Thursday, June 13, 2019

Eldorado 325A Frequency Counter

My latest acquisition from eBay:

From the seller's photo (heavily retouched by me)
Works perfectly down to 1Hz. I haven't tested the high end yet. I had a shoot all set up but as usual a disaster cropped elsewhere. I'll update this post with more pictures later if I have the chance.

$67. I was the only bidder.

The next day a model 224 with only four settings went for $65. 🙄

Friday, June 7, 2019

Systron Donner 6052 Frequency Counter

This is a work in progress...

Here is an HDR image:
Click to enlarge
More to come

Friday, May 31, 2019

Systron Donner 8350 Reader/Generator

Here's a lousy shot of my Nixie tube timecode generator/reader:

Click for a much better view!
I'm not sure what tubes are in it but the envelopes are only about 2" high. The thumbwheels set the starting time for generator mode so it can be used as a Nixie clock. The entire case is only one unit high.

Note the two missing keycaps between "Hold" and "Power". The plastic has become so brittle that the ears snapped like twigs with I pulled them off to replace the light bulbs. Not only does it look stupid but without the caps in place the switches can't be actuated.

I saved the pieces. I suppose they could be glued back together with a thin, springy piece of steel reinforcing the joint and making it flexible enough for them to be put back on again.

If I had new, blank caps I could reproduce the text with decals. If anyone has a fix please message me.

Perhaps later I'll have time to take a better picture and get some interior shots. And get the part numbers on the tubes.

Thursday, May 30, 2019

2015 iMac Teardown and Second SSD Installation

A few months ago my iMac 17,1 made some very scary noises. It sounded like a loose plug in an AC socket arcing away accompanied by some hissing. There was no magic smoke, no smell.

Last week we tore the machine all the way down to inspect it. The power supply had no visible damage or odor. The AC socket and wires were OK. The mystery remains a mystery.

While we had it open I installed a second SSD in the HDD bay. Because the machine shipped with an Apple SSD on the logic board and no hard drive in the HDD bay I didn't know if the mounting brackets were installed. I found conflicting reports online. What I knew for certain was that the SATA cable to the HDD bay was not installed so I purchased a new one.

I also purchased an SSD installation kit from OWC which included a 1TB SSD, 3.5" to 2.5" adapter, "pizza cutter" tool for detaching the display (which is glued on), a thermal sensor and the adhesive tapes for re-attaching the display.

I got lucky—the drive brackets were there along with a lot of dust:

Thank you Apple
The only thing I didn't have were the pin-shaped screws that go into the grommets on the HDD brackets. We managed to fasten the drive adapter in place with some regular drive screws. They fitted snugly in the grommets and it's very unlikely that any of them will vibrate loose.

New SSD in place
(Note that I installed a 500GB Samsung EVO 850 that I already had on hand. I'm saving the OWC 1TB SSD from the kit for an external enclosure.)

There was one heart-stopping moment when the display slipped out of our hands and the bottom landed about 1/16" above the lower edge of the housing. We very carefully pulled it loose without breaking the glass and put it back in place correctly.

I held my breath again as I pushed the power button. The machine chimed, the fan spun up, and the display came on. What a tremendous relief. I spent weeks researching every aspect of the project and in the end it paid off.

Next up—install Mojave on the second internal SSD and find out how much of the software I use on a regular basis in El Capitan is broken. I'm going to buy a 2019 iMac as soon as refurbs start turning up in the Apple Refurbished Products store. Then next generation iMac will require macOS 10.15 Catalina (or later) which will no longer support any 32 bit software so a 2019 could be my last Mac purchase for a long time. No new Mac Pro and 6K Retina display for me even if I could afford them.

So that's my story. I've used it for months since the scary incident with lots of heavy gaming sessions cranking the cores and the GPU up to the max without any problems. Fingers crossed.

Finally, I could never have done all this by myself! I can't thank my buddy Bogart enough for his help.

Saturday, July 28, 2018

Scintillation Probe Kit

Prologue: A New Geiger Counter...

With the arrival of a new Geiger counter with a x1000 scale it was finally time to assemble the scintillation probe kit I purchased from Iradinc in 2014. The probe only required 900V so the stage was set.

The first hassle was to clear off enough space on my decrepit workbench.

The Kit: Some Assembly Required...

The pieces of the puzzle (click to enlarge)
Left to right: 3" diameter 2.25" plastic crystal; Hamamatsu R6233 Photomultiplier tube; tube cap; BNC connector; voltage divider parts; silicone grease; huge diameter heat shrink tubing.

Additional materials (click to enlarge)
Isopropyl alcohol, spray adhesive, electrical tape — all as recommended by the GeigherCounters group brain-trust. I still haven't found any 99% isopropyl alcohol locally but I did get some 90%...

The first step was to wire up the resistor string on the base of the PMT. My eyesight has been going downhill for years and this was somewhat of a challenge. The markings on the tiny resistors were very hard to make out. I was very nervous about plunging in and naturally I managed to scratch the insulation off of one. Tom was kind enough to send me some spares so I dodged that bullet.

PMT voltage divider complete (click to enlarge)

BNC connector attached (click to enlarge)

At this point it was time to glue the cap to the PMT. Unfortunately, the silicone rubber I had bought turned out to be the type that gives off acetic acid while curing. This damages electronic components.

I had specifically searched for and bought what I thought was "neutral cure" but somehow managed to screw that up. Yet another delay as I waited for the correct adhesive to arrive (once again I couldn't find any locally).

Cap glued to PMT (click to enlarge)
The plastic crystal is highly fluorescent and glows beautifully under 365nm UV light.

Crystal fluorescing. In a dark room it's quite bright. (click to enlarge)

Perfect fit (click to enlarge)
I did not bother to polish the crystal. I was too nervous at this point to be able to without mucking things up even more. A voice of experience told me not to sweat it so...

Next up was attaching the crystal to the PMT. I carried the bag of silicone coupling compound to the workbench, went to get something else, sat down and... the silicone grease was nowhere to be found on my cluttered workbench. AUGHHH!

Fortunately I had some more in another PMT wiring kit but my nerves were wearing thin. I proceeded with taping the crystal to the PMT and quit for the night. The next day I wrapped the entire assembly with layers of electrical tape and glued the front scrim on.

I took everything into a windowless bathroom and sealed the door. I powered up the Geiger counter and was highly relieved to hear lots of background counts. The relief was well-earned.

Taped and working. (click to enlarge)

It took me a couple of weeks to reach a point where I was ready to finish things up with the very large piece of shrink tubing. My job was a bit sloppy but I was satisfied with the result when I heard background counts again. Mission accomplished.

Heat shrink shrunk. (click to enlarge)

By the way, if you happen to see a small plastic bag labelled "Silicone" anywhere please let me know.

A big thanks to Tom Hall for this kit and his support. A very special thanks to K0FF without whose help none of this would have been possible let alone gotten done. Bravo.


I found the missing silicone grease. It was on my workbench all along amidst the bubble lights. Look closely. Very closely.

Closer. Closer... (click to enlarge)
Right there the entire time. I told you my eyesight is deteriorating.

Tuesday, October 25, 2016

Craig Anderton's Multiple Identity Filter

Craig Anderton's Multiple Identity Filter™ originally appeared in a series of ariticles in Contemporary Keyboard in 1979. It is a CEM3320-based VCF with each of the four stages operating semi-independently. Each stage has...
  • Three Filter Modes: Lowpass, Highpass, Allpass
  • Two frequency ranges (10:1 ratio)
  • Series/Parallel Switching
Add to that voltage-controlled resonance, straight/filtered signal mixer w/phase inverter (for phasing, changing bandpass to notch, etc.) and more. Craig was in top form—this is one tricked-out VCF.

Here is the article: MIF.pdf

Here is a mirror on Mediafire in case the link above doesn't work for you. I've been told that some web browsers (or their extensions) warn that Mediafire is a dangerous site. It's not but the page does have a lot of extraneous links and other junk that can make it confusing to navigate. To start the actual download of the pdf file click on the big green "DOWNLOAD" button that also has the file size in smaller letters: MIF pdf

Update 2017.2.26

Note that this design is not optimal. More work has to be done to get the stages to "behave" properly. This has been discussed on the Synth DIY list on multiple occasions. There is a searchable archive here: SDIY Archive

And there's some very good news: a clone of the CEM3320 has been fabbed. It's available here and the price is very reasonable. The datasheet is here.

Wednesday, February 24, 2016

The Oscilloscope Artist

The Oscilloscope Artist originally appeared in the November, 1975 issue of Popular Electronics. It creates all sorts of fascinating moving geometric patterns on an oscilloscope screen.

All you need is a low bandwidth 'scope with horizontal and vertical (XY) inputs.

Update (2018/02/16): David Dixon spotted a really stupid typo in the original pdf file that was shared below. This has been fixed and the latest version is now 1.2.1. All other (unattributed) copies floating around the Internet are of the earlier, incorrect version.

A reconstruction of the complete article is in a pdf file. All the original parts are still available!

The original block diagram is a bit confusing so I redrew it. Oscillators A & D create a Lissajous figure baseline from triangle/square waves. Oscillators B & C are multiplied and summed with A & B.

To make things interesting, C is 90° out of phase between the multipliers. All the oscillators are sync'd to A, which is ~60Hz. All of this produces complex patterns which move and shift.

I've also used it with a laser projection system with X and Y galvos and it works although the corners aren't too sharp.