to disturb that beautiful wire-loom.


When I snugged brush back up against the winding, the inner contacts (which is a brass pad pushing against a brass plate) make a horrible squeak.  I tried everything I could to eliminate this sound to no avail.  The squeak happens right around 90 – 110 volts, so I’ve rationalized this as an audible alarm that you’re approaching full line-voltage, which is actually quite handy.  Go Tektronix.

I’ll cover the ballasts in another post, but short answer: They’re light-bulbs that you can switch in in series to limit the current.  It’s an old trick, but nice to have it all built in one nice enclosure.

519 Graticule


This gallery contains 5 photos.

Some quick shots of it lit up   Cranked up to full brightness for a few seconds, just to see the leading edge of the pulse.  Don’t do this for long or often.

Tektronix 519 Graticule

Today I finally got schooled on how to use the laser in the model shop.  Frau_Farbissina_laser

As mentioned in a previous post, I drew up the graticule for my Tektronix 519 as a DWG for this laser intro.

The basic workflow is:

  1. make a DWG, using colors to represent different laser attributes (power, speed)
  2. Power up the laser, and use bed Z control and spacer stick to focus
  3. open the file in AutoCAD Trueview(?)
  4. Print to laser driver, which opens up driver app
  5. load the medium
  6. assign colors to laser attributes
  7. drag the print file onto the print area
  8. a few other things
  9. hit go

We used 1/8″ clear cast acrylic.  I don’t remember what the cutting power was, but the engraving setting was power of 8, speed of 1.  Keeping the power the same & halving the speed would result in a deeper cut.

We made two, just for kicks, and they turned out pretty well




With the paper removed

Compared to the one from my 551


the 551 graticule stacked on top of the freshly cut 519.  Just different enough to be annoying.IMG_4367.JPG

Here it is, installed

Not bad for my first attempt.  I’m going to build a solid black aperture plate next.