Month: May 2019

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My New Old Analog Oscilloscope

An oscilloscope is the central piece of equipment in any electronics workbench. You use it to see and measure how electrical voltage varies over time.

The oscilloscope, or “scope”, produces a two-dimensional graphical display of a waveform. It displays voltage along the vertical axis and time along the horizontal axis. Scopes can display one or more waveforms on the screen, one for each input channel.

The older oscilloscopes are typically analog, non-computerized, scopes and display signals and waveforms in real-time. What you see is what you just measured.

Modern digital oscilloscopes have huge memory capacities. They display, measure, and record waveforms that can be played back and analyzed in great detail.

My New Old Scope

Scopes are expensive, but you can get a great deal if you settle for an older analog oscilloscope. I found this great little old analog scope on EBay for $50.

CS-5400 Oscilloscope
Kenwood CS-5400 Oscilloscope

My new old scope is the Kenwood CS-5400, a 3-channel, 100 MHz bandwidth analog oscilloscope. This scope is from the 1980s and made in Japan. It’s called a “Readout Oscilloscope” because you can read the measurements directly on the screen. Traditionally, the user had to visually look at the waveform on the grid and make measurements visually by eye. A screen readout was quite a fancy feature to have in its time. Considering that this scope is purely analog a direct screen read out is quite impressive. It is completely non-digital without a CPU or microcontroller under the hood.

Until now, I didn’t know that Kenwood, a Japanese company, made electronic test equipment or oscilloscopes. I was only familiar with Kenwood’s other products of ham radio and stereo audio systems. The big names in oscilloscopes are typically Tektronix, Hewlett-Packard was Agilent now Keysight, Rhode-Schwarz, and more lately Rigol and Siglent. But Kenwood is unknown for test equipment in North America. But apparently, Kenwood (now Texio-Kenwood) is quite prominent in Asia, particularly in Japan.

It Works!

The Kenwood arrived from the seller nicely and safely packed and in good condition. Its only defect is that it’s missing a rubber foot on the front corner. It came alive when I turned it on. I plugged in a set of cheap oscilloscope probes and a power cord and I was in the oscilloscope business.

The first thing I did was to connect the probes to the calibration output. This output emits a fixed 1 KHz square wave so you can test your basic measurements and calibrate your scope probes (called Probe Compensation.) The screen readout said exactly 999.99 Hz at 1.01 volt peak-to-peak. Close enough, I was very happy.

Unfortunately, the scope did not come with an operating or service manual. In fact, I could not find any manuals for this scope on the internet either. So, if this scope breaks I would have to fix it blind.

Let the waveform measurements begin.

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You can never have too many power supplies

Every electronic project requires electrical power. Generally, electrical circuits need a supply of direct current (DC) electricity to operate. The energy source can be as simple as a battery, but we normally need a source of energy that lasts longer and can deliver much more energy at a much greater rate than a simple battery. Because the electricity coming out of the power outlets is alternating current (AC) our electronics circuits cannot make use of the electricity directly out of our power outlets. Thus, the need for a Power Supply.

What does a power supply do?

A power supply is a device that converts AC to DC electrical power1. But a power supply does much more than just convert AC to DC. A power supply provides an output voltage at a specific value, it delivers voltage or current at a constant, regulated, level, and can provide multiple adjustable voltages. Finally, the power supply has to be capable of delivering energy at a rate that is greater than the rate of energy consumed by the circuit that it is supplying.

So, I picked up this power supply on EBay.

LPD-421A-FM
Lambda LPD-421A-FM

Heavy and Rugged

These Lambda power supplies are heavy, rugged, and built like an armored tank. It is pre-owned and it’s a bit dirty, but it works. Not bad for $50 USD. There is a sticker on the back that says that the previous owner is a large company that makes copiers. This model is a dual output version and can supply power at two different voltages. Some circuits and devices need more than one voltage to operate, such as Operational Amplifiers. So having a power supply with at least one output voltage is a necessary requirement.

Each output can supply a voltage from zero to 20 Volts at a maximum of 1.7 Amperes. This translates to a maximum of 34 Watts (20V * 1.7A)2 per output. The two outputs can be connected together to get 40 Volts at 1.7 Amps for a total of 68 Watts. This Lambda is not powerful enough to power up vacuum tube circuits3. But 20 Volts is good enough for solid state projects. I will need more power supplies to do vacuum tube projects, and it would be nice to have power supplies that are programmable or computer controlled. You can never have too many power supplies.

Each output has a voltage meter and separate current meter. You set the output voltage with the Output Voltage knob. You can set the maximum output current that the power supply will deliver with the Current Limiter knob. A Current Limiter is a valuable feature and it prevents excessive current from damaging circuits.

The Specifics

Here are a few of the specifications from the Lambda product data sheet.

Lambda LPD Series
Lambda LPD Series Power Supply Specifications

The models in the Lambda LPD series are pretty much the same, varying only by the maximum output voltage. The specification for the LPD series states 0.01% regulation with 500 microvolts of ripple, that’s nice and constant and good enough for my projects.

I was fortunate to be able to find the instruction manual for the Lambda on the internet, because this model dates to the late 1980s. The manual is quite complete, it includes schematic diagrams and a chapter on the Theory of Operation of the power supply. An amusing option is the “fungus proofing”, a MIL-V-173 military standard anti-fungal treatment, that was available for an extra charge. I guess this military quality equipment is designed to be used anywhere in the world and under all kinds of environmental conditions.

Finally, the data sheet says that this Lambda LPD-421A-FM had a list price of $613 USD in 1980s dollars. That’s an expensive power supply even in today’s dollars, but not bad at all for $50 USD.

  1. A circuit called a rectifier converts AC to DC and a circuit called an inverter converts DC to AC. [↩]
  2. Watts = Volts * Amperes [↩]
  3. Vacuum tube circuits require hundreds of volts [↩]
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My First Piece of Equipment

Finally, the first piece of equipment for the lab has arrived, a new Fluke 101 handheld digital multimeter1. It’s a very modest start, but it is just the beginning.

Basic Measurements

Fluke101
Fluke 101 Multimeter

Anybody who works with electricity needs a device that measures the absolute basics, a multimeter2. I wanted something simple and inexpensive but built with quality. And for fundamental electrical measurements, Fluke is one of the brands that first comes to my mind, the other being Keithley Instruments.

There are many reviews on handheld multimeters, on the EEVBlog3 and on YouTube, created by many handheld multimeter enthusiasts. I didn’t know there were so many different brands available (and I didn’t know that there were so many multimeter fanatics).

Specifications

The Fluke 101 is a simple device and it fits nicely in the palm of the hand. It measures AC and DC Voltage (up to 600 Volts CAT III)4 , AC Frequency, Resistance, and Capacitance. It also tests for electrical continuity and tests for defective Diodes as well. And it comes with a set of Fluke quality test probes with batteries included. Other competing products have more features, but for my first device, simple is better. But the Fluke 101 does not measure electrical current. So, I will have to pick up other pieces of equipment to fill that measurement deficiency.

A Tough Little Meter

There is a YouTube video where the reviewer pumped a full 13,000 Volts into the Fluke 101. This little meter absorbed all that voltage with no problems at all..

This is one tough little meter.

  1. A digital meter displays the reading in numerical digits while the more traditional analog meters display the reading with a moving needle along a printed scale [↩]
  2. A meter is an instrument that measures some quantity, e.g. voltage. A multimeter is an instrument that measures multiple quantities, e.g. voltage, current, and resistance. [↩]
  3. See the multimeter review spreadsheets. [↩]
  4. CAT III is a safety standard that enables the instrument to be resilient to high energy transients. [↩]