HEATHKIT VTVM , BATTERY ELIMINATOR CIRCUIT FOR HEATHKIT VTVM
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- เผยแพร่เมื่อ 7 ก.ย. 2024
- If you are working on a VTVM of any type remember it is a 120 volt or maybe 220 volt powered instrument and you can get a shock . You could also be injured by the voltages in a VTVM meter SO be sure to UNPLUG THE VTVM before working on it ! This is a HEATHKIT IM-13 VTVM Bench model VTVM made in 1963.
A very good instrument for an electronic workbench it appears to be the factory built model because of the very good assembly and the fact there is no heathkit sticker on it . A VTVM or
vacuum tube voltmeter has a very high impedance input the Heathkit VTVM's have an 11 megohm input so they do not load down the circuit . Every service bench and engineering workbench at Heathkit had at least one VTVM and when aligning Heathkit equipment it is best to use a Heathkit VTVM . I recently aligned the phase locked loops for the HFO oscillators on a Heathkit SS9000
tranceiver and it did not work right . I realized I was using a plain old VOM meter . I did the alignment over again using a Heathkit VTVM and the SS9000 works great . testing the VOM and VTVM both on the same circuit the VTVM was giving a different reading .
The diodes I used to make the battery eliminator circuit actually measured .7 volts drop across each one making the voltage of the battery eliminator circuit 1.4 volts . So my statement that the diodes have a .6 volt voltage drop is an error these diodes actually have the .7 volt drop . One last thing the parts for the battery eliminator are very non critical the capacitor need not be 100UF it can be up to 500 UF and any voltage over 20 volts . The resistor can be any value up to 39 ohms . I did a couple of these using 39 ohm 1 watt resistors and they work fine . The diodes I used on this one were common 1 amp black plastic diodes from a hamfest .
Re-alignment was then done for OHMS due to the voltage difference between the battery and the battery replacement circuit.
73 Bob
Hi All - I’ve built the battery eliminator and it works great! One small tip - the 27 ohm resistor only drops about 2 volts, so it only dissipates about 0.15 watts. I used a half watt resistor, which works fine.
Hello, than you very much for the video, i added the battery eliminating circuit to my V-7A and it works great. Took me 30 minutes.
I just started restoring one of these that belonged to my granddad. Battery got left in for about 25 years, so there’s some damage to sort out! That battery eliminator circuit is a keeper. Thx, K8TIY.
Hi Bob, Thanks for another enjoyable and informative home grown Heathkit video. I have Heathkit V7 VTVM, maybe circa 1959 and did the battery eliminator modification just like yours. Using the two 1N4001-7 diodes as the regulator/constant voltage source - - - the Rx1 scale could not be adjusted to Zero Ohms with probes shorted together. Experimenting revealed that the 1.55 volt copper top cell was needed for Zero Ohms. I replaced the two diodes with LM-317 linear VR set to approx 1.6 volts and the old V7 works on Rx1 and all other scales. As they say, YMMV- and mine did. FYI, 73, Happy Trails. KR7W.
Rich , Looks like you revealed a problem there . I have done several of these with no problems and We had this circuit in many VTVM'S in the plant I wonder why yours did not work ? You came up with a good solution ! 73 Bob
I had the exact same issue. Another poster commented on this thread that if built this way it will work, not on my V7a it didn’t as it didn’t yours. Same issue, not enough current to drive the meter in Rx1 setting. I breadboarded mine and found a bigger reservoir cap did the trick. I will be using the LM317 design eliminators on my other VTVM’s.
Just modified my IM-13. Works great. Thanks!
This is one of the best circuits I have used Bob Thanks for sharing. Both my IM25 and I am in the process of completely building a V7 from Scratch it was in a house fire and is realy toasted main board was badly burned I have got it ready to make the new board this circuit will be added to that one also And my RCA WV-77E has it installed what a fun project Keep up the videos Watch them all
Thanks Robert, I am working on the meter I built in high school and found a leaked battery, Once I clean up the small mess I will build this and never worry again. Thanks again.
note that you don't even need to filter the d.c. since the meter will respond to the AVERAGE value of the pulsating 1/2 rectified d.c.
You can select components to yield about 1.5 volts average value with decently low source impedance. Neither that approach nor this circuit regulates well on X1 range when measuring low resistance like a speaker voice coil or a light bulb filament. Very good performance for high resistance DUTs like a 1k2 resistor and the like.
Awesome 👍,thank you for the diagram. I'm going to use it on mine. Thanks 👍
Hello Robert. This weekend I built your circuit for 2 of my VTVMs, Heathkit IM-28 and an RCA WV-77E. It works great, I get 1.45 Volts out of the circuit. I checked all Ohms scales on both VTVMs using an Ohmite 1% decade box and all readings are spot on. On your schematic the diodes are not marked but you quickly say what they are and for those that didn't catch it, they are "1N4007" diodes. Thank You for posting this video.
You could use any diode in the 1N4xxx series for this battery eliminator circuit. The 1N4007 is rated for 1000V, but since this circuit never gets above about 6-7 Volts, even the lowly 1N4001, rated for 50V, is more than adequate for the application. I used 1N4004 (400V) diodes in the ones I built, just because that is what I had in my parts bin. The whole 1N4xxx series is good for 1A constant and 30A non-repetitive, again way more than enough for this battery eliminator.
@@youtuuba Good to know! Thanks. GB :)
Good job on that VTVM sir
Absolutely wonderful video - and you are fun to listen to.
Thank you Mark I want to help other Hams like I was helped by Elmers I knew thank you for your encouraging comments 73 Bob
Excellent video. I have an IM-13 as well as a couple of V series. I will make these battery eliminators. THANK YOU!
I do this when I restore VTVMs. But my circuit is a diode, electrolytic cap, an LM317 on a small heatsink and a couple of .1 caps on the input and output of the 317. Same plan to connect to the ungrounded side of the filament. Same circuit works for 1 or 2 cell meters as you can adjust from 1.2v to whatever the filament winding can give you, 8v maybe. for a one cell I set it to 1.45 and for a 2 cell I set it to 2.9 volts. But the best thing is there is almost no extra load, so no big power burning resistors.
Good Idea I like it 73 Heathkits forever ! Bob
Joseph Cote I think I’ll have to try your circuit. This didn’t work well with my old V7a. In the Rx1 range it didn’t have enough current to drive the voltage divider properly on low resistance readings. Drained the voltage to under a volt with probes shorted. Meter draws 150ma in Rx1 with probes shorted and draws more current than this circuit will supply to give you accurate readings. Works fine in x100 and up, less current needed.
@@SIXSTRING63 Just use a LM317 in the TO-220 package, more than enough drive current that way.
I ended up just changing out the cap to a 3300uf. That kept up with the current demand and only dropped to about 1.35 v under load in the Rx1 scale. I will rebuild it though with the LM317 down the road.
Thank you for schematic. 😀
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
Hello Mr. Sumption, first time view to your channel, this video is very interesting to me. I am the owner of several Heathkit test equipment. The Heathkit Model IM5284 VOM, the IM2260 digital meter, and the Heathkit IO4335 oscilloscope.
I really enjoy watching video on Heatkit products, they were great in the day...
Nice, going to have to do that to my Heathkit vtvm
That layout is so much cleaner versus my V6 vtvm. :)
Nice job! You didn't mention about the Cadmium oxide on the sheet metal screws. (nasty stuff) Tin whiskers on the cal pots can be an issue too. A very good instrument for 1963 design. The low current, large scale, d'Arsonval jeweled meter movement is the key to its high accuracy. I've got an IM-18 in very good condition - really nice legacy instrument
👍😁 Thank You ❤
I independently developed this same battery eliminator circuit when I hacked my own Heathkit VTVM, the only difference being that I arrived at a value of 47 Ohms for the dropping resistor, instead of the 27 Ohms suggested in this video. My meter works fine with the battery eliminator using the 47 Ohm value, the Ohms ranges all work with the full range of my resistance decade box.
That did not stop an overzealous viewer from repeatedly and persistently claiming that the battery eliminator design I showed in my TH-cam video of the hack would not work properly, and/or would result in the VTVM not working properly in all Ohms ranges (yet it DOES), or somehow using such a battery eliminator design would damage other parts of the VTVM circuit, e.g. the power transformer. I feel vindicated what I see others happy and successfully using the same circuit.
Nice project! I have a Knight KG-625, that's a horizontal. I had to do some work on it to make it 100 percent...may have to do the battery replacement ckt!! Thanks
I use deoxit 5 contact cleaner,nice repair
I'm trying to calibrate a Nakamichi RX-202 cassette deck for bias and for azimuth. The service manual says to adjust to 350mv and/or -.8db on a VTVM. I understand 350mv but never got familiarized with the db scale.
I have a heathkit AV-2 coming in the mail that looks new. This is an audio meter that measures only AC and in very small amounts as it has a 0.1v scale setting all the way up to 300v. Db seems to be a very much used reading so if you ever do a video on that subject or have already done so I would be very interested in the tutorial.
I will subscribe and look,thanks for the information and on self cleaning switch and the schematic of the C sized battery. So simple 🙂
im trying to learn to use the one i just bought
I have quite few VTVM's but no IM-13 yet. I've got some boards ordered for the battery replacement. I went with surface mount parts so the board is only 1" square. It'll be interesting to see how the 2W SMD resistor does. I have a few other ps boards that I can use but they have an LM317 and more parts. I figure if Heathkit developed and used the circuit in your video that's good enough.
Mike Yes We all had Heathkit VTVM's on our workbench when i was in the service department and as far as I know all of them had this same simple battery replacement circuit . 73 Bob
They have lm317 to92 style case. Thinking of using it.
Hi Bob. I have a Heath Kit V4. The schematic shows a 6 volt battery pack bur the meter only has a single battery holder. I m seriously considering a battery eliminator. Thanks for your videos.
Brad
Hi Bob,
I’m retired technician from the Bell System. I have a Heathkit IM-5228 VTVM that I built in the 1970’s. I recently decided to spruce it up. I used black anodized hardware to replace the oxidized ones. I also checked and cleaned all the contacts and replaced the electrolytic capacitor.
I’m thinking about a battery eliminator and found your video. I like the simple design and especially the fact that the one you discus was designed by Heathkit.
How do you feel about the LM-317 based eliminators? With the 5228 eliminating the incandescent bulb from the filament circuit it should be able to support such a device? I’d like to hear your take on it.
Regards
Tom Heckhaus
Very nice project, Sir! I restored one myself and found it to be quite accurate for the rest of my Heathkit restorations. One problem I'm finding out is that the pots used to calibrate the unit on this and my IT-28 aren't available as NOS or pulled stock. What can we use now in place of them that will fit? Quite the problem to work out.
I'm hoping to get mine up and running soon and I'm going to use this battery eliminator. Thanks for the tip. I picked up two IM-28's, one with manual and probes. The 9.1 Ohm 2W resistor on the best unit is out of spec at 9.68 Ohms, even for 5%. The other is right on the line. The parts list calls for a precision resistor and both the ones I have are 5% (white-brown-gold-gold). The short glimpse I got of your IM-13 also appears to be 5% (unless the color on my computer is off). I haven't found anything during research to contradict the manual. Do you know what the deal is with these?
At 4:38 you show the diodes facing towards the center post, but at 5:30 they are pointing away.
Some beginner won't understand.
In either case the 2 series diodes banded end is connected to ground and it will work fine . 73 Bob
Good morning mr. Robert! How is it going? very good video, thanks for your input! I was doing some tests with your design of the battery eliminator for vtvm! And change 2 elements that were the 100uF capacitor for a 3300uF one, and the 27 ohm resistor for a 10 ohm one. Which gave me more stability at the 1.5v output. I don't know if you, for your part, do some tests and help me know if the change is well done. I hope for your reply very soon ...
Leonel Good Job what you have done should work fine.... all the best for 2021 Bob
@@robertsumption1243 thank you very much mr. Robert! I mounted it today and in real tests it gave me exact 1.6v! I don't know whether to lower the capacitor and to 2200 so that it is closer to 1.5v! or increase the resistance to 22uf!
Leonel Test it and as long as it works correctly 1.6 volts is fine 73 Bob
Did you take the spring out to clean it,I did but putting back is a challege,if anyone has any secrets to puting it back,please let me no .
Bob, the internal layout seems far less crowded than the V7A types. Your unit looks go be in great shape. But wondering how the DC and resistance measurements are? They within the 3-5% accuracy?
Yes the IM13 is quite accurate
Is there any concern about ripple in the rectified DC possibly impairing the accuracy of resistance measurements?
This was developed in the Heathkit factory by one of the engineering staff and was completely tested to see that the VTVM'S worked properly to specs. I do not know who that was that designed it . I do know that many of the VTVM'S were modified this way in the Heathkit factory . 73 Heathkits forever ! Bob
I just got a Heath kit meter like your upright one.,is that a c battery that goes in them ? I would appreciate your help with any of my questions you can answer,mine came with out any of the test leads ,I ordered test leads for the one on.the right and left sides ,but the 1/4 probe test lead or probe ,is that something I can.make ,anyone,or is there someone.who still sells them ,the person I bought mins.from didn't have the center test lead or probe so they wire a red wire through the whole ,I no that not right ,I ordered a new female 1/4 plug for it and and a new mono male plug 1/4 for it ,just in case I need it ,if you or any of your fans that have any info I would be grateful if seems to be a nice meter other wise ,I will order new caps to replace the was lapped caps that are in there
I have the IM-28 and it still needs work the readings are off not acurate
I have one for more than 50yrs but it is highly unstable... I don't recommended it.
Why would u do this to a vtvm? By doing that u alter the ohms per volt sensitivity of the meter. The purpose of a vtvm is just that. The battery lasts for years, The power for the ohms section has to be isolated and float. Theres no gain to it your just degrading the meters specs. Why do u think Heath kit or any other manufacturer didn't do that? You might as well get a solid state meter and discard your vtvm.
Nice video I love my Heath kit IM 5228. Keep up the good work. Billy K9ZL