Heathkit V-7 VTVM Repair

Repair of an old Heathkit V-7 Vacuum Tube Volt Meter, 1957 vintage. This has tubes and everything for the vintage test equipment lover.

[@tomaskey6844]

I just bought one and the shipping was more expensive than the unit. I didn’t know it was a vacuum tube meter so now I’m even more excited.

[@AERVBlog]

Hope you enjoy it! A good VTVM is very useful. Some things just work better with an analog meter.

[@joramkalfa4038]

Hey AERV, I know this video is quite old. I'm lucky to have found this video. I just got one of these Daystrom's and had to open it right away LOL. I'm wondering where you found your schematic? It's hard to determine the values of some of the components. Wax caps etc. Thanks for a fun video.

[@AERVBlog]

Contact me at [e-mail] please.

[@judges69]

Great video, I have the IM-10

[@AERVBlog]

judges69 thank you. I used to have one of those. I was a technician for Heathkit on the mid 70s so I have used and built a lot of Heathkit equipment.

[@emylrmm]

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

[@AERVBlog]

Thank you. I think I knew that once way back when radios doubled as night lights.

[@erin19030]

Heathkit made affordable quality test equipment for the novice and service techs.

[@AERVBlog]

Yes they did. If you were willing to put in a little, or in some cases a lot, of work you could have the better stuff for less. That was true for ham radio too. And don't forget the color TVs.

[@6A8G]

Just a quick note about the battery eliminator, it's not so much a question of buying a new battery every so often, it's more the chance of leaving a flat battery in service which subsequently leaks & spreads corrosive goo onto adjacent parts. Not a pretty sight.

[@AERVBlog]

6A8G oh yeah. Many hours spent cleaning up that mess. I have even had to electroplate some pieces from time to time to make something work.

[@bucyruserie1211]

I just found one of these units 4-23-19, along with a Sencore Vacuum tube tester (they both worked) at my town's recycling center. And just for the record, my VTVM still had the 1.5 volt "C" cell battery inside of it (I guess it was used to keep bias on the tube?) The VTVM was made from 57-61, the battery was an Ever ready with the cat on it, i'm guessing it was from the late 70's, It didn't leak, and still held 1.495 volts DC charge on it! Pretty neat I thought..

[@EJP286CRSKW]

Bucyrus Erie12 The battery is only used for ohms. Most VTVm owners would also have had a DVM by the mid to late 1970s, and you would always use that for IBM's in preference to any VOM or VTVM. So many will be found sans battery, or alternately with the battery intact. It draws very little current. I still have a VOM from the 1970s with the original battery, still working.

[@genesisramos14]

Did my stop running the D.C- and D.C+ scale, would you have a clue what it can be?

[@AERVBlog]

Take a look at the DC calibration pot and the common wiper on the number 2 deck. If everything else is working then the tubes are good. Let me know.

[@nor4277]

Sir have you ever shipped at Ali express,you can get a couple hundred of the blue small high voltage ceramic caps for a couple of dollars they work great or any other cap you need .just a thought .I have the heath kit v7a and a I'M - 11 .I just started going through and getting parts,etc ,I love vintage equipment ,

[@AERVBlog]

I have gotten some stuff from Ali Express in the past. I have never had any problems with them except for the long turn around time. Good luck with the Heathkit meters. Thanks for watching.

[@tomheckhaus7617]

Hello, This is an old post and I came across it trying to repair an old IM-18 VTVM from your video it looks like the schematic was identical using the 12AU7 and 6AL5 tubes. MY problem is no meter deflection when powering up. AC, DC- and DC+ scales are all dead. But ohms works, but is very inaccurate. I've changed the tubes and upgraded the old wax and electrolytic caps. Any ideas? Thanks.. Watching the video, I usually cut the power leads to get that frame out of the way. The ground is held in by a screw. Reassemble using wire -nuts.

[@AERVBlog]

Check the disc capacitors too. They are most likely bad.

[@tinagladu3744]

ENJOY YOUR VIDEO,JUST WONDERING IF YOU DO VINTAGE AMPS

[@AERVBlog]

I can. Please contact me at [e-mail]

[@nor4277]

I have one theses heathkits can anyone help me ,I need to find or make a replacement for the center probe the one with the 1/4 mono jack in the middle I ordered a female 1/4 Jack and a male plug just in case I have some silicone wire ,but I think I will need a wire with a shied ,that I need to order ,I already ordered the red and black wire with Jack's for the leads on each side of the meter no problem,but the center one probe I need or info on how to make one ,anyone have any info please .

[@AERVBlog]

The center probe is for DC only and needs an inline 1 meg ohm resistor. You do not need coax really. It just makes it easier to pull out a ground. In fact you dont actually need a ground wire coming off the 1/4 inch jack at all. Just use the common wire as ground. So tip of the DC 1/4 inch jack connects to a red wire. That wire connects to one end of a 1 meg ohm 1/4 watt resistor and the probe itself connects to the other end of the resistor. --------^^^^^^^^^^^_______________ Probe- resistor-wire from 1/4" jack. Does that help?

[@nor4277]

I just got one.of these meter in the mail today ,it didn't have the center probe with it ,and someone wire it directly a red wire through the 1/4 hole ,so I went for a 1/4 mono make plug for it ,and now I need to find.a.picture of some info for making my own ,if you have any info on that anyone.please let me no and what size jacks are used in the right and left side of the meter so I can order a set

[@AERVBlog]

The DC plug that goes in the middle has to terminate in a 1 meg ohm resistor so if you want to make one just connect the center wire of the coax you use to a 1 meg resistor and the probe itself to the other end of the resistor.The shield of the coax connects to ground. As far as the common and AC/Ohms jacks they are standard 1/4 inch banana plugs and they are straight through, no resistors. I hope that helps. Thanks for watching.

[@ronaldrobinson7780]

what are u calling ur magic box very good video never have seen the mods in one till this

[@AERVBlog]

Ronald Robinson it is one of those little capacitor/resistor/transistor/diode/inductor testers off eBay for $20. I use the thing all the time I just built it into a box. I know it isn't perfect as far as ESR goes but it is sooo much better than what we had just a few years ago and very inexpensive.

[@josephcote6120]

You didn't say, so sorry if you did know. The DC probe has a 1Mohm resistor between the probe tip and the lead. The internal resistance is about 10Mohm, so without the resistor in the probe the DC voltages will come in about 10% high.

[@AERVBlog]

Joseph Cote very true. Thanks for pointing it out. I had to build a probe out of an old scope probe.

[@SDsailor7]

I just bought one of these vtvm and I tested it by attaching my dmm leads to the leads of the power cord ( the one that you use to plug it to the wall outlet) and I got an open circuit. So does that mean mt vtvm is no good?Very interesting video and very informative.CheersRob

[@SDsailor7]

I hope I am wrong and that the vtvm is good. Maybe I am doing something wrong?

[@SDsailor7]

Yes your tester is missing the spring for the D cell battery, mine came with it. I could not figure what it was for and now that you mention it, it makes sense.

[@SDsailor7]

Where did you find the diagram? I could use It.I will add the D cell battery and see if that is the problem. I do not want to hook it up because I do not want to damage it.

[@johnhiggins4698]

What make/model of desoldering tool are you using? Thanks!

[@AERVBlog]

John Higgins it doesn't actually have a brand. it is a ZD 985 I got from Amazon. the deciding factor was price, about $160. It does have some quirks. it plugs up a lot but I can live with it.

[@hassanyael1512]

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[@doriancrosby6850]

@Hassan Yael Instablaster :)

[@hassanyael1512]

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[@hassanyael1512]

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[@warplanner3258]

..any reason you chose AC with a frequency of 1000 Hz?

[@AERVBlog]

Nope. I really should have done it at 400 - 600 Hz if I wanted to do it right. I think maybe it is because that is the frequency default when I turn on the generator. Thanks for watching.

[@EJP286CRSKW]

It doesn't matter. These units can measure AC up to many megahertz. One of the many wonderful things about them.

[@jakelang4387]

mine wont turn on red light comes on but cant meter wont move?

[@AERVBlog]

It is probably the switches. When they go bad the normal result is no output.

[@jakelang4387]

@@AERVBlog im going to get some contact cleaner and clean them inside this weekend..i put new battery in and cleaned that all up..but nothing

[@AERVBlog]

@@jakelang4387 I am sorry. I got mixed up on which video you were talking about. Does the meter move on Ohms at all or is it dead on all positions?

[@jakelang4387]

@@AERVBlog all is dead on the needle in all modes on the switches took battery out that was 60 years old and cleaned it up and put new in...then i plugged it in and let the tubes warm up...but only the red lights come on..

[@AERVBlog]

@@jakelang4387 Looking at the schematic I would say either the 12AU7 is dead or the meter coil is open. There is also a 3.3meg resistor on the grid, pin 2, of the 12AU7 also there is a .005 cap to ground that may be shorted. I would try the 12AU7 tube first. You can test the meter movement by very briefly touching a dead 1.5 volt battery across it and see if the needle moves. Just tap it with a clip lead while the meter is in circuit. Don't leave the battery on for any length of time at all and try to find one that is good and dead.

[@robertparzych7852]

Why the poor focus?

[@AERVBlog]

This video was made before I got a decent camera. It was shot with an old SVHS handicam. Sorry about that.

[@josuelgabriel2497]

ola procuro o esquema elétrico do vtvm sico model 400 obrigado

[@AERVBlog]

I will look in my collection and see if I have that.

[@AERVBlog]

Is that a Superior Instruments or Supreme Instruments? Is it the same as a HP400? can you send me a picture at [e-mail]

[@erin19030]

Is there much difference between the Heathkit models from one year to the next. Most manufacturers use the same circuit design. It's a very clever and hearty design. Accuracy is amazing to for a unit that originally sold for $24.95 the V7A. I prefer my analog VTVM while I'm working on the bench. The digital models are no more accurate and an idiot could operate one.

[@AERVBlog]

I agree. A good analog meter is indispensable if you work on anything that is not purely digital. As far as the meters go there was very little difference between the V7 models. In fact they used almost the same circuit for several years including the big bench model, IMD something I think. I have a senior volt ohmist from the same era and the heathkit was just as good for a lot less money. IMHO.

[@gregjohnson5194]

Bet I know why you got 4 thumbs down - focusing. Great video others wise cool finding that cap turning into a resister and people say you don’t have to worry about ceramics, haha yes you do.

[@AERVBlog]

This was from when I first started to make videos. All I had was cheap a Webcam and an old VHS video recorder. I had a reason to look at this video a bit ago and it made me cringe. It is not often that you find a bad ceramic cap but don't pass them by. Thanks for watching.

[@vancouverman4313]

Here's a useful mod that can be done to this VTVM so it can be used with any conventional probes. www.instructables.com/id/Heathkit-V-7-VTVM-Repair/

[@AERVBlog]

Thanks. I might try hat.

[@EJP286CRSKW]

You want to replace that capacitor again. The voltage rating is 400V, not 50V. First large AC voltage you measure, kapooey.

[@AERVBlog]

You are right. I just looked it up and it is possible to get 150 volts at the input to the 6AL5. Thanks for the heads up.

[@AERVBlog]

I finally replaced that cap with a 450 volt . Safer now.

[@terrycrabtree3779]

I HAVE NEVER SEEN A METER THAT USES TUBES. INTERESTING

[@AERVBlog]

Terry Crabtree they were all the rage in the 60s and 70s. Nothing else could beat the input impedance. The FET, which is the transistor equivalent of a tube, had not been invented yet so most meters could only manage about 100k ohms input. Most were just resistor voltage dividers and they would load down a circuit pretty badly whereas the tube guys wouldn't.