Scissors for electricians PROSKIT DK-2047N is a multi-function electrical cable cutting and stripping scissors for electrician. DK-2047N is originally designed for telephone and electrical maintenance.

DK-2047N Electrician’s Scissors has total length of 145mm and cut length of 47 mm.
It has comfortable and sturdy plastic handle. The price in different sources is around 10-13 Euros.

The DK-2047N scissors is designed to cut up to 16 AWG solid wire (1.3 mm2) and 12 AWG stranded wire (3.3 mm2). The scissor has double stripping notches to strip 18 and 22 AWG wire. There is also a scraper and file on side edge of blade.

I have found it at an useful tool in electronics work table as general purpose scissors. I can use this tool to cut wires, component leads, thin metal sheet (copper or aluminum), plastic material, paper, cardboard, plastic tapes etc.. It is the scissors I keep on my electronics workbench.

Soldering guns feature more power than soldering irons, typically between 75 watts up to 300 watts for industrial use. The pistol shape provides more control in cramped work areas. Soldering guns use transformers to convert power to a low-voltage current to heat up the loop-shaped tip. The temperature of the soldering tip is regulated manually by holding the button until the solder melts, and then releasing it. When the solder is about to start solidifying, the button is pressed again, and so on.

Pistol-grip electrically-heated soldering tools had been used since the 1920s. In 1941 Carl E. Weller invented and later obtained U.S. patent 2,405,866 for a transformer-based soldering tool which heated and cooled rapidly.

In a Facebook posting at https://www.facebook.com/share/r/GtYhqGWTkDC1ezae/ there was an interesting video reel mentioned with comments:

https://www.facebook.com/reel/3218593264944072

This is interesting….. Anyone know what is the typical AC amperes flowing in a soldering gun secondary, solder tip? Say, 120 watts?
Or, has anyone measured the AC voltage across the heavy screw terminal output clamps of the gun, at the resistive loop terminals?
Then, in this app, is the modified solid copper wire coil coupling AC secondary power to the metal crucible, inductively? Or simply ohmic-ly Through the coil’s contact with the solder cup, and driven by the
low voltage, high current solder gun secondary?
Nice quick solution for a solder cup.

Here are some of my comments to it:

This is interesting….. Anyone know what is the typical AC amperes flowing in a soldering gun secondary, solder tip? Say, 120 watts?

I have one 100W Biltema brand soldering gun. The current flowing in original it is around 80-90 amperes.

Or, has anyone measured the AC voltage across the heavy screw terminal output clamps of the gun, at the resistive loop terminals?

I measured voltage of around 350 mV AC when the original soldering tip is in place. The open circuit voltage without tip was around 560 mV AC.

Based on those numbers the actual heating power on the tip is closer to 30W than advertised 100W. The iron seems to take around 95W power from 230V mains outlet.

Then, in this app, is the modified solid copper wire coil coupling AC secondary power to the metal crucible, inductively?

This few turns coil does not give much inductive heating effect at 50 Hz.

Or simply ohmic-ly Through the coil’s contact with the solder cup, and driven by the
low voltage, high current solder gun secondary?

That would be the main heat source.

Anyway an interesting soldering cup hack idea. It might not be suitable for a long working time. This soldering iron says operating cycle to be 12 seconds maximum drift time followed by 48 seconds pause.

More soldering guns ideas:

Free Replacement Tip for Soldering Guns
https://www.instructables.com/Free-Replacement-Tip-for-Soldering-Guns/

Homeade Weller soldering gun tips DIY
https://www.youtube.com/watch?v=U86GsflNjJQ

Home Made Weller Tips Cheaper and Better than Original
https://www.youtube.com/watch?v=DS4plN51Deg

Tech Tips Tuesday, Super Hot Soldering Gun
https://www.youtube.com/watch?v=79uD6XwBg5E

5 Amazing Soldering Iron Gun Tips – Life Hacks
https://www.youtube.com/watch?v=vU9Avha4oRk

Dual impedance digital multimeters have feature to control the input impedance of the multimeter. LoZ stands for Low Impedance (Z). This feature presents a low impedance input to the circuit under test. A typical digital multimeter has typically around 10 megaohms input impedance, which loads the circuit being measured very little, but can pick up noise easily in some applications. For example when working with electrical power AC circuits, the multimeter can easily pick up noise from nearby wiring. LoZ feature in some multimeters is designed to reduce the possibility of false readings due to ghost voltages and improves accuracy when testing to determine absence or presence of voltage.

The “ghost voltage” reading you get from in multimeter screen is a real voltage and although high in amplitude it is potentially very weak due to it being sourced via a high impedance. A high input impedance measurement device (o-scope, multimeter etc.) can measure this voltage with little or no obvious reduction in the amplitude of the voltage but, a low impedance device will try and take current through the inherent high impedance in series with the voltage, and the voltage will collapse in amplitude, sometimes just to a few milli volt.

Ghost voltage is just a voltage that is in-series with a very high impedance. For instance you can capacitively couple to AC voltages in house wiring and this coupling might only be 50 pF. An oscilloscope will display the voltage on your body and tell you that the voltage is a few volts peak to peak yet, 50 pF has an impedance at 50 Hz of 63.7 Mohm. This will form a potential divider with your o-scope input (usually 10 megaohms) and the 120 VAC might drop to around 10 or 20 volts. Prior to connecting the multimeter the voltage would be higher. These voltages are real, not “ghosts”. Very many digital multimeters have also around 10 megaohms impedance on voltage measurements range.

Ghost voltages are voltages that exist where they shouldn’t. Many technicians use the term “ghost voltages” to refer to compromised voltage sources. However, technically, ghost voltages are those that are inductively or capacitively induced by the proximity to other wiring. One example is when two wires run in parallel, which effectively acts like a capacitor. A capacitor consists of two metal plates separated by a distance and can store an electrical charge. When the voltage changes, or it is an AC voltage, it reduces the overall impedance (actually reactance, but let’s simplify) between the two plates, which can cause a voltage to appear in the nearby wire.

AC current is flowing, but it is small. If you substitute voltmeters having lower internal resistance, you’ll measure lower AC voltages. The LoZ feature on your multimeter takes advantage of a “voltage divider” concept. The conclusion here for each resistance in a series circuit is: “The higher the resistance, the higher the voltage. The lower the resistance, the lower the voltage“. Those high voltages that show at with high impedance measurement mode but disappear on LoZ mode are “ghosts”

Traditionally most electricians and plant maintenance professionals have used some form of solenoid tester to determine whether circuits were energized or not. Because of their low impedance circuit, solenoid testers are not fooled by ghost voltage. Adding LoZ to multimeter potentially avoids the need to carry an extra tool with you in addition to a multimeter.

LoZ is very useful for electrician type applications. But it is not suitable for tracing a electronics circuit with intentionally high resistances. Sensitive electronic devices or components on control boards may not tolerate the additional load introduced by the LoZ function. If you use LoZ in such cases, it can disrupt the intended behavior of the circuit and provide inaccurate readings or even damage components.

Overall, understanding the advantages and limitations of the LoZ function can greatly assist in diagnosing electrical issues and ensuring accurate voltage measurements.

What is the input impedance of an instrument? What are ghost voltages and how to detect them?
https://www.youtube.com/watch?v=htx6oLx1gBs

How To Determine If Voltage Is Real Or a Ghost Voltage Using your Fluke Digital Multimeter
https://www.youtube.com/watch?v=mRwsxmn2P-s

How to Turn Off Ghost Voltages with Dual Impedance (LoZ) Meters
https://www.youtube.com/watch?v=JRXTFxsA_lA

Some technical details of LoZ on some multimeters:

Low Impedance Voltage Measurement (Lowz) – Kaiweets HT206B User Manual
https://www.manualslib.com/manual/2074243/Kaiweets-Ht206b.html?page=11 says:

Low impedance voltage measurement (LowZ)
LowZ mode allows you to measure AC voltages with a low impedance (approx. 300 kΩ).
In this mode, the multimeter lowers the internal resistance to prevent ‘phantom’ voltage readings.
As a result, the circuit is more heavily loaded than in the standard measuring mode.
Set the rotary switch to “LowZ” to use the function.
The LowZ voltage measurement must not exceed 600 V.
Due to the reduced impedance, this measurement function is not suitable for continuous
measurement. A max. The measurement duration of 1 minute must be observed

Fluke document at says https://www.fluke.com/en-us/learn/blog/digital-multimeters/dual-impedance-digital-multimeters

With dual impedance meters, technicians can safely trouble shoot sensitive electronic or control circuits as well as circuits that may contain ghost voltages, and can more reliably determine whether voltage is present on a circuit.

On the Fluke 114, 116 and 117 DMMs, the meter’s regular Vac and Vdc switch positions are high impedance. Use these switch positions for most troubleshooting scenarios and especially on sensitive electronic loads.

The Fluke low impedance function is called Auto-V/LoZ. Auto-V stands for automatic or volts. This feature automatically, determines whether the measured signal is ac voltage or dc voltage, selects the correct function and range, and displays the correct information. LoZ stands for Low Impedance (Z). This feature presents a low impedance input to the circuit under test. This reduces the possibility of false readings due to ghost voltages and improves accuracy when testing to determine absence or presence of voltage. Use the Auto-V/LoZ switch position on the DMM when readings are suspect (ghost voltages may be present) or when testing for the presence of voltage.

Most digital multimeters available today have an input impedance that’s high enough to show the capacitively coupled voltage, giving a false impression of a live conductor. The meter is actually measuring voltage coupled into the disconnected conductor. However, these voltages, at times, can be 80-85% of what the “hard” voltage should be. If not recognized as a ghost voltage, additional time, effort and money will be lost troubleshooting circuit problems.

The most common places to encounter ghost voltages are blown fuses in distribution panels, unused cable runs or electrical wiring in existing conduit

With a dual impedance meter, select the Auto-V/LoZ function. This function has a low input impedance on the order of three kilohms. When the leads are placed on an open circuit that contains a ghost voltage, the low input impedance will cause the ghost voltage to dissipate and the meter will display a reading near zero volts indicating no voltage present.

When the multimeter has an input impedance of few kilo-ohms, the downside is that if put in high voltage, a lot of power is lost inside multimeter. It seems that some LoZ multimeters use an adaptive input impedance, that is few kilo-ohms at signals that have amplitude of several volts (meaning up to few mA current), and increases the impedance when the input voltage gets higher (to something like 100 kOhms at full mains voltage, meaning around 1-2 mA current through multimeter).

UNI-T says at https://meters.uni-trend.com/faqs/acv-loz-low-impedance/ on LoZ:

ACV LOZ Low impedance

Low impedance input: False voltage generated by large capacitive equipment can be measured.
The input impedance of a low-impedance multimeter is 300kΩ. It can discharge the residual voltage and determine whether the residual voltage exists.
The input impedance of an ordinary multimeter is as high as 10MΩ. Therefore, residual voltage cannot be identified, resulting in misjudgment or security risks.
There will be residual voltage after powering off large capacitive equipment.
Applied to all electrical equipment, such as reactive power compensation cabinets, large commercial fluorescent lamps.

Low impedance voltage testing (LoZ) discussion at https://electronics.stackexchange.com/questions/463151/low-impedance-voltage-testing-loz has following information bits on how LoZ mode is implemented on some multimeters:

On BM829s, Lo-Z gives you 500kOhm at 1000V, 320kOhm at 600V, 125kOhm at 300V, 18kOhm at 100V: an extremely convenient autoranging capacitor discharge device!

Here is a video overview of the meter:
Banggood – Small Pen Style English Speaking Multimeter: MUSTOOL MT007 Pro-EN
https://www.youtube.com/watch?v=lt4seQmWFVY

MUSTOOL MT007 Pro-EN Specifications:

DC voltage: 0.8-1000V
AC voltage: 0.8-700V
Resistance: 0.1-60MΩ
Capacitance: 10nF- 60mF
Frequency: 1Hz-10MHz
Temperature: -20°C-50°C/0-122°F
Diode: 3.0V
Buzzer: 0.1-50Ω
Fire distinguish: yes
Phase sequences：yes
Flashlight: yes
True RMS: yes
Power supply: 1.5V AAA*1
Low voltage prompt: yes
Automatic shutdown: yes
Backlight: yes
Keeping data: yes
Size: 171*21*21mm
Net weight: 80g

MUSTOOL MT007/MT007 Pro Digital Multimeter丨Pen Multimeter – Banggood Tool Sets

Ranges (spec):

* V=/V~: 6V, 60V, 600V (0.5%+4)
* V=: 1000V (0.8%+10)
* V~: 700V (0.8%+10)
* R: 600Ohm (0.8+5), 6k, 60k, 600k, 6M (0.8%+3), 60M (2.5%+3)
* C: 10nF, 100nF, 1µF, 10µF, 100µF, 1mF, 10mF (3.5%+20), 60mF (5%+3)
* T: -20°C … 50°C (1°C res, 1.0%+5); °F available as well
* NCV
* Neutral/Live test
* Non contact phase sequence measurement

It’s very small, like a marker pen. The meter came packed in standard Banggood shipping bag. Inside this the meter has it’s own cardboard box. In the box is the meter a test lead and instructions booklet (Chinese and English).

Very practical, compact, light and complete for most measurements. It has automatic operation mode that does most normal measurements nicely, and you can manually select the measurement range if you need. The display is bright and sufficiently readable despite its small size. The display is clear and the display is updated quite fast! The power supply is one 1.5V AAA battery.

Product corresponds to the description. Quality and workmanship are very good. Measurement results are precise and easy to read. Testing it briefly showed that it works well. The product turned out better than I expected. I like the screen resolution, the color offers a very good and clear image. The display is clear and the display is updated quite fast for most measurement!

I find this multimeter very useful to make measurements while keeping a vision on the display which is very bright and sufficiently readable despite its small size. The values recorded during the measurements were very accurate. Voice feature let’s me to get the reading even when I am not looking at the display.

Evaluating a multimeter

Form factor: It is like fat marker pen. Easy to carry and easy to use. It is very good size to have it always in your trouser pocket. Easy to measure, it has auto mode for everything so you only put the leads on your testing point. Good buzzer works immediately when you touch measuring leads without needs to push any button. It has also led indicator and flashlight to point the measuring tip.

Functionality: Check the range of measurement capabilities are voltage, resistance, capacitance, temperature, non contact voltage, live/neutral wire detection and three phase sequence test. An advanced and practical multimeter with multiple functions at a low price. This meter has also built-in small LED flashlight. It is good because it is small in size, has automatic operation, and has everything you need, as well as those large instruments. Nice and comfortable tester. 6000 resolution counts, 3 and 5/6 bits. Not a laboratory device, but for domestic and semiprofessional applications the most necessary. Nice and handy tester.

Display and User Interface: This meter has a small but clear and easy-to-read display. The meter different operations are performed with three buttons. The product is very easy to use in AUTO mode. After some learning you get to know how to turn on other modes. All his functions are functioning properly and stable. Display works well from different viewing angels. It works fine in dark environments (display light always on), but becomes very hard to impossible to read with direct sunlight on it.

Automatic Power Off: To save battery life, the meter automatically switches off after five minutes of inactivity. This feature cannot be turned off.

Special features: The MT007 PRO-EN meter can speak out the measurement results in English. The broadcast voice language only supports English. MT007 PRO-EN is with voice on by default. The voice that is by default turned on is sometimes slightly annoying but will be handy when using the meter in tight spaces where you can’t see the display. If you want to use the meter without voice, you can do that when you you press and hold the N/LP button and turn on the multi-meter, the voice broadcast will be cancelled.

Accuracy and Precision: A good multimeter should provide accurate and precise measurements across various ranges. This meter offers 6000 resolution counts, which means 3 and 5/6 numbers. The readings were pretty accurate. This meter is not a laboratory device, but for domestic and semiprofessional applications works OK.

True RMS too! The measurements I tested were within the advertised tolerance. Actually the accuracy of the tested meter is much better than the specifications promise in voltage measurement. This device can measure the true RMS value of an AC voltage accurately. The manufacturer promises AC measurements to work from 50 Hz to 800 Hz accurately (0.5% or 0.8%). If you are satisfied with an error of approximately 5 %, you can measure AC voltages between 10 Hz and 2 kHz.

Build Quality and Durability: The quality of the materials used and the overall build of the multimeter seems to be OK. The product turned out better than I expected. Beautiful, useful and very practical. Comfortable in hand. I find the cable probe a bit stiff for this size device but otherwise it is a very good device.

Safety Features: Generally for multimeter safety we should look for features like overload protection, fused inputs, and proper category ratings to ensure safe usage in different environments. This meter feels OK. Supplied measurement cable looks safe and meter itself looks OK. Probe tip covers included and removeable, which is a plus. The multimeter manufacturer mentiones IEC1010 standard, but does not specify any CAT safety class for this. So we should expect that this meter belongs to lowest CAT I category, which means it would be suitable only for Electronic Devices testing anything from a small circuit board to larger device with high-voltage but low-energy. It might not be safe for single phase AC loads measurement. This is not a disaster for measuring in PCBs that are powered by low DC voltages. In principle, you should not use this device with its EF, LIvE and PA functions, because there is a direct link to the mains voltage. While the device behaved correctly at 230V AC, I would highly recommend not to use it regularly at more than 50V~/120V= or better stay below the 30/60 boundary to be sure. This multimeter does not have fuses in it, and can go without them because it does not have any current measurement range.

Missing features: The features this meter misses compared to many other multimeters is that MT007PRO-EN cannot measure current and frequency. It does not come with a carrying pouch but the box is sturdy enough for carrying.

Price and Value for Money: The price of the multimeter in relation to its features and overall quality seems to be OK. The lack is safety CAT rating a minus. If you plan to use this only for low voltage electronics measurement, this would offer good value of money.

Different measurement modes operation

The red one is the most important. After pressing this button for two seconds, the device is switched on. The display shows ‘Auto’ as an indication that the fully automatic measuring function is switched on. In this mode, the meter should decide by itself which measuring mode you want to choose. This works perfectly if you connect a DC or AC voltage or a resistor to the meter. .

With the second button ‘HOLD’ you can freeze the measured value on the display.

With the third button, you switch to the AC voltage detector function. This gives you three options, which can be called up again by briefly pressing the button several times: EF (Indication of electric fields), LIvE (Live or neutral wire indication) and PA (phase sequence indication in a tree phase connections). If this button is pressed for more than two seconds, the LED flashlight above the measuring pin turns on or off.

AUTO mode: In auto mode, the voltage readings are fast and continuity is delayed by about a second. Resistance readings are delayed by the same amount of time. Input resistance in auto-mode is around 10 megaohms.

Manual Voltage mode: In manual mode, voltage readings never take longer than about half a second. The specifications say it does three measurements per second.

Measuring resistances: The specs give an accuracy of ±(0.8 % + 5 digits), my meters performs much better. The resistance checking is only under “AUTO” mode. The measurement time is a bit slow. It can take few seconds for the resistance reading to settle.

Measuring capacitors: Also when measuring capacitors, you usually have to set the measuring function by hand. This is done by pressing the red button briefly several times. It works OK and seems to give accurate results, but it is bit slow. Capacitance test takes about 3-4s and takes a couple of readings to settle down at higher values. Measuring especially large capacitors such as electrolytic capacitors is very slow taking many seconds up to over 10 seconds. As was to be expected, large errors occur when measuring electrolytic capacitors like with many other multimeters also. The reason is that this meter (like many other) uses a constant current is passed through the capacitor and time for capacitor to charge is measured. This method does not take into account the leakage current of an electrolytic capacitor. Some electrolytic capacitors that have a large leakage current and the capacity of such an electrolytic capacitor is measured with an error that can reach tens of percents.

Measuring temperatures: Temperature measurement is a quite useless function on this device. The temperature sensor is somewhere in the device on the PCB and the only thing you can measure is the room temperature when the meter had been in the room for a long time. Unexpectedly, pleasantly and undocumented, this meter can measure the temperature also with a K-type thermocouple when connected to the terminals and meter set to temperature measurement mode.

Continuity test: With continuity test mode built into AUTO mode, you can test low-impedance connections hearing beep when there is a low resistance between test leads. Good that the buzzer works immediately when you touch measuring leads in default AUTO mode without needs to push any button to activate it. The continuity testing mode is not very fast, it can take a fraction of second until the beeper reacts when you make connection. The open terminal voltage in AUTO mode when measured with other multimeter was around 0.6V the short-circuit current was around 0.16 mA. The threshold between beeping and not beeping is about 50 ohms.

The EF function: With the EF function, you should bring the measuring tip of the meter near a point on which the mains voltage is present. The red LED should then light up, the buzzer should beep, and the display should show a number of dashes indicating the strength of the 50-60 Hz field. This function is very sensitive, maybe too sensitive to be practical. Detect live voltage / voltage tester can’t be trusted.

The LIvE function: The LIvE function allows you to distinguish between live and neutral. If you touch a live wire, ‘OL’ appears on the display and the red LED and the buzzer are activated. Otherwise, the green LED lights up. This might not be a very useful functionality, because the meter lacks the necessary safety ratings for measuring mains wiring. Detect live voltage / voltage tester can’t be trusted.

The PA function: The PA function is only useful if you have a 3-phase connection where you want to know the phase order. There is a phase shift of 120° between the three voltages on the three live wires of a three phase connection. With this function you can look up the correct order of those three phases. Put the meter in PA mode and touch one of the phase connections with the tip of meter. The meter beeps briefly, the display shows ‘PA’. Then touch one of the other two phase connections with the measuring tip. If you now have the one that has been shifted 120° in phase from the first, the display will show ‘PAB’ and the meter will beep. Finally, touch the third phase, the meter beeps again and the display shows ‘PABC’. This might not be a very useful functionality, because the meter lacks the necessary safety ratings for measuring the voltages present on three phase connections. This meter is not safe to use it in an area where there is a phase sequence to be measured.

With all those functions this multimeter could be handy gadget for a service technician. However, due to the lack of a proper CAT rating, it is only allowed to be used in low-voltage circuit boards and not mains environment according to the European electrical safety regulations. This device probably would work in 230 V environments, but if something ever goes wrong, an insurance company can cause trouble about working with a CAT I device in a mains environment.

Here are some review videos of different MT007 multimeter versions (ones with and without voice broadcast).

Banggood – Small Pen Style English Speaking Multimeter: MUSTOOL MT007 Pro-EN
https://www.youtube.com/watch?v=lt4seQmWFVY

MUSTOOL MT007/MT007 Pro Digital Multimeter丨Pen Multimeter – Banggood Tool Sets
https://www.youtube.com/watch?v=Vfxax3DK1bE

MUSTOOL MT007 Pro EN True RMS Digital Multimeter + Voltage Test Pen + Phase Sequences
https://www.youtube.com/watch?v=LeWgePl4o9g

Mustool MT007 Pro – Review (Portugal)
https://www.youtube.com/watch?v=K5FA11Ffm6E

Banggood – Small Pen Style English Speaking Multimeter: MUSTOOL MT007 Pro-EN
https://www.youtube.com/watch?v=lt4seQmWFVY

mini pen multimeter full review|Mustool mt007 pro|mt007 pro|aneng a3008|kkm99|kkm100|rm206|a3008
https://www.youtube.com/watch?v=D2ks_I6A0aQ

Mustool MT007 Pro – Review
https://www.youtube.com/watch?v=K5FA11Ffm6E

Related reviews:

ANENG A3008 is a very similar meter (without voice broadcast) and you can find a review of it at
https://chinese-electronics-products-tested.blogspot.com/p/aneng-a3008-pen-multimeter-tested.html
Thar review tells how the product can be opened and shows what is inside: The two parts of the housing can be separated by unscrewing three screws and removing four self-adhesive stickers.

Another collection of teardown pictures can be found at
https://www.eevblog.com/forum/testgear/aneng-a3008-(6000-count-ultra-compact-pen-type-dmm)-review-photos-and-teardown/

How to buy:

From Banggood go to MUSTOOL MT007 Pro 3 in 1 Pen-type Digital Multimeter True RMS Multimeter + Voltage test pen + Phase Sequences Meter Color Screen page ans select with meter type (MT007Pro-EN model with voice broadcast).

My trusty MS8209 multimeter failed. It was the second same type multimeter that failed for me. Annoying, but not that bad that both of those multimeters had both lasted around 10 years or more for me.

I needed to get a new multimeter. I wanted a multimeter with the same environmental measurement ranges as my MS8209 had, because I need those occasionally. There is not very many multimeters with all those features on the market. The options I considered were:

• A new MS8209 but was out of stock many places with reasonable prices
• Mastech MS8229 that was marketed as improved follow-up to MS8209
• Biltema 6-in-1 meter 17-338

Considering availability, pricing and brand I decided to get the Biltema. The reasons was that it was cheapest, had decent specifications and I could pick it up quickly from their nearby shop. I have been happy with meters I have bought Biltema many years ago (very good considering the price meter made by Mastech). This Biltema 6-in-1 meter 17-338 had also won a multimeter test in 2019 in Praktiskt båtägande, #3/2019 magazine.

FEATURES
* Display: 4000 count LCD display with back light
* 6-in-1 multi-function multi-meter, Light meter, Sound Level meter, Relative Humidity meter, Temperature meter and NCV indicator.
* Auto ranging
* Data hold and relative function
* Auto power off.
* Double molded housing
* Safety design meets CAT III 300V and CAT II 600V
* Accessories: Instruction manual, 9V battery, test leads and K-type temperature probe

Technical specifications

Technical specifications:

Overvoltage category: CAT III 300 V
Operating temperature: 0–40 °C (less than 70% RF)
Storage temperature: -10–60 °C (less than 80% RF)
Temperature sensor: Thermocouple, type K
Display: 4000 count LCD display with back light
Measurement speed: 3 Hz (nominal)
Size: 170mm x 79mm x 50mm (6.7″ x 3.1″ x 2.0″)
Weight: 342 g ( 0.75 lb )

Measuring ranges:
Temperature -20–1300 °C
Humidity 33–99 % (measurement range)
Illuminance 0–40000 Lux
Noise level 35–100 dB (C)

Dimensions: 170 mm (height), 78 mm (width), 48 mm (weight)
Weight: 335 g
Battery: 6LR61, 9 V

Electrical data

Continuity: less than 50 Ω makes beep sound
Diode test: 1,4 mA (2.8V DC Open Circuit)
Current strength: 0–400 μA to 0–10 A (max. AC/DC)
Voltage range: 0–400 mV to 0–600 V (max. AC/DC)
Resistance: 0–400 Ω to 0–40 MΩ
Capacitance: 0–50 nF to 0–100 µF
Frequency: 0–5 Hz to 0–10 MHz
Duty cycle: 0,1–99,9 %

Meter review

Biltema 17-338 is is Multifunctional 6-in-1 multimeter with large backlit display for measuring voltage, current, frequency, duty cycle, capacitance, resistance, and temperature, and with diode and connectivity testing. In addition to electrical measurement functions, the multimeter also measures C-weighted sound level dB(C), illuminance (lux) and relative humidity. The multimeter has selectable functions for automatic range detection, current value hold function, saved value (relative value) comparison, non-contact voltage detector with LED indicator, as well as battery status indicator. The meter come with following accessories: fabric bag, temperature probe, set of test cables and 9V battery.

The display is quite normal looking multimeter LCD screen with backlight. Compared to many other multimeters, this meter has three numeric value displays instead of one one. There is the big main number display for the selected measurement in the bottom. On top of the big display there are smaller humidity and temperature displays. During the self test when meter is turned on everything is turned, all numbers and symbols. The display has a couple of indicators that is not used on this model of the meter.

In the center of meter there is rotating range selector that allows you to select the measurement type you want do, meaning if you want to measure voltage, current, frequency, resistance, capacitance, temperature, sound level or light level.

The Hold button will freeze the reading when pressed, usually this is very useful, but sometimes it can be very useful. Pressing Hold button for a longer time turns on the display backlight.

The Range switch button is used to manually select a range. First press will select manual range, the next presses will step through the ranges. Hold the switch down to change back to auto range. Most of the time automatic range selection is best, but having option for manual selection is a good to have.

Pressing Rel button stores the current reading and show all further readings relative to the stored value. Relative reading is sometimes very useful feature.

Ohm range measures resistance. Blue button is used together with the rotary switch to access some measurements functions. This is needed most often to switch between ohms and releated function, i.e. continuity and diodes. The continuity beeps at around 50 ohms or lower resistance.

CAP range is used to measure capacitance. The measurement results seemed to be according what was promised on the manual for several capacitors I tested with it. The measurement ranger can measure up to 100 uF. Smallest resolution is 10 pF.

Hz% range mode can measure signal frequency or duty cycle of PWM signal. Use HZ % button to select between modes. Frequency measurement can measure from 1 Hz to 10 MHz. The PWM measurement works at frequencies from 5 Hz to 15 kHz.

Temperature for temperature there is built in and external type K, can be switched between C and F degrees. The built in thermometer and humidity sensor show the results all the time on the screen. The meter comes with a small type K temperature sensor that can be used for temperature measurement. Any external type K temperature sensor can be connected to the multimeter with a supplied adapter.

Audio volume dBC range measures 35-100 dB at frequency 30 Hz – 10 kHz (C weighting). This is not very accurate, +-5 dB error possible. In my measurement the measured decibel values were quite near to those given by my PARKSIDE sound level meter and app on my smartphone.

Light level 1-400 Lux and 10-40000 lux range. It seems to be giving quite believable results. The measurement results matched quite well to the readings my lux meter smartphone app gives (that was quite close what my MS8208 meter gave).

Voltage measurement range covers AC and DC. I did some measurements, and felt that the meter gave very accurate results on both AC and DC ranges. At DC ranges the measurements were very accurate when I compared them to my reference (much less than 1% error). The meter has also mV DC range.

For current measurement at both DC and AC there are several ranges from microamperes up to 10A. The uA range is for measuring very low currents and has series somewhere around 100-150 ohms. The mA range can measure maximum 400 mA with series resistance of around 2 ohms (0.32V drop at 177 mA). This means that at maximum current the voltage drop will be nearly one volt. This range is protected with a 500 mA fast fuse. 10A range very low value (0.005V at 160 mA). At 10 A you are allowed to measure 30 seconds every 15 min. The 10A range is protected with a fuse.

Non contact voltage (NCV) detector is designed to show if there is mains voltage near meter. If mains AC voltage is detected the meter turns on RED LED on the top of the meter display. this feature is always on when meter is turned on. The NCD is said to be designed to detect voltages in 50 – 1000V AC range. NCV reacts typically at 5-15 centers from 230V AC mains cable.

To change battery or fuses it is necessary to open the meter. There is a battery compartment for battery change. For fuse changes the whole meter needs to be opened- The meter works fine and has a good precision. It seems to be a good meter considering the price.

Manual at several languages can be downloaded at https://docs.biltema.com/v2/documents/file/fi/1f8e6f0a-e15c-4c49-a7aa-311e07350e85

Electrical safety

When handling any type of wire or circuit, act as if the power is on. Electricity can be incredibly dangerous. When you use a multimeter, It is important to take measurements in a safe space and use a multimeter suitable for the measurement task. A mistake due to a bad environment or wring type of instrument can damage equipment or kill you. Arc flashes are an explosion caused by an arc of electricity superheating the air. Arc flashes are incredibly dangerous.

The safety of multimeter is depends mostly on meter design itself and the test cables. This meter comes with OK looking test cables that use flexible wire rated up to 2000V. The multimeter side of the cables ends with shrouded safety banana plugs. The test probes feel OK and come with tip insulator that let’s a very small metal tip visible (can be removed if needed). Nothing to complain here.

The CAT rating determines what equipment the multimeter can safely be used on. The electrical safety for this meter is rated for CAT III 300 V, which means is suitable for measurement in distribution networks and normal industrial environments provided that the voltage rating is high enough for the measuring task. This means that this meter is suitable for measuring single phase 230V mains circuits. CAT III meters are approved for use on distribution circuits. Distribution circuits include distribution panels, load centers, and feeder circuits.

The meter is also rated for CAT II 600V, which means that the meter could measure up to 600V on appliances, portable tools, and other household loads. This multimeter seems to have proper construction for the operation at those voltages. There are properly rated ceramic fuses that can safely cut high currents (many kiloamperes) at up to 600V AC and DC. It looks that this meter would safely burn the fuse in case of severe overload or measurement mistake (and not explode like some cheap meters with high current short overload). The downside is that new fuses are somewhat expensive and hard to find parts if you happen to burn them for any reason. It is not a good idea to replace the fuses with other type of fuses for your own safety (multimeters with fuses that are not right type can explode). With right type of fuse this meter looks and fells safe.

Look inside

Who manufactured this meter?

Biltema does not normally manufacture their multimeters themselves, but they buy them from some manufacturer with their logo printed from it.My old Biltema meter from 1990′s wad manufactured by Mastech. This 6-in-1 meter looks like it could be made by CEM or PeakTech.

CEM DT-61 industrial digital multi-function environment meter is 6-in-1 meter. The built-in multi-meter, NCV (Non-Contact AC Voltage) indicator, Sound level, Light, Humidity and Temperature measuring functions replace meters worth over $500. The digital multi-meter function includes ACV, DCV, ACA, DCA, resistance, capacitance, frequency, duty cycle, diode and continuity tests. The specifications looks pretty much the same. This CEM DT-61 seems to be sold out in many places, and at manufacturer page seems to be replaced with DT-61H. From earlier experiences with products from CEM, they have been from OK to a disaster.

PeakTech® P 3690 is a digital multimeter that combines the properties of the most common 4 environmental measurement functions. With the humidity and temperature measurement any ambient temperature, which can influence the measurements of some devices, can be measured and recorded at any time. The PeakTech 3690 is a regular multimeter with functions such as voltage measurement, current measurement, resistance measurement and many more. The manufacturer says the meter is rated CAT III 600V. Otherwise specifications looks to be same.

Any repair tips or recommendations for a good replacement (I want one with light and sound measurement built in).

Tektronix TDS 210 and TDS 220 Digital Real-Time oscilloscopes offered at them time good bandwidth, automated measurement features and analog-like ease of use, at a cost comparable to analog scopes of equal bandwidth. The models differ only in bandwidth. Tektronix launched first the TDS210 with 60MHz bandwidth and backlit monochrome 4,7″ LCD (320 x 240 px). It was like a basic digital oscilloscope where CRT display replaced by LCD, which made the device small and light (1.5 kg).

Key Specifications

Bandwidth	100 MHz (20 MHz at 2 mV/Div and 5 mV/Div, 20 MHz at 10 mV/Div in Peak Detect mode)
Sampling rate	1 GS/s
Sweep	        5 ns/Div to 5 s/Div
Record Length	2,500 sample points per channel
Deflection	2 mV/Div to 5 V/Div, 1-2-5
Resolution	8 bit (256 levels over 10.24 vertical divisions)

Sensitivity (with calibrated fine adjustment): 2 mV to 5V/div (bandwidth limited to 20 MHz at 2 mV/div and 5 mV/div, in all modes, and 20 MHz at 10 mV/div in Peak Detect mode).

Is Tektronix TDS 220 good scope?

If you are used to today’s oscilloscope standards, TDS220 is quite poor. It has no USB, no FFT and no color LCD. It was released back in 1997. The screen on the TDS 220 is not very good. Many people have reported bad BNC connectors issues with it: the BNC connectors are fragile, they break the mounts to the PCB. The TDS 220 has one BNC connector that is broken (but I got it “DIY fixed”).

TDS200 series are pretty much the most basic digital scope you can get. They’re a very basic DSO, much outdated these days but still quite usable if that’s all you need. They perform very bad compared to anything more recent digital. Don’t expect too much in terms of record length as it only offers 2.5K samples per channel here. This is OK for capturing short bursts of serial data but hopeless if you want to capture a long stream of data (use a PC and an external hardware decoder to capture/decode longer streams in addition to this scope).

If you need just basic oscilloscope functions, it works still well for that and is pretty easy to get used to. TDS 220 is quite ideal for simple tasks where you just need a scope for a few basic checks. It does not take much bench space. The user interface is similar to that of an analog oscilloscope.

The plus side is that it is totally silent, takes up very little room can be easily moved around and the user interface is fairly intuitive. So if you like working/concentrating in a quiet workroom when programming/debugging something like a simple AVR/PIC project then this scope is a good choice. No distracting fan noise!

Tektronix TDS210 Digital Oscilloscope Reviewdown.

Sometimes there is need to be able to transfer measurement data from the oscilloscope to PC. Basic version of TDS 220 does not have communications interface, but fortunately my oscilloscope happens to have the communications extension module installed. The TDS2CM COMMUNICATIONS EXTENSION MODULE provides Centronics-type Parallel Port, RS-232 interface and GPIB interface. With this communications module, the oscilloscope operation is programmable through RS-232 and GPIB ports. Tektronix has TEKVISA CONNECTIVITY SOFTWARE – V4.1.1 that can communicate with TDS 220. TekVISA provides communication with instruments that are connected to the PC via various communication buses. I have tried the commications through RS-232, which feeks quite slow at default 9600 bps and maximum 19200 bps communications speeds.

TDS 220 with communications module provides HARDCOPY CAPABILITY with several Printer/File Formats: Thinkjet, Deskjet, Laserjet, Epson (9 or 24 pin), BMP, PCX, IMG, EPS, DPU 411, DPU 412. The Tektronix OpenChoice Desktop free application lets you capture oscilloscope screen images, waveform data, and settings from a Microsoft Windows computer. Another option is to Oscilloscope Downloading Screenshots using Wintek32 video gives one idea how to download an image from the Tektronix TDS210 to a PC using Wintek32 software.

Tutorial videos:

Tektronix TDS 210 digital oscilloscope (1997)

How to use an oscilloscope TDS210 (1)

How to use an oscilloscope TDS210 (2)

03. Oscilloscope Demonstration gEEch

Manuals:

Overview technical data
https://www.rlscientific.com/documenti/TDS220.pdf

TDS200 Series User Manual
Digital Real-Time Oscilloscope User Manual
https://www.tek.com/en/oscilloscope/tds210-manual/tds200-series-user-manual

This document is targeted to product users and explains operation and/or installation procedures. It may also provide information about features and functions, applications and troubleshooting. This manual applies to: TDS210, TDS220, TDS224

Alternative manual locations
https://neurophysics.ucsd.edu/Manuals/Tektronix/TDS%20200-Series%20Manual.pdf
https://docplayer.net/21114251-Beginners-guide-to-the-tds-210-and-tds-220-oscilloscopes.html

Service info:

TDS200 Series Service Manual
Digital Real-Time Oscilloscope Service Manual
https://www.tek.com/en/oscilloscope/tds210-manual/tds200-series-service-manual
 
This document provides information for technicians to maintain or service a product. Information is given to the module level, and may include product care and cleaning tips, troubleshooting information, adjustments, and how to replace parts. This manual applies to: TDS210, TDS220, TDS224

My teardown and story how I fixed the display to work again
https://www.epanorama.net/newepa/2015/01/29/tek-220-scope-teardown/

TDS220 Oscilloscope Refurbishment: Rotary Encoders & Backlight
https://www.dzombak.com/blog/2021/12/TDS220-Oscilloscope-Refurbishment-Rotary-Encoders-Backlight.html

EEVblog #690 – TDS220 Oscilloscope Autopsy
https://www.youtube.com/watch?v=VZCokbsTwmQ

Tektronix TDS210 TDS220 OPEN
https://www.youtube.com/watch?v=PHB2XC_l7Eg

#273 Tektronix TDS220 Backlight Replace and Restore – 1997
https://www.youtube.com/watch?v=weUSGjzEoVM

EEVblog has some interesting fault-finding information: During the boot-up of a TDS200 series oscilloscope, the frequency at the Probe Comp output terminal changes from 5 kHz to 1 kHz, in discrete steps (rather like a countdown timer). When it reaches 1 kHz, the status screen should be displayed. It should also be square wave. If output is > 1.2Khz, it indicate some power supply failure.

Sources:

https://www.tek.com/en/documents/fact-sheet/tds-210-tds-220-fact-sheet
https://w140.com/tekwiki/wiki/TDS220
http://hades.mech.northwestern.edu/index.php/Tektronix_TDS220_Oscilloscope
http://www.primrosebank.net/computers/maint/tools/scope.htm
https://www.eevblog.com/forum/chat/tektronix-tds-220-good-scope/
https://www.eevblog.com/forum/repair/tektronix-tds220/25/

The HP 54645D (also known as Keysight 54645D) mixed-signal oscilloscope was designed for embedded systems developers. This Mixed-signal oscilloscope focuses on 8-bit microcontroller applications was released to market in 1996. This product was discontinued in March 2001.

It was specifically designed to cost-effectively address the testing and troubleshooting needs of the many engineers designing with 8-bit microcontrollers, but was powerful enough also for many 16-bit embedded applications.

The Keysight 54645D 100-MHz 200-MSa/s Mixed Signal Oscilloscope seamlessly integrates logic channels into an oscilloscope to offer new measurement capability for designers of combined analog and digital systems. Analog and digital on one display, aligned in time, to help you isolate cause and effect in complex circuits.

The 54645D was selling for under $5,000 ($4,995 stock), which was cheap at the time when you consider what features it offers.

The HP 54645D is a two-channel, deep-memory oscilloscope integrated with a 16-channel logic analyzer. It features the ability to trigger on any or all of its 18 channels and to observe and measure the relationship of the analog and logical operations of a circuit under test on a single display screen.

Specifications:

Scope Channels: Ch. 1 and Ch. 2. 
Bandwidth (3dB): dc to 100 MHz @ >= 10 mv/div (> 75 Mhz @ < 10 mv/div), ac Coupled: 1.5 Hz to 100 MHz. 
Rise Time (calculated): ~ 3.5 ns @ > 10 mv/div (< 4.6 ns @ < 10 mv/div). Input Resistance: 1 Mohm. 
Input Capacitance: ~13 pF. 
Maximum Input: 400 V (dc + peak ac). Range: 1 mV/div to 5 V/div. 

Digital channels: 16 channels (0-15) in two pods of 8 channels each 
Maximum Input Voltage: ± 40 volts peak. 
Threshold Range: ± 6.0 volts in 50 mV increments. 
Threshold Accuracy: ± (100 mV + 3% of threshold setting). 
Sweep Speeds: 50 s/div to 5 ns/div main and delayed. 
Accuracy: ± 0.01%. Horizontal Resolution: 40 ps. Trigger Modes: Auto, Autolevel, and Normal. 
Holdoff: ~ 200 ns to ~ 25 seconds. 
Polarity: Rising or falling. 
Minimum Pulse Width Setting: 8 ns. 
Maximum Sampling Rate: 400 MSa/s on one pod, 200 MSa/s on two pods. Maximum Memory Depth: 2 MB samples per channel on one pod, 1 MB samples when both pods are used.

Display: 7-inch raster monochrome CRT. 

The two scope channels of the HP 54645D are each 100 MHz and 200 megasamples/s, and feature 1 Mbyte of memory. The logic-analysis channels run at 400 Msamples/s and 2 Mbytes of memory on eight channels, and 200 Msamples/s and 1 Mbyte of memory on 16 channels.The scope supports simple edge, pattern, and advanced triggering capabilities, including a glitch triggering feature.

Because the MSO is an two channel digital oscilloscope, you works for everyday use with its simple edge triggering. This has the familiar scope triggering mode and it is the one that will solve most of problems that you have with electronics circuits. In addition to analog channels, you can view the 16 digital states and use them as triggering source.
You can trigger on a rising or falling edge on any of the MSO’s 18 input channels. Pattern triggering is provided to allow you to set up a pattern of high, low and don’t-care levels across any or all of the MSO’s 18 channels.

The 54645 was the first of the digital oscilloscopes with MegaZoom so it has 4 megapoints memory both on analog AND digital combined. MegaZoom technology that is a multiprocessor/parallel-processing architecture that enables the HP 54645D to combine the deep memory capability associated with some high-end DSOs with the ease-of-use, high update rates, and responsiveness usually found only traditionally in analog scopes. Megazoom is , apart from the large memory, basically a huge resampling ASIC that resamples the ‘slot’ you define in the memory and creates a 540 pixel wide image to screen. I have to admit that MegaZoom works well.

While the HP 54645D is not the first instrument to combine oscilloscope and logic-analysis capabilities, its ease of use, versatility, and price combine to set a new standard.

Digital Oscilloscope Set Up and Tutorial using HP 54645D Digital Storage Oscilloscope video shows how to set up and use the HP 54645D digital oscilloscope.

HP 54645D Pushed to the MAX! video demonstrates how responsive and capable a vintage (1998) digital HP scope (HP 54645D) is. This video also demonstrates FFT function from the Measurement module (that I don't have).

There is a "easter egg" game in this oscilloscope. It can be started by pressing first "Print Utility" and then two buttons below screen together (buttons 2 and 3 from left to right).

You get this snake game:

Another hidden feature:

HP 54645D Manuals
https://www.manualslib.com/products/Hp-54645d-2960596.html

Keysight product page with manual downloads
https://www.keysight.com/us/en/product/54645D/100mhz-200msas-mixed-signal-oscilloscope.html

Sources:

Mixed-signal oscilloscope focuses on 8-bit microcontroller applications
Posted on January 1, 1997 by Electronic Products
https://www.electronicproducts.com/mixed-signal-oscilloscope-focuses-on-8-bit-microcontroller-applications/

Old logic analyzer and probe cables
https://www.epanorama.net/newepa/2022/07/05/old-logic-analyzer-and-probe-cables/

Keysight (Agilent) 54645D CALIBRATION and Keysight (Agilent) 54645D REPAIR
https://custom-cal.com/ModelInfo.aspx?kn=3465&m=Agilent_54645D&srv=Calibration

54645D 100-MHz 200-MSa/s Mixed Signal Oscilloscope
https://www.keysight.com/us/en/product/54645D/100mhz-200msas-mixed-signal-oscilloscope.html

Should I sell my 54645D for a new Rigol?
https://www.eevblog.com/forum/testgear/should-i-sell-my-54645d-for-a-new-rigol/

HP54645D print screen via RS232
https://www.eevblog.com/forum/testgear/hp54645d-print-screen-via-rs232/

Playing Tetris On An Oscilloscope
https://hackaday.com/2014/04/26/playing-tetris-on-an-oscilloscope/

Oscilloscopes have been invented in the 1920s. Up to now this instrument encountered many innovations.

Today the main players are Keysight, Tektronix and Teledyne LeCroy.

Read more at: http://www.oscopes.info/background/2265-oscilloscope-milestones

The Tektronix 2235 is a 100 MHz dual-trace, dual-timebase portable scope.
Tektronix 2235 has two channels and delayed sweep.

This is still a pretty decent analogue oscilloscope (if you are looking for an analogue oscilloscope) with Large, Bright CRT screen. This oscilloscope has the U shaped handle that has detents which allow it to double as a stand.

Tektronix 2235 100 mhz Oscilloscope- When Only Analog will do….

The manufacturing of this scope model started around 1983 by Tektronix, Inc. In 1984 the price was $1,650 ($4,300 in 2021 dollars). It was also sold to the military under the model name AN/USM-488.

It was then advertised with features like: Tektronix 2235 ensures measurement quality and reliability while reducing instrument cost. Tek started with the innovative architecture of the 2200 Series: fewer boards, fewer mechanical parts, less cabling and electrical connectors. This approach, plus advanced circuit design and a focus on essential features, has led to a scope that is more accurate, more reliable, lighter and more serviceable-and simpler to use-than any other 100 MHz scope. Features like rugged design, light weight and easily learned front panel make the 2235 an ideal service scope.

The 2235 delivers 2% vertical and horizontal accuracy in normal operation. Accuracy of 3% or better is maintained across a wide range of environmental extremes.

This oscilloscope has 100 MHz bandwidth, which is a quite good bandwidth and also the vertical voltage goes down to 2m volt. With oscilloscopes like these, Tektronix specifies the bandwidth at the probe tip when the proper probe is used. The quoted bandwidth is given at -3dB (http://www.ens-lyon.fr/DSM/AGREG-Physique/oral/Notices/N036-003.pdf) to be (at least) 100 Mhz from 5mV to 5V/div and 90 Mhz at 2 mV/div… And it also deacreses by 10 Mhz when the ambient temperature rises above 35 degrees celsius. If you can accept some measurements errors, you can do some measurements event at higher frequencies. The 2235′s 100 MHz will cover enough above and beyond 108 MHz if you have probes that will go well above 100 MHz.

The input capacitance of this oscilloscope is around 20 pF.

You also get delayed sweep with the 2235. Delayed sweep is a technique that adds a precise amount of time between the trigger point and the beginning of the scope sweep. When the scope is being used in the sweep mode, the start of the horizontal sweep can be delayed. In some applications it can be useful, but you probably won’t end up using much.

The calibration adjustment are done with pots, that can change their position slightly due to mechanical vibrations for example. Service manual is still available on-line.

Manuals:

2235 Oscilloscope Operators Instruction Manual
https://www.tek.com/en/oscilloscope/2235-manual/2235

2235 Service Manual
This manual contains information to check performance, adjust, and service the 2235 oscilloscope.
https://www.tek.com/en/oscilloscope/manual/2235-service-manual

Tek Wiki 2235
https://w140.com/tekwiki/wiki/2235

Videos:
Tektronix 2235 – 100Mhz Dual Trace, Dual Time Base Oscilloscope
Affordable Portables Tektronix 2200 Series Oscilloscopes 1986
Tektronix AN/USM-488 2235 Oscilloscope repair and calibration 1 of 7
Tektronix AN/USM-488 2235 Oscilloscope repair and calibration 4 of 7

Links to sources and more material:
https://www.computerhistory.org/collections/catalog/102733015
https://www.eevblog.com/forum/testgear/tektronix-2235/
http://www.linear.com/docs/4138
http://circuitslab.case.edu/manuals/Probe_Fundamentals-_Tektronix.pdf
https://www.antiqueradios.com/forums/viewtopic.php?t=147362
https://www.testequipmentdepot.com/usedequipment/tektronix/oscilloscopes/tek2235&2236.htm
https://accusrc.com/product-Tektronix-2235-3929