#324 

You don’t need a metrologist’s approval lol, your approach is rock-solid (I’m a Lead Metrologist at a NASA Electronics Cal Lab, 26 years now). We don’t see 260s coming through anymore, I miss the analog stuff. We’d just use a Fluke 5522A or newer calibrator for a 50uA source. No fun in that! Late to the party but enjoyed your presentation! 73

I just obtained a mint condition 260 series 5 which is in need of calibration. This video is excellent and exactly what I needed. Thanks for posting.

I just made one of your 50uA current sources. I don't have a micro-ammeter, but I do have an HP 3456A. So, when I created the board with kicad, I added a 2K .05% precision resistor across the 50uA output through a 2-pin header. So, connect the header (i.e. the 2K resistor), set the output for 100mV, disconnect the header, and you have a pretty good 50uA current source. By the way, while fiddling with this, I discovered that my Sperry handheld DVM is only 20uV different from the 3456A when measuring 100mV. So, you don't need much more than a handheld DVM to calibrate your device, as long as you have a high precision 2K resistor to set the pot for 100mV. Well done, by the way! This is an easy way to rehabilitate an old Simpson 260 and be sure the meter is pretty much spot-on.

I use a variac and a stepup transformer to get the 250VAC. Used variac and 6V trans for the 2.5 but forgot about my function gen. Thanks!

Thx for taking the time in making and sharing this video. After having a 260 6P for about 8yrs I ran it through a cal cycle in a cal lab that I worked in. It hit all the numbers, well withing spec. That was 1983. I recently pulled it out. It seems to still have excellent calibration. What a stable design. As for accuracy. If you are careful in calibrating these meters you'll get surprising accuracy and precision. A lot of the dig meters have around 1% DC specs worser on AC. That means you are only getting 2 digits of accuracy not 3 1/2. The low cost meter guys are chumping you and you don't even know it. That's why you need Fluke quality they give you specs that can support the number of digits the meters display. Sorry, I digressed. Back to the Simpson. If you can discern 122V you have 3 digits of accuracy. Not bad since a lot of digs are worser. So, don't poo poo an analog meter too readily they have more accuracy than you think. Again, thx for sharing this video.

Thanks! Just finished repairing and calibrating my hamfest simpson 260 series 7!

Hi Alan, You've done it again with another great video. Happy Holidays to you and the family. Stay safe. 73 WJ3U

Great job including the disclaimers! I did work in a cal lab back in the 1980s. We had a lot of 260s in our company. We always calibrated them in the upright position, because that's how they were used by most of our techs. They were mostly used as continuity checkers anyway, since digital multimeters had pretty much taken over by then.

Wow, this is perfect timing. I just found an old 261 and thought that it was hopelessly out of calibration. I will be sure to try this. Thank you!

Thanks Alan, for another clear and informative video, with an added bonus - loved that 50uA current source :-)

Another great video -- always learn something new!

Thanks for the great overview of the current mirror and its application for the calibration of faithful and reliable Simpson's VOMs. I recently gave my 260-8P to my nephew and I currently using a 270 Series 5. Strange, I had just calibrated my 270 a few months ago and used some to the same resources that you have listed.

Thanks so much for this and all your videos. This one for me was just perfect timing. I recently purchased a 270 series 4 in need of some attention which is very similar to the 260 series 6 from what I can gather. After basic maintenance and replacing the usual flaky resistors that were overcooked on the r1, 10 &100 I have just started tinkering with calibration of the dc voltage & amperage when this video came up on my feed. Saved me a lot a grief but also verified I was on the right track. Always learn so much from your channel. Keep up the great work and happy new year,

Another excellent video.Your teaching skills are first class!

Thanks for the tutorial Alan...have a 5P and 7M to calibrate and your tips will make the job much easier! Happy New Year! DE KLØS

Your videos are always quite good. Have learned new info for electronics from your lectures. Thanks.

Thanks dr Alan. This will help me a lot when aligning my own 260 Model 7M

Good stuff Alan, thanks for this demonstration and the associated links and notes.

Thanks for posting this Alen. I have a series 2, 4, and 6 and while I don't use them much, having them is good.

Good video - I was here for the 50uA current source. Since I did not have a zener, I modded your circuit a bit. I used a red LED (Uf~=1.7V) and only had to remove the 91k resistor (and I also used a 10k pot). Works well, maybe not as stable as yours, but it was a bit easier to build.

Thanks, Alan for another great video and detailed information on the Simpson 260 calibration. I bought a 260-7P over the summer on eBay and just did preliminary comparison measurements to my bench GW GDM-8135 DMM and my Fluke 87 DVOM and it is close. I wanted to perform a more thorough calibration myself without sending the meter out and now I can with your ingredients.

Excellent video as always. Thank you for sharing your knowledge.

Thank you Alan. You always make things so clear that it encourage me to try and replicate your work. I have a new Simpson 260 but now I want to calibrate it!

Great video. I used a 250 mV source and bench multimeter measuring current to calibrate mine. A little bit of back and forth, between R2 and R27, but since I only own one 260, it was faster than setting up a current source. The one I bought had a battery leakage, which was messing up the readings at the higher scales, but after a vinegar, water and iso alcohol bath it was back in the game. Really sturdy meter!

I need to get back into relearning electronics. I always love your videos.

You're very good calibrator explaining everything.

Great video. Was a cal tech when i was in the service around the mid 80's. All what you said was true. It is the standards that are the key. Following the cal procedure was easy . Basically just follow the list and meet the results and that was it

Alan, Thank You for providing this Simpson 260 calibration detail, greatly appreciated. Chuck W9KR

Excellent as always. Thank you!

Wow that was great Alan, thank you so much. I do have a real nice 260. A series 2PM so I will check the schematic as well before I do this cal. Thanks for sharing.

Thank you for very valuable information about Model 260, I have three of these instruments and they are in mint condition, 73 the SM4PDP

Thanx again for your insights.. today my son & I "breadboarded" the 50 microamp source, from parts I had (some things aren't exactly your spec's i.e. 6.2v Zener etc...but close enough).. Any way what we found.. using a fresh 9v battery the resistance req'd for 50.0 microamps is 93Kohms.. your design 91K w/ 5K pot is perfect, even with the 6.2v zener. When I used an "old" 9vdc 400ma P/S (from who knows what appliance it used to charge).. we couldn't get 50microamps until we lowered the "resistance" to 63Kohms... So the mod we made.. a 51K replaces your 91k, 100K pot and 5 K pot series give me a variable range of 51k (or so) to 156K.. so I can use either a battery or my wall P/S, and the 5K pot makes for fine control.. In practice I cal'd / checked 4 Simpson's, another (odd ball) meter has a 80microamp movement...turns out I can get there... -->next on my list.. make a mod to get me down to 10microamps.. that is what my 269-2's meter movement is.. That all said THANX again for the insight and giving me a project...Once the design is final.. it will be time to solder it all to a PCB..

Very nice! Thank you for you time and effort.

valued information...well done!

Excellent explanations!

Modern DMM Calibration Procedure: 1. Connect precision source. 2. Verify DMM meter readings. 3. Generate Certification Paperwork. 4. Charge Customer $150.

Many thanks for the nice demonstration.

As to the 250V AC calibration, you could use a couple "filament" transformers (there I go dating myself again), connected secondary to secondary to obtain it. 120V mains in --> 120V to 12.6V xfmr --> 6.3V to 120V xfmr --> ~240V out (i.e. connected in --> P:S --> S:P --> out). Added advantage of this approach is isolation from the mains will provide some equipment and shock protection if implemented correctly. Of course, the usual disclaimers regarding high voltage safety apply. You should only try this if you are properly trained and qualified, and fully understand and accept all risks involved. I accept no responsibility for any results or outcomes you may obtain.

Thanks Allan, Interesting video :) ATB Adam

Best stuff as always.

Thanks Alan just what i need. I have 2 of them the 260 - 6 and the Model 260-6XL they need calibration.

Thank you Alan.

Thank you so much for the video.

Great video as usual. Would be great with an "In depth" video about the current source.

Great video Alan, as a former (now retired) I can say all of your disclaimers were correct and appropriate. It’s ok to “check things out” the way you did, but traceability is required for validated processes. My comment is on one technique mistake you made when you used the 122 line voltage as your test point for the AC adjustment. You can’t make an “adjustment” to a point that doesn’t exist on the scale, thus “eyeballing” it somewhere in between. Bzzzzzzzzzz no good! Hi! You must somehow generate 120 or 125 so that adjustment can be made to these ticks that DO exist on the scale! In the real world what you did is fine for your’s or my shop use. But you asked us metrology types to chime in on what you were doing.

Great video! I presently have three 260s and they will all benefit from a calibration. I specially liked the inclusion of the 50 uA current source circuit: I will be building one. But you neglected to say how the 5K adjustment is set. I guess I just need a good current meter or a precision resistor with a good Volt meter. Thanks for the information. It WILL be useful.

I'm assuming taking the 250 mV reading is when connected to the common and the 50uA plugs and not internally on the circuit board. While the full-scale 50uA is being applied of course. Didn't have the exact components for the Wilson current mirror so I cobbled the circuit together from what I had available. The 50 uA span adjustment was almost at the full range of the R-32 pot. I do like to have pots nearer to mid-range when tuned/calibrated. Thx for the video, 73 Alan!

My Simpson 260 Model 8P thanks you! It's probably due for a touch up.

Great series on the venerable 260's Alan!.....I see a presentation in the future!? ...NJARC

Was wanting to align one of my 260's and wondered if there were any YT videos to use as a reference. BINGO !!!. Tnx Alan es 73 de WA4AOS dit dit

Good video

I tried building this current source. I used two zener diodes, a 6V2 into a transistor that provides constant current for a 5V1, for shits and giggles. The double setup actually seemed to make it extremely stable over supply voltage changes. 7->12V wasn't very noticeable. I tried using an "improved wilson current mirror" that uses a 4th transistor. Arbitrarily I used 5.6k degeneration resistors, and simulated it in Falstad to get rough resistor values needed for current setup and trim. I decided I wanted both 50uA and 10uA source, so had a DPDT switch to go between them. After a lot of faffing around getting the trim in tolerance, I finally had it set up. Seems to wonder around quite a bit, I wonder if that's from temperature variance of all the BJTs diode drops? Not sure. Maybe there's a huge tempco I can trim down with something else in the future. I am kind of curious whether the 4th transistor helps a lot or not, or if it's possible it even hurts the circuit.

Awesome - I have this meter! Series 8

Is it possible to use DC voltage for the AC calibration ? Remembering to adjust for 0.7 (rms) of the dc voltage and not peak of course.

Nice

Thanks for the video, especially the bonus current source! I think I'll make one. I don't have a Simpson meter, but I do have some 50uA panel meters, and I'm interested in the varistor protection device. I didn't see a part number for it in the linked manuals. Do you know anything about it?

A quick note on adjusting a meter's zero: Turn the adjustment screw clockwise until the meter reads zero the turn the adjustment screw counter-clockwise just enough so the screw's cam is no longer touching the adjustment fork.

I had to use a regulated low voltage supply and a decade resistance box to set the 50 uA. But the mil cal calls for adjusting the other pot for 1 mA on that range. In any case it then reads a small amount low on DC readings after the mil method. I will try the 50 uA 250mV method. I have seen Simpsons that read dead on for DC so I know they can do it. The later meters use good Dale metal film dividers but some of the old ones used those black resistors and those can change value a small amount.

I see that your are using Manhattan style PCB. The pads appear rectangular. I have found a pad source from a QRP site but there are square in two different sizes. Where do you source your PCB rectangular pads ? I just bought a 260 at a yard sale and looking forward to using you cal procedure when I get some 2N3906 transistors delivered. Thanks, great channel.

For the 250mV adjustment, did the calibration info specify the meter input impedance? Is the keithley 10MOhm or is it in the GOhm’s in that scale? The input impedance could have an effect on the accuracy of that setting at those low voltages and currents. The calibration may have been expecting a 1MOhm or 10MOhm load from the meter, which is why I’m asking, because if the Keithley was in the GOhms it might have resulted in an incorrect adjustment (counterintuitively)

Merry christmas Nice video thanks for posting I want to ask you do you have the heathkit hm- 102

Just a slightly off the main topic note. Some people may not know or realize that they probably have a 1 mA constant current source in their DVM. If it has a diode test function, it has the 1 mA constant current source. It appears to be an "industry standard" that the diode measurements are made at that current. The maximum load varies, but I have mostly seen a bit over 2 V, which relates to a usual desire to measure silicon diode voltage drops (about 0.6 to 0.7 V for small diodes and less for huge ones). Anyway, suitable for common DVMs that have their voltage full scale 1.999 V. Of course 1 mA is not good for the need of 50 uA constant current!

Thanks. I noticed you used Wainwright for prototyping - my favorite method. But I've not found parts for years and years. Did you find a source or are you depleting your junk box inventory as I am?

Alan, great video. I need to go back and check calibration to my dad's unit again now! 😬 Wouldn't the dmm to measure voltage in parallel with the meter affect the reading. Yes, I know, a 10Meg or higher in parallel with 5k won't affect the result, but, the effect is there.

Excuse me friend, as calibrated the simpson 260-7 galbanometer of the stall of the needle travel, it only starts well in the position in horizontal or in some position of side. Thank you for your attention

Thats why I'm here Too learn and relearn

Again I have to start by saying I love your videos. We previously spoke via your meter shunt video... Anyway, I have created your 50 microamp device in a small project box using a 9V battery or a 9V input. It works wonderfully. For the 5K pot I used a precision 20 turn pot and this device is never of more then a few 100th of a microamp which are easily dialed in with the pot... I was wondering what I can do to make it variable across a range say from 25 to 250 Microamps... Would both of the 10K resistor need to be modified to be some kind of double pot? Or is the voltage drop across the diode the key to this circuit and that leg would need to be controlled somehow. Any insight would be great. In regards to the calibration I have two 260s. My series 6 is spot on and the teency tiny bit it is off its not work messing with. The series 7 seems to have an issue that is not just calibration. First of all once I turn it on the needle moves positive of the 0 and in resistance I can't get it to full scale. I can't zero RX1 either yet the other resistances do zero. When I check a voltage, which is off the needle will move to a max position then start to drift low as if a cap is discharging. I'm not sure I'm going to focus on that one at the moment. I did use your video to procure the sleeves to address the reverse banana but I really don't use this one. These are reminiscent of my days in the Navy when this was the standard issue VOM. Yes I was in the Navy before DMMs were in use. Again thanks for your videos... I'll have a few questions soon on your Sweep video...Thx, Ben

Nice presentation, just one question regarding the 50ua current source. How is the 5k trimmer used to set up the output current?

Thanks Alan! Is the 1N4577 Zener critical? Or can it be substituted for something like a 1N4571? The 1N4577 is a bit pricey and DigiKey forces you to buy in bulk whereas the 1N4571 is a bit cheaper and can be bought individually.

Alan, is the 6.4 volt zener essential? That is, could a zener of similar (i. e., closer) value be used? For example, I have 1N4743A (5.6v) and 1N4725 (5.1v) zeners. I assume the trim pot is for current adjustment.

Alan, I apologize in advance if you have answered this question already. What brand smart notebook are you using is it the Rocketbook, and do you like it?

A question: I have been working on building your current source circuit and have found that the 1N4577, 6.4V Zener diode is both hard to find and expensive. This diode is described as temperature compensated and seems to come in 5% and 1% tolerances. That makes me wonder if the 6.4V rating is a critical value (most Zeners come in tolerances of 5%, 10%, or even 20%) or can I substitute a more common Zener value, like 6.2V at 5%? For instance I already have 1N5233B which is 6.2V, 5%. Will the 5K pot compensate for that value?

Hey I recently found your channel. I was wondering what field do you work in? I am a metrologist, formerly air force now contractor. Work mostly electronics these days (k1,k3,k4,k8).

Could you drive a transformer with that function generator to get 250VAC?

would a bc557 work in place of a 2n3906

Another Winter project for my Series 5, 6 and 7! Can you do a Triplett 630 next? Thanks!

What is P05 V0I S0000000? (The QR Code decoded)

Does the digital version need calibration too?

you can help me ? i can't calib to zero on x1 range ohm.what i have to do ? hope you help me.Thanks

Can you repair baklite, I need to patch one?

For anyone panicking over the DMM measuring the 0.25 V DC and shunting the 50 uA: Input Z of that DMM is >10 Gohm

I don't understand why you set the 2.5vac on your function generation output impedance to "high impedance Z" because a simpson 260 input is not High impedance Z its not a digital fluke DVM meter it has loading issues. I'm not sure what the simpson 260 AC input loading impedance is but I don't think its high impedance Z. Also what is that bridge called with the diodes and resistors for adjusting the AC trim pots in the bridge for the AC voltages? does the bridge have a name?

🙏🙏🙏❤️❤️❤️🙏🙏🙏

I learned there is such a thing as a "Metrologist" !

I wanna share it to the world.....I kinda feel if they want it, they'll find it!!!

As is your trademark make it simple.... . but...These videos make me ask....Why is it we "electronic nerds" don't just have 1 Simpson 260 (et al) but 5 or more, not 1 DMM but 5 or more?

What's with the goofy disclaimer? Most anyone using, or familiar with calibration of these meters are in a rest home or a collector.