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- เผยแพร่เมื่อ 6 พ.ย. 2016
- I bought a used Heathkit model IM-18 Vacuum Tube Volt Meter (VTVM) on eBay and did repairs and calibrations necessary to bring it up to full operational status and "factory" specifications. Along the way, I got an alternate set of VTVM test leads, replaced some worn components, and 'hacked' the circuit so the Ohmmeter battery is no longer required. In the video, I cover all aspects of the project. I especially think that my hack of the simple battery eliminator, although not an original or unique circuit, will be helpful to others. I included not just the final design of this hack, but also the thoughts and experiments that led up to the final design.
- แนวปฏิบัติและการใช้ชีวิต
Excellent video and attention to detail. Really enjoyed the on-the-fly analysis. Also, thanks for showing your battery eliminator steps. I've seen others constructed with perf board but I have a bunch of old terminal strips and really like how you showed both the 3 and 5 lug connections.
Many thanks for posting this. Just completed this mod on my 1974-vintage IM-28, and it worked a treat!
Nice video! Very concise and informative without the annoying fluff like so many other posted vids on Ytube. Thank you!
Had one of those for many years, still have it and decided today to get it working again. Junk parts from my desk, one trip to the shop and works perfect. All I had on hand was 2200 MFD @ 50 V so figured why not? Scope showed almost no ripple, put it in and as I said, perfect. Your video inspired me to fix this thing after 20 years and thanks for that. Now it will be on my bench. Again thanks, Glenn AKA electro
Great video. I did this modification to my own VTVM, only I went with a full-wave rectifier, a single 1.5V Zener diode for the regulator and because the ripple was less this way, put a 1W dropping resistor in. Seems to work. Same amount of components but with a cleaner DC voltage.
Excellent video on the IM-18/28 VTVM circuit and the battery eliminator.....I just built it and it works GREAT.......measured 1.522VDC @ the ' + ' side of the circuit. I'm ready to install one in my IM-28 (bench model).........tks ! My IM-18 is well over 40+ years of age and is still kicking ! ! ! !
This is an absolutely magnificent video! Not only for the development of the battery eliminating circuit but also for your stumbling through the calibration procedure! That's not meant to be disrespectful by any means. You have memorialized in your video the solution to a number of problems I always encountered when breathing life back into these beasts. (I own a Heath V7A that was the best of a collection I had a while ago.)
While I prefer to keep a battery in mine - they actually last a long time - the computations done to develop your circuit is a superb demonstration of design considerations and the math involved. I just put a stern, dated warning sticker on the front of my meter. All in all, I am sincerely grateful for your efforts!
Thanks for your time and knowledge
I have the same meter coming in the mail. I'm sure to perform this test and mods first thing after I get on my bench. Thank for Your Efforts !
Thanks for spending your time on this video
I think one of Mr. Carlsons Lab videos has a solution in it for balancing the zero points.
Per the original NBS (NIST) VTVM calibration standard, that is one of THE most important measurements, and if at any time it does not zero after a calibration step has been completed, that entire step needs re-doing.
I have done this on several VTVMs that I've restored. The following has worked fine for me.
Same as you, diode and small cap then into an LM317 regulator controlled with a 240 ohm resistor and 1k trimmer. A couple of .01uF thrown in to keep it quiet. You can get as low as 1.2 v output. A little heat sink on the 317 to keep everyone happy. This works for 1.5 and 3 volt machines.
Another way, although less accurate, might be to use your same starting point giving 7 vdc, then just add a string of 5 or 6 diodes to end up giving just under 1.5 or 3 volts. Would have to play with different diode varieties with different voltage losses. Puts almost no load on the filament winding.
Thanks! I just drug one of these home from the antique store yesterday. I'm going to change both of the capacitors inside and try to just use a C cell for now or not bother with ohms. I was wanting a VTVM to service old CB radios by the Sams Photofact catalogs. I did end up getting an IFR service monitor with a good AC/DC volt meter built in so I don't need this, but it's still fun to have around. The price I paid was half what the 12AU7 tube is worth, so I'm happy.
That Probe kit is nice and very complete. I have one of mine equipped with them.
Very good video, lots of attention to detail! Thanks! Take Care--Larry
Nice handi-work with good layout.
Very nice Video! I enjoyed it. Nice shop and work bench!!
Hi, nice video, I just finished restoring one I picked up. Re: Battery Eliminator. FYI The Heathkit IM5228 was the last bench style VTVM from Heathkit. It showed a battery eliminating circuit on page 8 of the manual using an LM-317. When Heathkit (Daystrom) was acquired by Schlumberger Limited another VTVM came out the SM-21A (link to a photo below, (I mention this as someone will comment that the IM-5228 was not the last one made) ) The IM-18 the one in this video is basically the same as the IM-13, 28 and the others mentioned here. The A.C. Coupling cap is easy to swap out. Just take off the knob and nut holding the selector to the face-plate. With the circuit board lifted up and the selector pushed away from the face-plate the capacitor is easily replaced. I do have a question for anyone. If I remember my Vacuum tube technology the first number on a tube (USA) is the filament voltage. So a 12AU7 needs 12 volts and a 6AU7 would use 6 volts. D.C.. Therefore in these VTVM's why are they using 12AU7 when the filament voltage is only 6.3 DC? In very early VTVMS like the "V2" a 6AU7 tube was used, same basic circuit. Thanks.. Here is the link for the Heath/Schlumberger meter. www.nostalgickitscentral.com/heath/products/test/sm21a.jpg
Tom Heckhaus, I had considered using a linear voltage regulator IC to provide the 1.5V required to be a battery eliminator. But I still needed a rectifier and a filer cap, so adding another couple of diodes and a resistor seemed like a better option. Also, a linear regulator would be dropping about 5.5V or thereabouts, and would have run a bit warm. I liked the idea of the method I selected, but I know lots of other people have used linear regulators instead.
Tom you may have forgotten than any 12a_7 tube's filament has a center-tap, so it's really two 6.3v filaments in parallel, or one 12.6v filament when they're conected in series. The Heath VTVM's use them in parallel, hence the need for only 6.3v.
I built one of these things as a kid and never really understood it. Got a BSEE 5 years or so after tubes had become irrelevant in state of the art electronics 0- meaning that I am mostly a transistor man. Recently I have taken an interest in the old valves and this was both fun and interesting and educational. Thanks. But looking at your schematic I noticed something about the ohms resistor network. If my google images are correct then the maximum load on the battery is 1.5 volts across 9.1 ohms or 0.165 Amps. This would be (more or less) the maximum current draw through the dropping resistor in the battery replacement circuit. Being conservative, 6V - 1.5V = 4.5V across the dropping resistor, drawing 0.165 amps max, implies a resistor of no greater than 27 ohms. This would necessitate a .75 watt resistor to be sure. But higher dropping resistor and the voltage across the two 4004 diodes may drop below the 1.5 they are expecting, and adversely affect the measurement. While this does not feel right the numbers do seem to check out. Have you checked to see if the voltage across the two diodes is 1.5 Volts when you are measuring 0 ohms on the lowest range? I'd be interested if for no other reason than to see if I "still got it". In any case, great vid.
Cool video. I had no idea you were into electronics too, lol. I've watched your Amtrak Odyssey series on the Cardinal. I have an old De Vry VTVM myself.
Excellent video !
Just found your video, so I had to pull out my IM-18. Built it as an electronics project back in 1969. On mine, the meter bulb is not for illumination, but has a red lens and just indicates power. Also, my ohm setting works on AC power without a battery in the holder. From what I recall, I never used it with a battery. Am I missing something? I plan on replacing the main cap and performing calibration. Thanks for the detailed video.
Bob, are you sure that you have the same model and not a similar looking one? Are you sure that on the Ohms setting that the meter is really working correctly, and not simply moving the pointer? In the IM-18 circuit, the battery provides the current that passes through the resistance under test, so you should not be able to truly read resistances without the battery. Or perhaps yours was modified at some time, or built using a battery eliminator, and you just forgot over the years?
I suggest going through the entire testing and calibration process from the manual, to see if everything is actually working properly.
One thing I noticed about the original plug is that the insulation ring is quite a bit wider than the replacement plug. It might be possible for high voltage to jump that gap, if you're trying to probe voltages in a high-voltage tube power supply or other similar high-voltage source.
Hello - Really great video and modification. I have the same model and need to carry out the battery elimination modification. Your video is of invaluable source of information. Just wondering what would be the effect of having a mains grounded lead instead of the two wire lead used by Heathkit.
i used the im 11 for 50 years along with a simpson 260 in the last 24 years . the heathkit was recalibrated after digital meters came out. it is still as good as any meter i own it is very close to a fluke 70
The specifications on any Heathkit VTVM are nowhere near as good as practically any DVM, often no better than 5%. Not bad for what it is, but the VTVM will never be as accurate as a modern digital meter.
My im11dims sorry for any conflct
It won't match today's Fluke handhelds, but it's certainly more than sufficient accuracy for 99% of circuit applications hobbyist mess around with.
Do you think you could add a BNC connector to the meter, then use oscilloscope probe's...? They usually have a straight thru wire, and a switch that puts a 10 meg ohm resistor in line..
Good idea! The BNC is a better connector to use. The scope probe is clever as long as it is a direct connection. The attenuators in a scope probe re caps and will prevent the D.C. And Ohms no path of continuity.
Excellent video. I have an IM-18 VTVM and want to do the battery replacement. I want to do a full wave bridge - just don't like the ripple. Do you think I am being too obsessive?
Ronald Scott, the ripple is insignificant, and the meter movement would damp it out anyway.
Got you.. Thanks again your video is a great tutorial!
I have the Simpson 270 series 2 meter..and love it..
I've got the Simpson 260 from 1965. I never left batteries unattended in it. My bench meter is the RCA WV-98 C, a real work horse. All VTVM' 's use the similar circuitry , only looking physically different. I've had a Knight,
kG-620 and Heathkit IM-13, plus the EICO 232 and 224, but sold them to buy the RCA WV-98.
A #47 is also a popular bulb...ususally used in radio dials..and they are bayonet mount
bayonet mount #47 compatible LED bulbs are available. Probably a lot brighter than the bulbs. Ordered a couple from China via ebay, for a Heathkit VTVM and a 1960 reel to reel I'm fixing up. Under $2.
I have an IM-18.... i bought the same replacement probes, thanks for the tip...
My meter works for measuring ohms (with a fresh battery installed for now)
But i get nothing on the dc and ac ranges, the meter doesn't budge.
Any idea where i can start? :)
You can download the IM-18 manual from several places on the internet. It has troubleshooting information. The circuit is pretty simple, so not a lot of parts to go wrong. My guess would be that maybe there is an open contact somewhere, possibly in the rotary switches. I had similar issues with my IM-18 when I first got it, but I applied so contact cleaner to the switches and exercised them back and forth a bunch of times, after which everything worked.
Check the tubes first after you clean the contacts.
I bought from Ali express L.E.D.Bulbs for mine I haven't used them.yet because I also bought a box of standard volt one for my three meters ,But I thought the L.E.D.would last longer and you can get them in white or natural light 6volt bulbs screw base ,I found you don't really need that black sleeve for them either
just a note that 12AT7/12AV7/12AZ7 are adequate substitutes for the 12AU7 . 12AU7s are getting expensive and 12AV7 or 12AZ7 can still be found NOS at low cost
I use a better quality triode in my RCA WV98C VTVM, replacing the 12AU7 with a 12AX7, it gives better frequency response with slightly less gain. I've run tests on AC frequency response and the 12AX7 gives a flatter response curve. This is useful when doing audio and video P-P measurements, but then that's why I have a scope now.
I'll have to try that tube swap. 12AU7's are getting tough to find. I keep a working VTVM because I restore old Hallicrafters SW sets. I have an HP 100mhz scope for other needs. Thanks for the tip.
While the 12AX7 has a higher amplification factor, the 12AU7 has twice the transconductance and 10x cathode current for same grid bias and plate-cathode voltage. This makes the 12AX7 unsuitable for the Heathkit VTVM current mirror circuit. It like!y would not drive the meter to FS deflection.
Are you a fan of Mr carlson’s Lab channel? Great vid btw
That replacement probe looks dangerous. if you are testing 300vdc what is on the end of the AC probe?
One difference between the IM-18 and the IM-11 is that the IM-11 has a single input power transformer of 115VAC but the IM-18 came with a dual input on the transformer so the builder could choose between 115VAC or 230 VAC.
Where do you find the Corniel Dubilier WBR16-150A? I only find quantities in the hundreds.?
I did not buy it from a mainstream electronics supplier.....I think I bought it from some place via Amazon......
Mouser seems to have them in stock, and I don't think that they have a minimum order......
Buy-Capacitor.com also shows stock......
Any capacitor with adequate voltage and capacitance ratings will do. I have a Knight VTVM almost identical to the Heathkit save the probes, and just used a 22uF/200v cap I had in my parts bin. It was a radial leaded cap, so it looks different, but still fit.
3-Line cords are a NO-NO! Daystrom was the original designer. I've seen others use a 1000uF & 27 Ohm resistor.
At 1:03:05, there might be an un-balance in the 12AU7. All-in-All, good job!
The three conductor line input is more dangerous than just a two lead power cord. The meter has line isolation via the power input power transformer. Why would you then tie the chassis ground to one side if the line? Three conductor line cords were made mainly for appliances .
Hi - nice clear video.
However at around 56:22 you calibrate the 1.5V to the red dot.
This is incorrect, a new "C" or "D" cell put out 1.6V not 1.5V.
That is why the red dot is off the scale.
You are using 1.5V - so set the calibration to 1.5V.
This should fix the 5V problem.
Mick M.
Mick M, good point......I will revisit this with my meter and see how much it helps. As it is, it still meets Heathkit calibration specifications, but I will improve it if I can by this means.
YO Mick! You are talking about 100 millivolts difference. The standard voltage is rated at 1.5 not 1.6. Using 1.6 as a standard calibration voltage will surely put you meter out of calibration quickly. That ok though, as you will never even notice it. True calibration should be made at the top 2/3rds of the meter scale for any true accuracy, not to peak and. It below 1/2 scale. After all is said get over yourself . This meter is not lab grade. Get over it!
Bought a brand new 260 for $99. Never had a battery installed and in the original box.
I wish I knew more about Electric Power. I want to build my own Generator.
Where can I buy one?
Looks a lot like my IM-10 , don't know all the differences in these two models...I miss Heathkit !
Heathkit used this same classic VTVM circuit in several models over many years, only changing the styling to 'freshen' the appearance. I have read that some of Heathkit's competitors also used essentially the same circuit in their own VTVMs.
Re: Adjusting, There is a seperate procedure for A.C. calibration. Assembly manual page 24 A.C Calibrate with line cord adapter (2 Wire outlet) Page 25 A.C. Calibrate without an adapter (3 wire outlet). Perhaps using an isolation transformer would necessitate the 2 wire non grounded procedure.
Apologies, I thought you were powering from the isolation. I could not edit out that last comment.
Apologies, I thought you were powering from the isolation. I could not edit out that last comment.
My mistake , was looking at the capacitor, sorry.
If you are worried about the 47 ohm 1/2 watt, take two 100 ohm half watts and wire in parallel.
That really depends on the accuracy you want. It's good enough though.
On DC calibration, the instructions have you use the internal C battery as a voltage reference. But you just eliminated the battery! You're just lucky that your circuit produced a voltage very close to a fresh carbon-zinc cell, not the 1.4V that you expected. If you build a battery eliminator, use a fresh battery externally, or some other trusted voltage reference for calibration.
Randy Shoquist, it was not luck, it was by design, and verified by measuring the eliminator circuit's output (being essentially 1.5V) prior to doing the calibration.
When en you zero the meter on low ohms . The light dims. The 6volt xformer is not really strong enough.
Ira Lee Martin, I just tried it again and the light did not dim. And it should not, because the current pulled from the battery eliminator circuit by the Ohms meter circuit is a tiny amount; the quiescent current pulled by the battery eliminator itself is much more than the Ohms function draws. Or are you saying that the light dims on YOUR meter when you do this?
A few things, please take this constructively.
First, the voltage drop (insertion loss) on a silicon diode is relative to current. The correct way to design this circuit is to, before anything else, measure to current draw on the battery with the ohm meter working. It measures at less than 0.001 mA. This stands to reason because a battery drawing 120 mA wouldn't last very long, even with today's batteries. I used a 1.5V low current regulator, about 90 cents (Mouser part# 628-S-817B15AY-Z2-U). This is an LDO, TO92 package low current regulator. 120 mA is way too much for the transformer to handle and eventually it will burn up.
I ran a 1N4007 diode into a 100uF at 25V capacitor and put a 1uF @ 10V cap on the output of the regulator. I checked the voltage of my DC, it was 8.25VDC. My bulb was burnt so I replaced it with a red LED. Incidentally, this is only an on indicator and not designed to light the meter. I tapped the 8.25VDC lead and put 470 ohm resistor in series with it. Play with your own LED and resistors if you decide to go this route. My final LED current was ~13 mA. The total current on the transformer from the 1.5VDC and the LED was under 20 mA.. There are no warm or hot components.
The problem with using two silicon diodes is that they do not regulate the ohm drive voltage so you will get erroneous readings. If you must go this route use a much higher resistance. I don't know where 47 ohms came from but it's entirely wrong. Remember the circuit only draws about .0009 mA.
I changed the 16uF cap too. I used what I had in my box a 47uF @250V. You don't have to use the same cap, in fact you get better regulation with higher capacitance but don't overdo it. Just as long as it's equal or better than the one it's replacing.
When I was done and calibrated the meter it was quite satisfactory and lots of fun to use. I worked with these meters as a kid in a TV/radio repair shop in the late 60's. The standard at the time was the RCA and I think the Heathkit was likely modeled after it. We did a lot of trouble shooting with those meters. In my Navy days I trouble shot radar systems and the first military computers. They did the job along with CRT Tek scopes. Today I use a Keysight 34465A that goes down to picoamps, quite a difference!
mosfet500, I do take your comment constructively. However, my "design", such as it is, works just fine and the meter performs as specified and tested. The transformer is a bit more loaded than it would be in the original design, but not enough to cause a problem for it.
You mention that the Ohms range will not be stable when using my battery eliminator, and yet it works just fine, so instability is not apparent, and it is well within Heathkit's published accuracy. Also, this diode dropping technique is widely used in all sorts of products, not just my own "design", and is in fact a commonly endorsed circuit used by many people who restore VTVMs. You are correct that the voltage drop is on a bit of a curve, but in this circuit that is not important; the Ohms range needs to be adjusted regularly anyway when using the battery, and it is no worse when using my circuit. True, a more tightly regulated circuit might not require adjustments as often, or as much, but again, I was not trying to improve the meter's nominal specifications, and I have not made them any worse.
You have also mentioned that you used a 1uF capacitor on the output of your voltage regulator. What was that value based on? I know it is a common "guesswork" value, but most 3-terminal regulators actually need only a smaller value capacitor there.
@@youtuuba The heater current for the 12AU7A is 300ma (parallel). The heater current for the 6AL5 is also 300ma. That means you're taxing the transformer 20% over the circuits design criteria ((720/600) * 100)). The problem is that this is a very low current circuit, in fact, batteries last years in these meters. I only changed out mine because batteries leak and I wanted to avoid that. Why put a circuit in to fix something when that circuit stresses components, especially in a closed , unvented cabinet with hot tubes. I turned on the meter with the cabinet closed and measured the temperature at 49C (120F). What is the value of adding 20% more load to that relatively small xformer?
A 1N4007 diode exhibits a Vf of of ~575mV at the working circuit of 1mA, at 120 mA the Vf is ~800 mV. You can use it and so can other people but it's just not a good solution. The problem is that, while your voltage is slightly higher than a nominal C cell you have to run high current to get it there. Let's say we ran the diodes at 0.001 mA and 1.15V. This is below the design voltage for the meter so then you run into adjustment problems because your basically working with what would be a dead battery. So the diodes are really a poor choice especially when you can run a low current LDO for 90 cents.
Try using a 2k resistor, this will give you ~ 650mV (~1.3V total) drop per diode and around a 3mA load which should be enough overhead. The problem is you never tested the most important factor - the load on the battery. It's poor practice to run a circuit at 120 times it's required load. Again, sure it might work but for how long? Leave it running on the bench for a couple of years and see what happens.
Removing the Bulb for an LED reduces the xformer current by about another 180 mA, so in my design I've reduced the total circuit load by over 150 mA where you have increased it over 120 mA. My circuit is also much more accurate. Sure yours might work fine but you would have been better off just changing the battery. Because this was manufactured in the 60's doesn't mean we need to limit ourselves to that technology when simple solutions make the overall design better.
Not trying to give you a hard time, it's just electronic engineering, you did name your video "Hacking and Overhauling..."
@@mosfet500 , you are making an argument where none is warranted. You say that your argument is 'just electronics engineering'.....but I am an electronics engineer with a lot of experience, for over 40 years. One thing I have learned is when certain criteria just don't matter in a given application. You cite the load posed by the tubes, and suggest that my circuit pushes the components past their design limits. ..do you know what those limits are? Heathkit did not publish them and the schematic and parts list don't indicate the current rating of the transformer (which is the only part that might be stressed). Absent specifications, I used solid empirical methods to determine if the transformer could handle the extra load without problems, and it could. I tested the meter extensively over many hours, and the transformer did not get warm or show any signs of stress. My circuit does what it is supposed to do, and does it without problems...that is a big part of engineering right there. Could I have done it some other way? Of course. Was there a need to do so? None whatsoever.
@@youtuuba You have a circuit drawing 120 to 140 mA to run a less than 1 mA load.
You said someone else on YT did the same thing, then you both have a resistor exceeding its wattage limit, how is that engineering?
I measured 8.25V DC (empirical) into the 47 ohm resistor. It proves out: (6.3ACV (filament) * 1.4) -0.7 = 8.2 VDC. Dropping 1.6V across the diodes = 6.65V; I = 6.65/47 = .1414 A ; I^2R = .94 watts. Think it's wrong? Simulate it in SPICE, you'll get the same answer. You used a 1/2W resistor, didn't you? Looks like 1/2W to me. And you're running the xformer 20% over the original design when you don't have to.
Run it on your bench for a year and tell how things work out.
I'm trying to help people not make the same mistakes you did.
@@mosfet500 , I said that many others who are on tube circuit forums, vintage Heathkit forums, vintage radio forums have been successfully using the same circuit a great many times. I don't think I said it was on TH-cam.
But I am getting tired if this. You are asserting many more things than I want to take the time to address. But no matter how many arguments you make to the contrary, the fact is that this circuit works just fine, as so many other people have learned. No components are stressed in the way that you seem intent on proving. Which means that there is an error in your data, calculations, or reasoning. Think about it...if all you say is true, then it would not work as well as it does. Nothing in the new circuit is getting more than VERY slightly warm.....by your calculations, they would have to be a lot warmer, even somewhat hot. The transformer is just fine with the extra load, and that is a fact. The resistor could dissipate a lot more than it is doing (resistors running at their rated dissipation are a lot hotter than what is in my circuit. So, please, give it a rest. I don't dispute that another circuit could be better, just that this circuit works well enough and does not cause any real problems.
I wrote an article in the 1980s for Electronic Musician magazine on the basics of using op-amps to make simple instrumentation amplifiers that had application as preamps for balanced microphones. I gave classic textbook formulas for calculating the component values, and even provided the editor with facsimiles of commercial microphone preamps that used the same circuit and whose component values validated the formulas I provided.
One reader wrote to the editor saying that the circuit I provided, and the formulas, would result in a non-functional amplifier, or one with very poor performance. I defended the design, cited the commercial products, and provided the editor with the commercial circuit diagrams. I cited my many years of experience in designing and building such amps for radio stations and recording studios. The guy responded by sending in pages of calculations which he said proved that my architecture and math was wrong. The editor forwarded to him copies of textbook design notes, had other writers build and prove the accuracy of what I had in my article. The guy kept telling us that we were all wrong. None of us had the energy to refute his calculations and reasoning line by line.
That is the way this exchange feels to me.
nice mod.
So it looked like you used 470 ohm instead of 47 ohm 1/2 watt?
judges69, it is color banded Yellow Violet Black, or 47 and 0 zeros following, or 47 Ohms.
That pilot light is useless, it's mainly to let you know the power was applied. The bulb is blinding. It does a terrible job illuminating the scale.
I like the same, fun to do, eliminating the battery, but why is that the Heath kit engineers and most of other brands of VTVM's used battery for their VTVM's design? a single alkaline battery will go far, life time for this device, so, no need to touch its original state of the art design since they are part of our electronic history, good or bad, that was my idea, by the way, very nice job and perfect video with outstanding explanation.
Batteries were cheaper in manufacturing. They also carried over circuitry from the VOM meters that had only a battery for a power source on the Ohms scale.
The eliminator is a clever idea , however much overkill. You are also decreasing the values of an antique. The time and material used in constructing the eliminator , plus labor and reliability,make the idea ridiculous.
@@erin19030 - Do you really think your version of how to enjoy a hobby is the only way? Who cares whether the guy spent a zillion hours and a billion dollars on his hobby?
Cosimo Kramarawicz Anyone messing with these doesn’t really care about their value as an antique. A working one is worth maybe $30, anyone paying more than that must just really want one badly. I see a ton of these on FB a being sold off for $10-15 after initially asking $70-80 because they have rather limited utility today. You have one on your bench because you like to fool with old meters, not because of its performance.
@@erin19030 Yeah, but, batteries when forgot eventually shit themselves all over the inside of your instrument, even alkaline ones. I think there's enough of these in museums already.
building a circuit using the lm317 to92 case full wave bridge it should be pure and rock bound regulation
make sure the plastic is static free that will throw it off
The 817B15AY is a better option, it's a 1.5 volt LDO low current TO92 part at ~90 cents from Mouser.
@@mosfet500 Thank you
@@mosfet500 That 817B15AY is a 50mA reg (if I found the one you mean). On the low ohms scale shorting the probes pulls ~150mA.
@@bob_mllr I'm not sure what you're asking but it sounds like you have it hooked up wrong. The regulator should only supply regulated power (1.5V) to the circuit, the load on the circuit determines the current draw. If you're getting 150ma when you short the leads you're likely shorting the regulator, check your circuit. The regulator is from Seiko, check the data sheet to see if you have the pin out right.
I bought a probe set on eBay for 18.00 + 3.75 shipping it's for my heath kits V7A ,his price was a lot cheaper,and the set look amazing if you want I will give you the seller name ,both people make nice probe sets,me I am on a budget,so I will around but I want a good set of probes too.,I understand they make a tube heath kit IN -18 one with tubes and one with some sort of a solid state device that plugs into the sockets ,I forget the name of the solid state version.is called ,do,you no about this.
Ron Thompson, I really wanted to understand whatever point you were trying to make, but kept getting lost with the very unclear writing and punctuation problems. If you care to revise what you wrote, I will be happy to read it.
For us hobbyist it hard to find a Heath kit vtvm in decent shape ,you should see how much people want to charge for some really bad vtvm ,they think old it must be a gold mine then you will have to restore them .
i just bought a old one to use to check volts and oems on a motor cycle charge system..
Jake Lang, a VTVM seems like a poor choice for what you describe. High impedance meters can cause unexpected and confusing results if used improperly. A basic VOM would probably suit your needs better. Also, BTW, the word is Ohms.
@@youtuuba its a old heath kit but i think the tubes are blown..im not even getting the meter to move when i plug it in..any tips? its a nice looking old machine..i just what to use it for any need really
@@youtuuba i took the old battery out and cleaned up the contacts..put new in
@@youtuuba why is it a poor choice" to use these machines for what there purpis is?
the old jack has better protection than you new one for high volts look at the bigger black seperation from tip to grd
You can use a stereo 1/4" plug and just leave the ring connection open. But the best plan is, don't fool with the probe plug while connected to the DUT.
The two probe test lead system is the best. The combo probes were crap and always failed.
Pardon my hacking. I did enjoy the video, but a lot of smoke was blown about.
I built this and on x1 it pulls 150ma with probes shorted. The supply would only push about 50ma. Therefor none of the Rx1 reading were close, about 3/4 of what they should be. 150ma x1, 15ma x10, 1.5 x 100........ you get the picture.
I DON'T get the picture, other than you built "this thing" and for some reason it did not work properly. Mine worked as described in the manual, and in all resistance tests I did. You mention "pushing" amps, not a very technically valid way of describing electronics. So I cannot tell if you are experienced or knowledgeable. But many others have done this and had good results, and I have read in forums where others have done virtually the same thing with good results. So the only picture I get is that you were not successful, but I don't know why. At least it is simple, easy, inexpensive, and reversible.
youtuuba only thing I did different was use a 100uf cap as described in another video from an old gent who said he worked at Heathkit and that was the values they used. Also my Heathkit is the older V7. I used a 27ohm resistor over the 47 you used. What I was saying is that under the load of the probes shorted with my bench power supply to test and an amp meter in series it was drawing 150ma at 1.5v(10ohms) in range x1. The supply I made was identical in circuit construction other than the values I mentioned. It did not have enough current on tap to run the range x1 properly and maintain 1.5v, it got better as the range switch went higher because of resistance increase of x10 exponentially with current lowering at the same. The AC voltage wasn’t dragged down by the supply when I started testing either. Thought I might get a helpful answer, sorry if wasn’t specific enough. I’ve seen some that you can buy that have a LM317 regulator in the circuit, don’t think that would be necessary as the 6v AC is pretty constant for this. I’ll try it with your value of components and see if works better. I realize after seeing your reply I made the comment to the wrong video, I watched quite a few for this circuit. Should have asked the guy who’s circuit I used. Sorry bout that. Here’s a link to his video, read some comments and one guy had the same issue as I did with his V7. He used an LM317 in his next try. Obviously the components value might be the issue. th-cam.com/video/IlaGhx2rqK8/w-d-xo.html
@@SIXSTRING63 , try using the 47 Ohm resistor, as you are loading the low power transformer secondary a lot more with the resistor you used. Also, there might be some different internal resistors in your different model meter, which might more heavily load the transformer.
Also, you said that you hoped to get a useful answer, yet you used less than precise language and while you claimed to be doing the same thing as in my video, you failed to mention the component value changes and the different model of meter....so in fact you did not do what you initially claimed to be doing. You are more likely to get good information back if you provide good information.
youtuuba Thanks for getting back to me. If you read completely I did mention I commented initially to your video instead of the original video where I got the values from. I did apologize for that. Yes, I believe you’re right on the loading part. His video was for later models also. Like I said, a reply over at his channel one person had the same issue with the V7 as I did. I looked at the schematic for the v7 compared to the IM18, really only difference I could find was the 7 has a 10k ohms adjust pot where the 18 is 15k. Maybe the meter internal resistance and FS amperage are different too. Wouldn’t think so with the same value resistors in the ohm range voltage divider network.
@@youtuuba Thanks for the advice. Once again, sincerest apology for commenting that it didn't work on your video, my mistake on that one. I did some experimenting and found that none of the values you listed or the other YT'ber video where I got my component values from worked well. I finally tried a 3300uf cap with the 27ohm dropping resistor to maintain the voltage on low resistance measurements and to not drag down my filament voltage too much. Mine only is running around 5.750v with just the tubes running. The schematic says between 5-6v on this tap so I guess it's within the design parameters. Drawing the most current in the Rx1 ranges from a 1ohm load to about 10 it pulled the voltage down from 1.6 to around 1.45v but seemed to be pretty close. I guess I'm trying to be a bit too fine on this old meter accuracy wise. I think I will just build it with what worked on the breadboard and call it a day. For a $10 hamfest find it works well for it's age.
Quiero traducir al español
I'm sorry but those probes are very dangerous. There is a disclaimer that states voltage is present on both probes when testing. If you are doing B+ testing that is pretty dangerous. Also the meter is rated to 1500V. Are the probe wires rated to that level or just to 600V? Also look at the 1/4" plug. See how short the insulator is between tip and sleeve? Not a 1500V insulator. If you only use this for low voltage (50v or less) testing then you should be fine if you keep the unused probe in a safe place.
mike94560, don't be sorry. However, what you are talking about has nothing to do with the subject of the video. These are limitations and concerns that are typical for meters of this type and vintage, and not just Heathkit....other manufacturers in those days did the same, or similar, things with their products.
Hey, if something MAY be "still OK," better off doing NOTHING... RIGHT? WRONG! I can't watch something so stupid as a video with that mentality, no matter how "brilliant" the person is who THINKS they are doing a good job.
You have a decent scope. Why do you need a VTVM when a VOM will suffice?
A D cell battery can put out 10 amps, without the ripple of an eliminator. I like the battery idea, but you need to use a good quality battery.
why not use an led instead of the bulb,that should be less stress on the transfo for running the bat eliminater in the low ohms ranges+ less heat.
Even with the incandescent bulb removed, the rest of the circuit in low Ohms puts a lot of load on the transformer. But that is OK, as it is specified and verified to be OK with that load.
And yes, somebody could replace the bulb with an LED, but why bother, and probably most VTVM owners wish to modify them no more than necessary.
@@youtuuba just thought it would be more reliable,i have a v7au i am working on,was going to use an lm388 vreg but your reg looks better,73 m3vuv.