So I recently got a Keithley 196 digital system multimeter with 6 1/2 digits which was sold as “broken - parts only” for virtually nothing so I figured in the worst case I have something to salvage parts from.
After it arrived I tried to power it on - nothing. Line fuse was okay, so I started checking the power rails, on the analog board the +15V, -15V and +5V were fine. On the digital board however I found the problem: the digital +5V rail was missing, I traced this to the transformer not providing AC on the secondary winding used for the digital supply. Before I started to trace the problem further or bother to repair it, I soldered two wires onto the unregulated DC side of the bridge rectifier for the digital 5V rail and powered that from a laboratory supply - bingo it started right up.
Erlichsee 14.08.2022
All pictures taken with a GoPro 7.
Dual Channel Microscope Lamp Dimmer
I built another lamp controller for my microscopy lights. This is a simple DC dimming circuit designed for 15W tungsten microscopy lights, such as for my LOMO OI-19 (ЛОМО ОИ-19). Though I have a couple other similar lamps from Carl Zeiss Jena and Leitz.
The circuit is powered using an external 7.5V 5A power supply. I calculated the heat sink to heat up 40K in the worst case, assuming around 20C room temperature this is still within the limit of the polystyrol enclosure.
Microscopy Lamp for LOMO Microscopes
One of my LOMO microscopes came with a LOMO OI-35 (ЛОМО ОИ-35) illuminator, the other just with a mirror for an external light such as theLOMO OI-19 (ЛОМО ОИ-19). So I figured to machine myself a light fixture for a 3W LED light.
Lamp fixture I did not do any drawings for this and just figured everything out while machining it.
I then spray painted the lamp fixture white and added a LEE diffuser filter.
Audio Isolation Transformer
The Intimo 5430 tube radio I recently restored has a DIN-5 for an external playback or recording device. So I figured to build an adapter, such that I can hook the radio up to a computer audio output.
The schematic itself is fairly quite straight forward. The diodes are 1N4007 and are primarily designed to absorb any high voltage pulse that may couple through the transformer if something goes wrong in the radio.
Restoration: Intimo 5430 Tube Radio
I recently got this GDR/DDR made Intimo 5430 tube radio. A particular special feature of this radio is the EM84 tuning indicator tube.
Fixing the Wood case The case looked like as if someone had a flower pot or something standing on it, there was signs of water ingress. I decided to first sand off the wood with 160-180 sand paper and then apply two layers of wax finish to it. This turned out to work quite nicely.
Fixing a Soviet Space heater Луч
I recently got this old 1.2kW soviet made space heater of type “Луч”. The heating resistors/spirals are fine, but the fan was making loud noises. This usually indicates a bad bearing somewhere. Furthermore the heater had a unearthed East-German/Soviet type Schutzkontaktstecker compatible plug, which I was going to swap out to an earthed plug (and also a respective line cable with earth wire).
The inner workings are fairly simple: There is a thermal cutoff, then a rotary switch selects which of the heating spirals get supplied and also powers the synchronous motor. A really interesting thing is the thermal cutoff which is a Bimetallic strip but rather than using a mass produced thermal cutoff, they did one customly.
Microscopy Insights #7
Pictures taken with a Sony SLT-a37 on my MBS-10 (МБС-10) with the МФУ tube.
Porous Concrete Exploded X2 Class Capacitor This capacitor was from my HP 8112A pulse generator, it had a catastrophic failure. I removed it and replaced it with a new one, the pulse generator is working again, albeit it is still somewhat stinky.
Moth An unspecified type of moth, I’m not quite sure about the species. Anyone any idea?
Frequency Standard System: Clock Divider Mk1
This is part of my Frequency Standard System.
This board derives utility frequencies off the main 10MHz frequency signal. It has four 50Ω TTL outputs for: 5MHz, 1MHz, 1KHz and 1PPS. The 1PPS signal is driven by a 74HC123 monostable multivibrator from a 1 Hz signal that gets divided down using 74LS90 dividers.
Funkwerk Erfurt 8600a Stelltrafo
I recently got this east German Funkwerk Erfurt Stelltransformator 8600a, which is a 250VA step transformer with 14 steps and a ratio display.
Picture taken after the fixes outlined in this article
First thing I saw broken was the plug. The original one out of bakelite broke in an unrepairable manner. I replaced it with another bakelite plug I had sitting around. Cleaning the inside In order to cleanup the inside I completely disassembled and reassembled the unit. (Yes I fixed the cables on the right to look like they did before after taking this photo)