Great video, but most importantly, thank you for the redrawn schematic and explanation of operation. I routinely restore V-7/IM-18s as gifts and for auction for the local radio club, and I have 5 set aside that do not fully work correctly, and plan to dive into those now utilizing your schematic. The usual failure is that the AC ranges do not zero, or require large zeroing inputs across the ranges. I think I now see what resistors I need to target.
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 sketches, 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.
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.
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.
I'm surprised that you didn't make any mention of the IMA-18-1 solid state replacements for the 2 tubes. I've had them installed in one my SM-5228 VTVM's since the late 70's, the other I have I kept original. Still have another NOS set stashed somewhere in the lab that I've never used. I use the 5228's for alignments and have the HV probe for checking CRT anode voltages.
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.
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?
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 found an IM-18 amongst my late fathers possessions. It doesn't mean anything to me, but I would love it to go to a good home. Would anyone be interested in it.
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
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.
Great video, but most importantly, thank you for the redrawn schematic and explanation of operation. I routinely restore V-7/IM-18s as gifts and for auction for the local radio club, and I have 5 set aside that do not fully work correctly, and plan to dive into those now utilizing your schematic. The usual failure is that the AC ranges do not zero, or require large zeroing inputs across the ranges. I think I now see what resistors I need to target.
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 sketches, 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.
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.
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.
I'm surprised that you didn't make any mention of the IMA-18-1 solid state replacements for the 2 tubes. I've had them installed in one my SM-5228 VTVM's since the late 70's, the other I have I kept original. Still have another NOS set stashed somewhere in the lab that I've never used. I use the 5228's for alignments and have the HV probe for checking CRT anode voltages.
Excellent! Thank you!
Hi Is that a Electrolytic capacitor next to diode, Mine had a non, but someone changed them.is that wrong
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.
Great job, and much appreciated
Can I have a pdf of your cad schematic drawing? I really enjoyed your video, I just subscribed. Thank you for your effort
As I mentioned, the PDF is downloadable here: www.serpentwebsite.com/fileshare.htm
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?
Thanks alot.
thaks for the video i jave one is du not work corectly
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 found an IM-18 amongst my late fathers possessions. It doesn't mean anything to me, but I would love it to go to a good home. Would anyone be interested in it.
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.