VTVM Restoration, Alignment, and why you should own one

This is an in-depth, trouble-shooting, restoration, and alignment procedure involving a knight KG-625 Vacuum Tube Volt Meter. Follow along as I bring this piece of test gear back to life.

[@wesleymatthews137]

I completed my first KG-625 resto inspired by this video. I went a bit further. I widened the ground probe hole a bit to accommodate a grommet, I added a shielded supply line from the selector wafer to the new BNC connector, I added a modern and more secure battery holder, added a new polarized two conductor AC supply cord, added an internal fuse holder, and finally, rubber feet for the stand. The battery holder fit between the original battery contacts and is reversible. I used RG-58A/U cable for the probe. It has a braided core and is soft and flexible. I replaced the cap and a few out of tolerance resistors in the bridge circuit. I calibrated the meter and polished the meter lens with car wax. An old aviators trick. It looks amazing and performs perfectly. Now, on to restore another -625. Fun! Thanks for the inspiration and education, Paul.

[@davidwhelchel8774]

Just to let you know that your video on this VTVM is still o great use and very interesting. Thanks for the content

[@mikemarshall1394]

A trip down memory lane. I built the Heathkit version of that vtvm when I was about 12. I'm 72 now and wish I still had it.

[@xraytonyb]

Another great video! When I was 12 years old, I saved my money for months and ordered a Heathkit VTVM that is almost identical to the KG-625, even down to the mounting bracket! When I built it, I only had a low-end 20K ohm/volt multimeter to do the alignment (12-year-olds are inherently poor). I remember doing those unsafe alignments on the AC. I didn't even have an isolation transformer! I used that meter for many years. It is now packed away in my storage unit. I think I will take it out and give it a proper restoration after 35 years. It still looked like new when I packed it away many years ago as I worked so hard to be able to buy it and take care of it. Thanks for inspiring me! Keep up the great videos!

[@MrCarlsonsLab]

Hey, That's great! I would love to hear about the resto process! These really are great meters, and fun to restore. Thanks for the comment xraytonyb.

[@boulder89984]

The man can smell an electron that's gone the wrong way. Amazing troubleshoot.

[@williamstarklauf6085]

No a electron that has gone wrong way is identified buy the rainbow flag

[@vernonbosshard9317]

You sparked a renewed interest in tubes for me, and I'm old enough to have taken tubes out of the family TV and carry them down to the local drug store to test and buy new tubes. But they did not teach us a darn thing about tubes in tech school, all I know is they are voltage amplifiers.

[@erin19030]

I'm a well seasoned professional electronics technician , my education goes back to 1961 at RCA Technical school. While in the Army I studied Radar, and missile guidance systems. I watch your tutorial video's as a refresher course. Your teaching methods and circuit understanding are excellent. During my teen years I did kit building of EICO products. While going to RCA tech I worked as a wireman for GE, a skill that has gone the way of robots. Now in retirement I build Experimental circuitry and revitalize vintage electronics. With all my experience I still learn something new each day. Keep,up the good work Doc!

[@brucejenner4800]

You remind me of my Father. He was in the British Army in the Artillery. At the time the Artillery were developing missile systems. My Father was into electronics, I remember looking at all the trays of components, screws, and most of all, remember the smell of solder! He was a subscriber of the Practical Wireless magazine, and made all sorts of projects from its pages.

[@sonyxperiathree4554]

I love your tenacity and attention to deal. I broke my leg, a watched all your excellent videos as I just sit idle waiting for some healing to occur. You are one of the last true omni - knowledgeable electronic engineers. Thanks for the experience and knowledge you convey on KZbin.

[@iamhe999]

It doesn't get any better than this folks... Kudos to this great electronics teacher....

[@jimmymac5012]

I have to say I am a big fan of your channel. Excellent presentation and knowledge of your trade. My hats off to you sir.

[@MrCarlsonsLab]

Thanks Jimmy Mac!

[@johnwest7993]

Clear and complete description, and all the knowledge of an old-timer. I get the impression you started learning electronics at a very early age, and were taught by a master.

[@dancamp1515]

just watched the Forest Service Radio video, and then this one popped up in my suggestion box. "Hey, I have that VTVM!" Thanks for the great overview, I now have a better understanding of one of my pieces of test equipment.

[@paulk.bowden7134]

Back in about 1952 I built a Heathkit VTVM that is still working fine on my bench. I did switch out the tubes for solid state equivalents. They plug into the tube sockets. This was the first of about a dozen Heathkits I’ve built.

[@mikesteffes9999]

Same here, except I didn’t build mine until about 9 years later.

[@DucatiMTS1200]

You have what it takes mate to be deservedly called a great electrical engineer.

[@marklowe7431]

KZbin should conduct awards for channels this good.

[@tashpaug]

Mr. Carlson, I am once again impressed by your ability to repair equipment. In this throw away society it is so refreshing to see someone who rebuilds equipment and thinks through how to find and fix problems. Excellent video, keep them coming. Tony

[@MrCarlsonsLab]

Hi Tony. Thanks for the comment. I'm working on the next video right now.

[@Mork007]

Super video. As an amateur radio operator I have to say you have one of the best channels I have ever seen. Thanks for all your effort in the videos. Jim

[@MrCarlsonsLab]

Thanks for the nice comment Jim!

[@arthuruzi2759]

q

[@arthuruzi2759]

a

[@keithstudly6071]

AUH, A-jil-lent? I have been familiar, for years with units that looked like the one he was pointing to and some were H-P and some were A-gi-lent but this is the first time I ever heard of A-jil-lent. Mr. Carlson you teach this old dog new tricks everyday! Thank You!

[@davidprice2861]

Fancy some stray bits of steel wool messing it all up. Excellent video as usual, very thorough and informative.

[@TJSurma-se6dl]

Thank you for your efforts in putting together these videos. The quick 'aside' tips offered up throughout are gold. I often reach for a larger 'gun'-type soldering tool when working with a component that will sink/pull the needed heat away from the solder joint. I would have never thought of replacing the tools standard/long tip element with a short piece of 10 gauge copper wire. So simple, yet effective. Brilliant!

[@MrCarlsonsLab]

+T.J. Surma Glad your enjoying the video's T.J. Thanks for the kind words!

[@bassman7115]

Thanks Mr. C. I have two RCA VTVM's; WV-87B-Master and a WV-98c Senior. Both have been restored to their former glory thanks to your video's and Patreaon channel.

[@MrCarlsonsLab]

You're very welcome!

[@erichgugle5500]

Another great troubleshooting and alignment demonstration. Very nice find in the chassis mounted Variable Resistor with the steel wool hairs inside causing the plates of the 12AU7 to be incorrect. I am extremely impressed with your skills.

[@robbo6460]

Another excellent video. Thank you Mr. Carlson. I've done several calibrations on Heathkit V-7A's and this video has taught me I was screwing up the red dot adjustment by following the manual. Now I know. Thank you

[@MrCarlsonsLab]

Glad to help Rob!

[@robbo6460]

@@MrCarlsonsLab what is that voltage adjustment dial please?

[@Andre-on5kr]

I found this video very helpful for restoring my DeVry VTVM. Your description of the processes will be invaluable to me. Thanks, mr. C!

[@paulmichaelson7203]

This reminds me of my old CONAR VTVM that I built when I was a student at NRI. As I remember that meter only had one tube. I remember when I visited NRI they had a bench with about 50 tubes being de-gassed in preparation for use in their VTVMs. They had them running with the filament energized and no voltage on the grid or plate. I used that old CONAR meter for many years until I finally got an FETVOM that had an analog meter. That VTVM was a great instrument. I think the Knight meter is probably a better design. I have always loved analog meters. Very useful. Another very enjoyable video, Thanks for the memories Mr Carlson.

[@vasilification]

" A problem well stated is a problem half solved" Charles Kettering Excellent video, a key learning point is the set up Mr. Carlson does before starting the repair. Careful analysis of the problem, from how to remove the meter from the case, the cord the rubber grommet, looking at the condition of the unit, studying the schematic, understanding how the unit works and determining the approach for repair. The net for me is to slow down and familiarizing your self with the problem before beginning the work, which will may make the restoration more enjoyable. I watched the video before starting my restoration of a vintage Hickok VTVM, definitely helped.

[@magic1bean]

Back in the 80's I was a bench tech for HP. One of the other techs had an HP VTVM that he could not get to pass specs at high end frequency. The fix was drilling the rivets out, sanding the mating surfaces and riveting the pieces back together. FYI, in case it helps anyone else. Worth trying the antisieze first tho. I really have enjoyed your videos. I learned on tubes in 1968 and have had a great trip down memory lane while learning.

[@Screamingtut]

i had the heathkit VTVM plus someone gave my dad an Eico VTVM which I repaired I was 15 at the time I am 62 now LOL enjoyed the video

[@dhansel4835]

WOW I built one of those decades ago and still have it. I don't use it but it brings back memories. I guess one day when I can get into that closet I will open the door and see what falls out. Thanks....

[@MrMoggyman]

Beautiful and useful piece of kit for RF sections. Had one in the radio workshop. Ours was Heathkit.

[@BrandonHall916]

I never thought I would be so excited to see someone calibrate something, GREAT JOB!

[@MrCarlsonsLab]

+Brandon Hall Thanks Brandon!

[@benthere8051]

Very well done. I enjoyed following your thought process. Finding the steel wool in the pot is a great example of why you can't make assumptions when troubleshooting. It is sometimes the most outrageous circumstances that are hardest to find. That is also a VERY good reason to be very careful with steel wool around electronics.

[@erin19030]

I've been an electronics tech Ian since 1961 and like to consider Mr. Carlson' videos to be great refresher and continuing education courses. I have the HealthKit version of this meter.

[@bjornhalstrom9933]

KZbin had unsubscribed me. A number of creators are experiencing this. Interesting video. I wish I had one. In high school electric shop we built vacuum tube circuits. Later when my brother came along they were building transistor circuits.

[@edvaioli7340]

Thanks so much for this. Using your video as a guide I was able to restore the flea market RCA Volt Ohmist I scored for $5.00. The RCA is essentially the same as your Knight and your explanation of the bridge circuit was the key. I too had a 12AU7 that was way out of balance along with a couple caps that had drifted badly. Thanks again and keep up the excellent work!

[@MrCarlsonsLab]

You're welcome Ed!

[@AB1Vampire]

@@MrCarlsonsLab I was about to write the same as Ed (above) so I'll put it under his thread. I'm also renewing an RCA VOM. It's the Voltohmyst Junior model. It has the same 2-tube bridge circuit. Thanks Mr. Carlson!

[@barquisimetido1]

I have a vintage Heathkit VTVM model V7-A and have noted that it, the Heath IM-18, Heath IM-28, EICO VTVM's, this one and others of about the same era uses the same tube numbers and schematics in general with a few different values and cosmetic variations, but in essence is the same instrument design (electronically speaking).

[@rlamb51]

Very interesting part number breakdown of the vacuum tubes. I worked with them for years but didn't know how the numbering worked. I knew the first numbers were filament voltages but the rest was just a designation. Goes to show you that you are never too old or experienced to learn something new.

[@MrCarlsonsLab]

Thanks for the comment Roger! Glad you found this interesting.

[@MutethatBozo]

Watching this as I am working on some minor repairs to an old DeVry vtvm from 1955. Thanks again for the videos, and peace :)

[@chrismckenna4689]

Really nice! I'm new to electronics, but with the help of this video, I just restored a DeVry 1S14 VTVM. Some caps, some fixed solder joints, and it works great! I just wish you lived next door so I could pop over and learn more stuff!

[@MrCarlsonsLab]

Glad this helped Chris!

[@chrismckenna4689]

Do you have a video that explains what test equipment one should acquire, and in what order, to work on older ham radios?

[@tuckermoreland147]

at one time i had a complete set of sencore tube testers, an eico oscilloscope. signal generator, isolation transformer, capacitance tester, vom meters, variac, flyback transformer probe, and other things. got divorced and lost it all. those two oscopes you got for 5 bucks apiece reminded me of the eico. didn't surprise me they still worked. your ability at troubleshooting is amazing. i can watch you at work for hours on end. i wasn't anywhere near as good at it as you. but with a schematic i fixed a lot of stuff. mostly audio stuff. a problem i used to run into was some instrument amplifier manufacturers would use components ordered with their own number printed on them. wasn't difficult to find the problem but made it difficult to cross reference a replacement and a component might be worth a few cents but ordered from the manufacturer would cost many dollars. with your ability you can probably figure it out for yourself. i wasn't that gifted. you are an excellent teacher. i have learned more watching you than i ever did in electronics school. i was certified for radar and communications back then but never worked in the field so i wasn't a complete dummy. i am retired now and during this pandemic i found you on the internet. it's true u use it or lose it. but audio is pretty simple and i would like to get back to that. keep the vids coming and i'll keep watching.

[@oldschool-68]

Thank you for being on KZbin. You have taught me so much in a short time. I've tried reading books and QST magazines to learn more stuff but get confused more than anything. You on the other hand are my "guru" so to speak. I've been a ham since '93 and I love to tinker. I just love your style of presentation the most. Thank you and 73s. KB5WUF

[@MrCarlsonsLab]

Thanks! Glad your enjoying the video's.

[@absurdengineering]

Oldschool68 Unfortunately, most authors have some gray area in their knowledge so they can’t but gloss stuff over, and/or they simply have no knack for effective communication to the reader. There’s a lot of cargo cultism even among people who do engineering, so a lot of written text seems impenetrable: the problem usually is not with the reader, but with the writer.

[@cristrigotti9933]

I just got one of these at our club auction for $7! I followed your video and changed out all the resistors and followed very closely you cal procedures. It is all cleaned up and working very well. Thanks for doing your videos.

[@ThePapa41]

What a fine tutorial on the restoration of the Knight VTVM meter, you have included so much education along with the restoration! Your work is outstanding! Louis

[@BellTechnical]

I enjoy every second of your videos. Thank you for the vacuum tube lesson and theory of operation. I grew up with late 1970's heathkit projects in place of sports. While discussing vacuum tubes I had childhood memories of tube testors familiar at hardware or drug stores. We've come along way with solid state components. Thank you for your channel I appreciate your patience and great narratives. Keep up the Great work!

[@MrCarlsonsLab]

Thanks for your kind comment!

[@filijavilija]

My grandpa had this exact same meter to repair TV’s he was a TV repair man back in the day. I remember playing with this meter when I was a kid back in 1976 .

[@restoredoutboards]

Hey Mr. Carlson! Thanks for this video. I just finished bring one back to life thanks to you. Replaced a couple of resistors and cleaned the pots, etc. works like a dream now. Pretty good investment for 15 bucks. Thanks so much for your videos and sharing your knowledge. Inspiring.

[@MrCarlsonsLab]

Glad to be there Greg!

[@davidmaddison2628]

I love your videos and repair and restoration techniques Mr Carlson. You also show that old equipment can be very good.

[@geraldwellborn5047]

I have a RCA solid state VTVM (although no vacuum tubes in it) I bought in 1973. It has been stored away for 40 years or more. After watching this, I believe I will dig it out and change its battery and verify its accuracy. Very enjoyable video Mr Carlson. Thank you very much.

[@CraigHollabaugh]

Hey Mr. Carlson, I now have 3 VTVM's, EICO, Senior VoltOhmyst and Conar (through estate sale buys). This video is just what I needed to kick my butt in gear and get at least one of them running. Thanks. Craig PS. killer tips here: bounce dryer sheet for meter face de-static and Weller 10AWG tip. Thanks for these little gems

[@MrCarlsonsLab]

+Craig Hollabaugh Glad your enjoying the video's Craig! They all sound great, choosing the candidate would be a hard choice. I have an EICO with a huge meter that I would like to have working as well. Good Luck!

[@The1jonnyz]

I ALWAYS learn something new from your videos Paul. Another great presentation full of tips, tricks, and knowledge!

[@MrCarlsonsLab]

Glad to help!

[@jlucasound]

I Loved it. The techniques you have demonstrated can possibly be used on other devices. (Barring any specific requirements, i.e. aligning a graticule on a scope vs. the needle on your meter). The trouble shooting and calibration and safety tips you teach are very clear. Thank You, from (almost) 5 years later!

[@jimthannum7151]

Wish I never gave away my VTVM! This was an excellent tutorial, so clear and understandable, and a great learning experience, not just the restoration, but your superb troubleshooting technique.

[@TachiTekmo]

Oh, boy, does this bring back memories! My dad had one of these in his "shack," and was constantly fiddling with it. I remember being - oh, six or seven years old - and "helping" him by handing him resistors and what-nots as he'd work on his ham radios. I love these "old-fashioned" VTVMs with the big sweep indicators and solid "ka-chunk" switches! Thanks for bringing this one back to life, and may she serve you long and well!

[@MrCarlsonsLab]

+Tachi Tekmo Thanks Tachi!

[@82abn34]

Thanks, I didn't understand the bridge circuit function on my Heathkit V-6 meter. This meter restoration is my first journey into the world of vacuum tube technology. When you build something, you really find out where your knowledge gaps are. I've had this thing for a couple of years and it keeps getting pushed to the bottom of the pile but I should have it completed soon.

[@bugdrvr]

A few days after I watched this video I found a sad Heathkit V-6 VTVM in the "junk" pile of an estate sale. After some cleaning, polishing and replacement of a few bits it's now a proud member of my workbench. Thanks for the inspiration!

[@MrCarlsonsLab]

Glad to be that inspiration Jim!

[@icyrax314]

Found out about you a few days ago and I must say I love the depth that you go into what your talking about.

[@MrCarlsonsLab]

icyrax314 Thanks, Glad your enjoying!

[@CraigHollabaugh]

Mr Carlson, I spent about 3 hours fixing another dead VTVM today B&K 375. Finally found that the 'ohms' pot wiper was internally shorted to the shaft, hence also to the frame. This threw off the PS voltage, the bridge bias point, and just about everything else. I pulled the pot's cover, and reseated the wiper on the phenolic, put it back together and bingo, works like a champ. I suspect this VTVM was never used, yay, brand new meter! Thanks again for this video, I wouldn't have spent the time today otherwise. BTW, this B&K VTVM has great meter with a geared changing scale. Replaced my Voltohmyst. Have a great day!

[@MrCarlsonsLab]

Great to read Craig!

[@KG5IF]

I never knew the significance of the last digit in a vacuum designation till now. Been working in electronics for 50 years. Thank you sir. Like your B+ warning too for the new players with tube gear.

[@waynecarlson3736]

Once again Paul outstanding as always. I recentl bought this meter and will bring back to life AT MY OWN RISK Thank You

[@TubeRadioRepairRestoration]

I love your videos. Your so intelligent and I'm learning alot from you ( happy patron). One of the things I love most about your videos is they are very comprehensive and just one part. No BS just trouble shooting / repairing in one video, not stringing along with multiple videos

[@DuhBiggestDog]

Mr. Carlson you continue to amaze me. Every video you do is a work of art. I'm a gray beard from the vacuum tube days and your knowledge of and the clarity with which you describe these circuits are exceptional. Would love to have an eyeball QSO with you someday .73,DonK2PMC

[@MrCarlsonsLab]

+Don K2PMC Thanks for the kind words Don! Glad your enjoying the video's.

[@gchalljr]

Thank you for creating the video on VTVMs in such detail. I am getting ready to restore a couple of VTVMs and now I feel I understand the circuit balancing. The way you explain things is awesome.

[@MrCarlsonsLab]

Thanks for the comment Gary! Many more video's like this coming.

[@satellite_guy3768]

A really super duper video!! Presented this way and to this much detail is the way they should be done. A very excellent tutorial. Thanks so very much for the education and insight to an almost lost and forgotten art!

[@MrCarlsonsLab]

Thanks satellite_guy for the nice comment!

[@clytle374]

Another great video, with great advice. I found one a while back in an antique store and bought it. Just got done getting it working, building a probe for it now. I think it had the original dry cell in it. Corrosion was half an inch deep, but still had 1.49 volts. Only question i had was finding coax for a probe lead. Hard to find anything with a rating that really gave me a good feeling about holding it in my hand and probing HV with it. Thanks again.

[@bborkzilla]

For heavy soldering I use a Weller iron normally used for soldering stained glass windows. I picked it up at a hobby shop for cheap. It's also good for soldering PL259s.

[@sincerelyyours7538]

This makes a really good first time tube project. I probably paid too much for mine but I got one in nearly pristine condition. I think the previous owner had trouble aligning it so he stopped using it. Almost new inside and out, the few very light scratches disappeared easily with a bit of plastic rubbing compound. That creates a lot of static but Staticide sheets (from Amazon) gets rid of the static buildup without leaving a soapy film on the plastic. All resistors were more than 20% off their markings so they all got replaced. The bias pots were 20% out as well causing a lack of range in the alignment. Had to rebuild the 1.5V 10K pot with parts from a Fender amp bias pot which are the only ones I could find still available online. A final bit of work repairing the probe tip and she's good as new. Thank you, Paul for your excellent video! Thanks to you, antique electronics restoration has become my new retirement hobby.

[@MrCarlsonsLab]

Thanks for your kind comment! I'm glad you found a great hobby!

[@MrUbiquitousTech]

Great job on restoring that VM! I'm seeing the trend here, when you're done with a piece of equipment it looks as good as new and works even better! I like your attention to detail. Nice work on diagnosing and repairing that VR; it's not as easy as it looks when you're doing it, it takes knowledge and experience to accomplish that.

[@TheLawrenceWade]

Yeah, was that a tin whisker forming in the VR? Something like that? It seems more likely than steel wool, especially in old high voltage equipment.

[@vancemyers8286]

@@TheLawrenceWade Would a razor help???

[@PurityVendetta]

Great explaination of how the bridge in the meter. I have normally used AVO 8's as my analogue meter as they've served me well over the years. I can't actually remember how many I have but one, ex Royal Navy has the kit with the high voltage shunts. After watching this video I think I need to add something like this to my bench. Thanks again.

[@johncunningham5435]

Very nice demonstration of what you can accomplish when it comes to old vintage equipment that in my view does not get enough praise. I believe as you do; they have a place on the bench. I recently scooped up a Sencore FE20 Field Effect Multimeter in mint condition. The only major concern was the meter was pegging, which required the removal of the front plate and surgically correcting the issue. Then I used a 1% 100 mega ohm resistor and bingo it was right on the mark. There is nothing more satisfying when you bring back a vintage treasure to life and show it can still stand up, congratulations on a superb video.

[@MrCarlsonsLab]

+John Cunningham Thanks for the kind words John! Sounds like a great job on the Sencore.

[@davideppert6486]

Thanks for taking the time to go into so much detail in your videos. It really does help us beginners in the learning and after a while many of the points you discuss just start falling into perspective.

[@MrCarlsonsLab]

+David Eppert Glad to help Dave!

[@xenia5101]

Great stuff. 55 years ago I was using a similar VTVM (RCA) as a high school student to troubleshoot radio and tv gremlins.

[@RestoreOldRadios]

Another excellent video! Your presentation skills are excellent and your knowledge is superior. Glad to see you promoting safety too. Best. Don

[@MrCarlsonsLab]

Thanks for the nice comment Don! Glad you are enjoying the videos. You have great videos yourself! That Silvertone 4569 is beautiful!!!

[@fredclark4033]

Great to see how accurate the old vom meters really are even today.

[@naknakacknak]

Excellent video. Very informative. The attention to detail is appreciated.

[@waswestkan]

Great video thanks for creating it. Over 20 years ago I had the chance to grab a pile of VTVOMs for free, now I wished I did. During an extended illness and other life events My Eico FETVOM was relegated to storage by family that didn't know to remove the batteries, by the time I got to it there was a corroded mess inside.. Than again the VTVOMs would have went into storage as well and could have suffered the same fate. Whet I went to tech school the Eico FETVOM was our soldering instruction learning lab. We where taught wiring junction was supposed to be both electrically and mechanically secure before applying solder. To pass that point in school we had to to bend component lead and wiring around terminal strips and other connection points. we had to show that to the one of the instructors before applying solder. When using the house wiring to calibrate the AC range, it's a good idea to ask one of the power line crew what voltage to expect, if you talk nice they will help you calibrate to one of their meters. An isolation transformer would be great , but many will not bother to attain one , but they can sill be safe. No doubt somewhere on the web there should be instructions on how work safely with line voltage and the even higher voltages inside vacuum tube equipment

[@MrCarlsonsLab]

waswestkan Thanks for your comment!

[@tomwoehle3519]

Much appreciated your educating style. Will continue my schooling during retirement.

[@greggaieck4808]

Mr Carlson your cabinet of your VTM is in good shape the cabinet looks like new that's cool

[@ppdan]

I am amazed how little editing there is on your videos. Takes some great skills to narrate like that. Very good job, keep on the good work!

[@MrCarlsonsLab]

ppdan Thanks for the nice comment!

[@jeffryblackmon4846]

Now I want another VTVM. Thanks for a fine, detailed video presentation.

[@MrCarlsonsLab]

Hi Alan Janover. This response may not be in order to your post as you do not have a reply tab under it. You may need to go into your G+ settings and edit your circles to "Anyone" Then the reply tab should appear under your future posts. The reason I didn't use the battery for calibration is, the scale on the Knight only goes to 1.5 Volts. A new battery is "1.6 Volts plus" and would create an error factor, even if aligned to the red dot. The .5 and 1.5 Volt supplies are taken from the Voltage divider that I did show on the schematic a number of times. "The accuracy of any meter is only as good as the alignment." LOL, I will try harder next time to get my camera in there to get the glow of the tubes. Thanks for the comments!

[@MrCarlsonsLab]

+Dewey Rayburn Your welcome Dewey, glad you enjoyed!

[@mitchlee3008]

Your information about the ground on the input jack was dead on for the Knight KG-625 meter I just received. A simple ohms check revealed no connection between the ground and the tube support bracket. Gonna give this meter the once over and try to find the missing bracket and probe, or make them. Thank you for what you do Sir, from a fellow Canadian born man who loves in Florida now. Cheers!

[@valakatz3967]

Thank you Mr Carson great video like always! I am going to work on mien now..

[@stevedonahue2517]

Really thorough video- I like how Mr Carlson takes you through his troubleshooting steps, and how he located the poor mechanical ground connection. It was a real treat to find any video on Knight Kit equipment. Bravo!

[@MrCarlsonsLab]

Thanks Stephen! I do have some "rare" projects coming soon as well. Glad your enjoying the video's.

[@podxtv]

Really enjoy your videos - anyone studying electronics repair should watch these

[@bobkins270]

With out this video I would have never have calibrated my Knight VTVM. It was the 12au7. I just replaced both tubes, and it calibrated beautifully. Thank you for going though the steps and explaining the problems that could and did arise. I appreciate the videos. Thanks again Brad

[@MrCarlsonsLab]

Glad the video helped Brad!

[@ele4853]

This one really made me learn a lot about these meters. Thank you so much for your great job at teaching! I tried to find one to buy with no luck...

[@MrCarlsonsLab]

+Really? Your welcome..... Really! :^)

[@Daveyk021]

Picked a KG-625 VTVM up on Ebay last week. No issues balancing it at all. When I took it apart, I found the negative lead of C6 was making contact, but not at all soldered! Its ESR was 3.0 Ohms, or slightly greater. I replaced it with a 20uF 200v (Sprague 500D206F250FJ7 ) from my old stock that still checked ~24uf with a ESR of about 1.5 ohms and it is working fine. I am really happy with this old meter and will make a great addition to my antique work bench that I am building. I'll stick with my Fluke 87 for precision resistance measurement though 8-)

[@denniswalsh8476]

I have (or had) a mid/late 60s Heathkit VTVM I put together when I was a kid. I recently though I could use it in my shop and though about trying to find it. After seeing this I HOPE it's in storage and not tossed out.

[@hadireg]

one of the greatest videos! a concentrate of teaching in one video! Thanks Paul👍👍

[@kellingc]

I can't believe I watched that who;e thing. Great video. I want a VTVM, now.

[@laser31415]

twice

[@denniswalsh8476]

The second kit I ever built was a HeathKit VTVM in about 1966 or so. Somewhere along the way it got lost or tossed. Wish I still had it (mostly nostalgia). I'm an electronics pack-rat and can't think of any reason I'd toss it rather than repair it and put it on a shelf.

[@elanducanada]

Another great video Paul! Thanks!

[@nigelkingsley-lewis534]

When I saw that short was in the Pot my first thought was tin whiskers. Many years ago I was shown how to quickly get rid of tin whiskers in pots and switches by an old TV service engineer. He kept a single cell lead acid accumulator for the job, a lead to the case and another to the contacts and the whiskers were gone in a flash, saves trying to take the pot apart, very often the tabs break when re-assembling.

[@MrCarlsonsLab]

+Nigel Kingsley-Lewis Thanks for your comment!

[@garybevis8691]

Excellent old school tactic, use low voltage high current to vaporize the whiskers shorts! Dang what an elegant and effective solution...Now where to source a single lead-acid cell...lol

[@1flatlander380]

@@garybevis8691120/18VAC transformer, Bridge rectifier, LM317, four 0.1 Ohm 5W resistors, four 2N3055s, SPST momentary switch, and a few other odds & ends.

[@jackiefarmer4892]

What a pleasure to hear the word "SOLDER" pronounced without the silent "L" !

[@danmackintosh6325]

Indeed, it's nice to hear someone so knowledgable and whom doesn't partake of "soldermy" haha

[@budboggy4699]

I think it's a Canadian thing, eh? It causes him to mispronounce Farad as FAYrad, too. The guy's name was Faraday: Fare-aday, not Fay-raday...wonder how he pronounces "soldier"? Not a bit of that is an issue here though. His amazing teaching skills, along with an extraordinarily extensive understanding of broad and diverse technologies trump his localized pronunciation idiosyncrasies.

[@petenikolic5244]

@Ken Mason soLder :-) ..

[@DaleDix]

Amen

[@oldbatwit5102]

Solder doesn't have a silent L.

[@frankcollins5109]

Just wanted to comment on the clear and excellent presentation of all your videos. This one takes me back 50 years from when I left school and started work as a trainee in a radio and TV repair shop. It was all valve (vacuum tube) technology then so I can really understand and follow your projects. I remember building my own valve receivers and AM transmitters. Those were the days! 73's de G0RXO

[@MrCarlsonsLab]

Thanks for your comment Frank!

[@roygarcia7835]

i loved this so much i grabbed an Eico model 249 that i got in a bunch of equipment that i knew wasnt working. i purchased all new Capacitors and replaced the 1 electrolytic. Once i was done i fired it up just to see if anything worked. Well then i tried a few other things and came to realize the actual meter was faulty. Although it didn't go as planed i still had fun and now will be searching for another Eico and keeping my eye for a good deal to end up with a nice VTVM. I just want to thank you for motivating us to bring life back to these awesome machines. Also for showing us how to do it and teaching us in a manner an amateur like myself can get a grasp. Being a visual learner these youtube videos make my life easier lol.

[@MrCarlsonsLab]

+Roy Garcia Glad your getting into some of this old gear Roy! Thanks for the comment as well!

[@DennisMurphey]

my second viewing of the because now i own a Knight VTVM a different style more upright, but i learned this time about the need to isolate questionable bits and retest. Really useful thank you, just abut everything i have seen from your work is so useful and well done. thank you, D

[@harrystevens3885]

I wish I had discovered your videos a few years ago, for me the best KZbin channel ever, the wire wool strands found in the VR was a weird one, another enjoyable watch just brilliant in fact ....thank you!!

[@MrCarlsonsLab]

Thanks for the kind comment Harry!

[@willyrivero470]

What an awesome array of all kind of meters you have. I'm a technician and also a collector of meters, just love them even the old analog meters, but not even close to your collection 😁.

[@johntriplett848]

Your ability to blueprint electronic gear and show the process on video is motivating to the extreme. For example, you not only showed how to locate the zero adjust problem area, you showed how to fix the problem. You took the potentiometer apart, observed the steel whiskers that were causing the short, cleaned them out, and put the pot back together - problem solved. Thank you.

[@ganko2240]

Excellent Video! I have a 620 in line to get worked on and this video will help getting a handle on the schematic and theory of operation, I read somewhere that these used to be sold as kits.

[@MrCarlsonsLab]

Pablo Padilla Thanks for the comment Pablo! Glad this video is helping.