Battery Eliminator Options for Heathkit Vacuum Tube Voltmeters (VTVMs)

I discuss some options for eliminating the need for an internal battery in Vacuum Tube Voltmeters.

[@dblake5356]

A few years ago I restored my IM-18. Besides cleaning it up and replacing out-of-spec parts I had replaced the lamp with an LED and added the "Official" Heathkit VTVM battery eliminator mod following Robert Sumption's KZbin video. With the mod installed I had noticed a "battery" voltage drop in the Ohms x1 setting with the leads shorted but figured it would be find as long as I didn't leave them shorted for long. However, after watching this video I decided to change to the LM317 battery eliminator mod and now there is no significant voltage drop in the Ohms x1 setting anymore. Thank you Jeff for your videos. I find them useful and informative.

[@bubblehead78]

Scary to see bare alligator clips for the IM-18's probes. Great video.

[@kj4daq]

Excellent idea and very easy to follow explanation!! I have two Heathkit VTVMs models IM-11 and IM-18. will work on them to change to self powered for resistance range.

[@eltunene]

Excellent idea and very easy to follow explanation!! I wish I had present-day low drain alternatives back in 1965 when I used to have my Radio-TV service shop.

[@craigdavis1255]

Great video, Jeff. I discovered your channel after buying a V-7 ($20) and an IM-18 ($15) at a hamfest last weekend. I'm going to try a battery eliminator circuit in the V-7 first, which needs to be rebuilt. The IM-18 works but had a leaky battery in it. If I need to use it as an ohmmeter, I'll clean up the spring and put in a battery. Craig KE7MPM

[@pisotones2348]

I went another way with my RETEXKIT VV-1, an european authorized copy of the Heathkit IM-11. I replaced the 1.5V D cell with a 1.5V AA Lithium battery and an AA to D adapter. No more concerns about leakage or durability. These batteries have a shelf life of more than 20 years and a capacity orders of magnitude above an original carbon D cell. Of course, no modifications to the VTVM at all.

[@midmodaudio6576]

Very informative, thank you.

[@youtuuba]

Yes, while the simpler battery eliminator (three diodes, capacitor, resistor) does work well, there is little reason to NOT just go ahead and use the LM317 solution, especially since eBay (and other) sellers make available the ubiquitous Chinese LM317 board with the added external components (e.g. large aluminum electrolytic capacitor) for such a reasonable cost. A couple caveats on the LM317 solution: - At least one popular seller of the LM317 solution used to include a printed installation instruction sheet that accidentally advised connection to the transformer secondary backwards from what would actually work. Make sure you know which side of the secondary is connected to the VTVM's chassis ground and connect the LM317 circuit's input to the other side of the secondary. - The commonly shown schematic for the LM317 solution is very generic and shows two or three components that are not of any use in a VTVM battery eliminator application. As Jeff stated, the two diodes which SHOULD be used in LM317 applications where the output is applied to unknown circuits are not beneficial in THIS application and can be left off. The small value capacitor across the input electrolytic filter capacitor is also not useful. And the small filter capacitor across one of the volt-setting resistors is also optional in this application.

[@williamsquires3070]

With regards to the LED pilot lamp replacement circuit: 1) swap the screw (Edison-base) socket with a bayonet-base socket, the. You can then use the more common #47 bulb replacement as indicated earlier. 2) you can wire D8 in reverse-parallel with LED1. 3) you can use a bipolar (red/green) LED - the two-lead variety - and you won’t need D8 at all. 4) 1 kilohm is more suitable for a 12.6 volt filament winding. For 6.3 volts, 390-470 ohms will work better. 5) finally, if the flickering bothers you, wire a 100 uF/16+ volt electrolytic cap from ground (- lead of the cap), to the junction of D8 and LED1 (+ lead.)

[@Lee_Adamson_OCF]

I used one of those ebay modules on my IM-11 too. Works very well.

[@Pwaak]

Much appreciated Jeff! A while back, a relative gave me an IM18 with massive damage from battery leakage.

[@lelandclayton5462]

I did this to my RCA mater a few years ago. However I used a linear regulator that outputs 1.5V. I also removed the selenium rectifier and replaced it with a 1N4007 diode and a power resistor to account for the voltage difference. I can't remember if there is a pilot light. If there was I think I yanked it out completely.

[@tubeDude48]

I make a kit for this that only requires the 6.3VAC, and will work with ANY meter requiring the 1.5VDC. There is one on Flea-BAY, but has a CAP dangling out the side! Mine comes already made up on a Terminal Strip and mounting hardware with instructions.

[@cocusar]

I ended up using an old cassette-radio thing transformer, and a lm317, similar to the option shown as the 3rd one. I've done that inside my heathkit vtvm 11, fits perfectly. my new hack for it would be to isolate the chassis from the negative terminal

[@thomasheckhaus205]

Hi Jeff, I'm glad I found your channel and I've subscribed. I have a Heathkit IM-5228 bench model. It uses a neon bulb in the line voltage area as a power on indicator. I guess it was to reduce the stress on the 6.3 v winding on the transformer. I also have an IM-18 and a V7A. Robert Sumption is a KZbin provider that discusses the Heathkit design, diode based eliminator. I think he worked for Heathkit. By the way I've been trying to find your Heathkit book. Any idea where I can get a copy? Thanks Tom Heckhaus Retired from The Bell System

[@jefftranter]

Hello Thomas. Yes, I am familiar with that video and it has good information. My book is available from lulu.com ( www.lulu.com/shop/jeff-tranter/classic-heathkit-electronic-test-equipment/paperback/product-21272772.html ) as well as Amazon.

[@thomasheckhaus205]

Hi Jeff, I managed to find and purchase your book and throughly enjoyed it. If you have the time or other subscribers can assist with a few questions I'd appreciate it. I went to a Chinese seller and purchased a few of the "Buck" converters you mentioned. Shipping these days is relatively fast compared to years back It took just over a week and they look exactly as the one in your video. Q-1, I could only find the filter capacitors in a high frequency version. From what I recall we did need high frequency capacitors for radio circuits and they were usually ceramic or tantalum. I've never seen electrolytics in high frequency. The question is can these hf E-caps be used as power supply filters with the LM-317? Q-2, The transformer used in Heathkit and other manufacturers VTVM'S are nearly impossible to replace. Changing the incandescent bulb with an LED greatly reduces the current draw on the low voltage winding. However if any of the components fail in the LM-317 circuit or the diode version that'll be the end of the transformer. Other than a fuse, do you have any recommendation to protect the transformer? A filament or lamp going open would be OK, but if one of these converters goes into a dead short thats the end of the transformer, I'd like to protect that transformer. Any ideas? Q-3 I'd like to buy the other book you spoke of. It seems to be out of print and Amazon is asking $400 USD for one. I checked Ebay and other used booksellers, but apparently the book is printed on gold with platinum ink? Thanks again, I am going through all your KZbin videos, all of which are very informative. Thanks, Tom

[@jefftranter]

Hi Tom. Thanks for buying my book! For a filter capacitor, any capacitor that is rated 1000 uF and 25 volts would be suitable. This would be an electrolytic type. For protecting the transformer, I can't think of any simple solutions other than a fuse on the transformer filament winding and maybe another fuse on the transformer primary. What is the other book that you were referring to?

[@Lee_Adamson_OCF]

Did you have to replace any of the precision resistors on yours? I had a couple in mine that had drifted really badly.

[@jefftranter]

I didn't, but I probably should. One one of the meters there is a 9.1 Ohm resistor that someone replaced with a 10% tolerance unit. These are typically what burns out if you inadvertently connect it to power in Ohms mode.

[@Homer19521]

Jeff - I noticed that one is a 2 wire & the other is a 3 wire (ground wire) supply line. Thoughts? Should the 2 wire be "updated" to a 3 wire? 👍

[@jefftranter]

Using a 3-wire line cord would be better as far as safety.

[@Homer19521]

My B&K 177 is a 2 wire & the B&K 290 is a 3. Measured the 177 chassis to hot & found 109VAC one way, & 23VAC flipping the non-polarized plug. Just gonna put a polarized plug on it & not complicate the ground operation.