A Deep Dive Into Heathkit VTVMs, Using the IM-18 As An Example
Вставка
- Опубліковано 3 лип 2024
- I have been restoring vintage VTVMs (most of them being by Heathkit) over the last several years, and have gathered a fair amount of experience and knowledge about them and their workings. I decided to put most of that into this single video documentary in order to share it with others. I also include complete details on how to make a suitable battery eliminator that works well with the Heathkit lineup of VTVMs.
The latter 2/3 of the video features my newly CAD drawn schematic/documentation package, and the PDF of that may be downloaded here:
www.serpentwebsite.com/filesh...
with the IM-18 link near the bottom of the page
Here is a timeline table of contents for this video:
00:00 Introduction & history
05:48 Opening the typical Heathkit VTVM case
06:21 Internal overview
12:06 Restoration (things that commonly need attention or replacement)
19:09 Battery eliminator
29:58 Vacuum tubes
33:34 Test leads
35:05 Calibration
46:35 Schematic diagram & circuit theory - Навчання та стиль
Incredible work. I can hardly imagine the number of hours it took to draw and organize that schematic -- the schematic Heathkit WISHES it had included at the time! (Though I understand theirs is geared toward the kit builder and not someone trying to deeply understand the circuit.) Bravo, sir.
Ward Co, you should see the schematics I did before I retired, also in AutoCAD and in the same style/sensibility. Many were on large [
(5 or E sized) paper and often ran to hundreds of sheets. This one is less than a day, actual drafting time. Of course, doing the research and making layout sketched, and checking my work, all that took a lot longer.
Thank you for sharing restoration details plus a detailed circuit explanation. I found it very useful since I'm currently in the process of restoring an old RCA's WV-98A, which is basically the same circuit than Heathkit with minor differences in bridge bias. Your truly educational video simplified me a lot, particularly the cumbersome RCA's drawing which includes rotary switch representation instead of an real electrical schematic as you did in CAD. Battery eliminator is a must i think, and also recapping. I'm also replacing the old solid state selenium rectifier by a modern silicon. I'm also going for NOS replacement tubes. I'm concerned about many old carbon comp resistors ageing, so I decide to test them, just in case. I've no idea about filament secondary coils current capacity, but this model does not have a light bulb but a neon bulb across line voltage, so I'll assume there is room for extra current for battery eliminator.
Thank you for your extensive presentation which I haven't found elsewhere. I'm restoring 2 IM18 models, a VTVM and the British made VVM variant. The DC calibration is trying on my VVM. Your theory part seems essential to me in order to make the VVM work with precision again.
Great job, and much appreciated
This is an impressive study on Heathkit VTVMs. I did a restoration for V7a which is a very similar one.
The heat current capacity of the tansformer is 800mA instead of 80 mA which is as shown in your drawing.
Along with LM317 battery eliminator, I also replaced the bulb with an LED to save more current.
This was my same question. Thanks for answering.
Thanks alot.
On your fine schematic, I'm thinking bullet point #5, AC Balance, under NOTES ON THE CALIBRATION POTENTIOMETERS, sentence 2, should read "Adjust the AC balance pot" and not "Adjust the DC Balance Pot" eh?
Great detailed breakdown. Could you tell me where the other end of the bare braided wire that connects to the battery spring hub connects to? The one I have in flying in the breeze.
2aprotectsallothers592, I don't recall there being a bare braided "wire" in any of these VTVMs. Perhaps that is something that was added to yours by a previous owner.
Hi Is that a Electrolytic capacitor next to diode, Mine had a non, but someone changed them.is that wrong
Hi, thx for detailed explanation.
I did not need but it has been fun to watch anayway.
PLEASe, take note.
From everything I know and do educated guess, OUR own industry NEVERE EVER used "East Germany" when it comes to making markings on ANY ouf our often high quality made products sold under any brand on earth. Worst case it was labelled "GERMANY". Normally it was "Made in GdR".Hergestellt in der DDR".
Look for the unique 1 in a triangle and the Number "1" ienclosed by a Q Symbol. Those indicate original, made in the GDR HQ tubes.
THX. BTW. You might habve noticed, it was NO EAST GERMANY.
Please respect, it was the "German Democratic Republic" (abbr. GdR/DDR german))
PERIOD.
No excuse for using the wrong, often hatefully & devaluating used speech of the cold war.
Read many Tube related forums, ask the users for RFT Mühlhausn ans Erfurt factory GDR made tubes.
You will hardly not find complaints if any at ll.
THX
I own a Heathkit vtvm IM-32
In some v.t.v.m.’s, the positive
contact is grounded. In other instruments, the negative contact is
grounded. Source : page 197 of Vacuum-Tube-Volt-meter-VTVM-How-it-works-How-to-use-it-Rhys-Samuel-1956-254p.pdf
have you the schematic for the battery elliminator?,thanks.
paul.alarner6410, have you watched the video and read the description? The battery eliminator schematic is shown around the 1:43:35 time mark, and the downloadable schematic is also linked in the description.