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OT - VTVM’s are awesome


Stephen
 

A while back I fell in love with these older piece of test gears. I love them and still use them to this day. Then yesterday I had to measure several high value resistors, from 30M up to 90M. None of my DMM, whether handheld or bench could read them. It’s then that I realized that 2 of my VTVM’s were able to read up to a whooping 5000M ohm!!! I was really impressed...


Dale H. Cook
 

On 12/9/2020 10:02 AM, Stephen wrote:



A while back I fell in love with these older piece of test gears. I
love them and still
use them to this day. Then yesterday I had to measure several high
value resistors,
from 30M up to 90M. None of my DMM, whether handheld or bench could read
them. It’s then that I realized that 2 of my VTVM’s were able to
read up to a
whooping 5000M ohm!!! I was really impressed.


In recent years I have sold almost all of my VTVMs while downsizing to prepare for moving to a smaller house. I have solid state equipment that does almost everything that those VTVMs did. My DER EE DE-5000 LCR meter measures resistances up to 200 megOhms. For anything higher I still have my General Radio Type 544-BS4 Megohm Bridge. It can resolve the difference between 1,000,000 megOhms and an open circuit, has internal 150V and 500V supplies for measurement, and can be used with an external supply up to 500V.
--
Dale H. Cook, GR/HP/Tek Collector, Roanoke/Lynchburg, VA
https://plymouthcolony.net/starcity/radios/


Jean-Paul
 

Dale had built the HeathKit V-7A in 1950s..1960s, still have it with the manyual! Have to unearth and try out.

Had a 1.5V D cell for Ohms hope it did not corrode.....

Yes the GENRAD bridges are fine for megohm R, have the 1864 type megohmeters but needs a lot of work....

Also acquired some 1000M and other R (not precision) from Victoreen in an avionic HVPS project.....Memories

Big sign: DANGER 10,000 MEGOHMS"

Jon


Stephen
 

On Wed, Dec 9, 2020 at 06:24 AM, Dale H. Cook wrote:

In recent years I have sold almost all of my VTVMs while downsizing to
prepare for moving to a smaller house. I have solid state equipment that
does almost everything that those VTVMs did. My DER EE DE-5000 LCR meter
measures resistances up to 200 megOhms. For anything higher I still have
my General Radio Type 544-BS4 Megohm Bridge. It can resolve the
difference between 1,000,000 megOhms and an open circuit, has internal
150V and 500V supplies for measurement, and can be used with an external
supply up to 500V.
--
Dale H. Cook, GR/HP/Tek Collector, Roanoke/Lynchburg, VA
https://plymouthcolony.net/starcity/radios/
I have nothing against solid state stuff, I have tons of them. VOM’s and VTVM’s are just much cooler to me, and I like using them. But yes, they do take more space.


Stephen
 

On Wed, Dec 9, 2020 at 06:30 AM, Jean-Paul wrote:


Dale had built the HeathKit V-7A in 1950s..1960s, still have it with the
manyual! Have to unearth and try out.

Had a 1.5V D cell for Ohms hope it did not corrode.....

Yes the GENRAD bridges are fine for megohm R, have the 1864 type megohmeters
but needs a lot of work....

Also acquired some 1000M and other R (not precision) from Victoreen in an
avionic HVPS project.....Memories

Big sign: DANGER 10,000 MEGOHMS"

Jon
None of mine bot one has batteries it them.
The ones I use the most have 7 tubes in them + a EA52 in the HF AC probe.


Simon
 

I wanted to check leakage on a switch wafer that I had mistakenly tried to clean with switch cleaner. The wafer was bakelite/phenolic and became slightly conductive after cleaning. I could measure resistance between various contacts using my VTVM (Ferisol A206), which showed about 2-3 GΩ. I was advised to soak the wafer in a well-known oven cleaner in France (Briochin) diluted in hot water. After a soak for an hour of so, rinsing well with last rinse in deionized water, I dried it in a warm oven for a few hours and voilà could no longer measure any leakage between the pins.
Simon


Joe Laffey
 

On Wed, 9 Dec 2020, Stephen wrote:

On Wed, Dec 9, 2020 at 06:30 AM, Jean-Paul wrote:

None of mine bot one has batteries it them.
The ones I use the most have 7 tubes in them + a EA52 in the HF AC probe.
In my Eico with the 7-inch meter face I installed a little LM317 circuit to the battery source. No worries about battery replacement/leakgae.

No change in accuracy or noise to be seen anywhere either.

--
73
Joe Laffey


Stephen
 

On Wed, Dec 9, 2020 at 06:59 AM, Joe Laffey wrote:


On Wed, 9 Dec 2020, Stephen wrote:

On Wed, Dec 9, 2020 at 06:30 AM, Jean-Paul wrote:

None of mine bot one has batteries it them.
The ones I use the most have 7 tubes in them + a EA52 in the HF AC probe.
In my Eico with the 7-inch meter face I installed a little LM317 circuit
to the battery source. No worries about battery replacement/leakgae.

No change in accuracy or noise to be seen anywhere either.

--
73
Joe Laffey
It’s a good thing. I may do that on the one that does use a battery.


Stephen
 

On Wed, Dec 9, 2020 at 06:58 AM, Simon wrote:


I wanted to check leakage on a switch wafer that I had mistakenly tried to
clean with switch cleaner. The wafer was bakelite/phenolic and became slightly
conductive after cleaning. I could measure resistance between various contacts
using my VTVM (Ferisol A206), which showed about 2-3 GΩ. I was advised to
soak the wafer in a well-known oven cleaner in France (Briochin) diluted in
hot water. After a soak for an hour of so, rinsing well with last rinse in
deionized water, I dried it in a warm oven for a few hours and voilà could no
longer measure any leakage between the pins.
Simon
Good tip!! Thanks.
I have a Ferisol A204, but the galvanometer is dead.
The 2 VTVM’s I’m talking about are METRIX 745’s.

https://groups.io/g/TekScopes/album?id=257707


Stephen
 

On Wed, Dec 9, 2020 at 06:59 AM, Joe Laffey wrote:


On Wed, 9 Dec 2020, Stephen wrote:

On Wed, Dec 9, 2020 at 06:30 AM, Jean-Paul wrote:

None of mine bot one has batteries it them.
The ones I use the most have 7 tubes in them + a EA52 in the HF AC probe.
In my Eico with the 7-inch meter face I installed a little LM317 circuit
to the battery source. No worries about battery replacement/leakgae.

No change in accuracy or noise to be seen anywhere either.

--
73
Joe Laffey
This one has a 15cm diagonal meter.


J. L. Trantham
 

I, too, love my VTVM's but, in defense of DMM's, the Fluke 8050A can measure Conductance down to .01 nS equivalent to resistance up to 100 Gigaohm.

Haven't had a need to measure that high (or low, depending on your point of view) so far though.

Joe

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Stephen
Sent: Wednesday, December 09, 2020 9:03 AM
To: TekScopes@groups.io
Subject: [TekScopes] OT - VTVM’s are awesome

A while back I fell in love with these older piece of test gears. I love them and still use them to this day. Then yesterday I had to measure several high value resistors, from 30M up to 90M. None of my DMM, whether handheld or bench could read them. It’s then that I realized that 2 of my VTVM’s were able to read up to a whooping 5000M ohm!!! I was really impressed...


Jean-Paul
 

Hello again now I recall the battery substitute in these VTVMs.

Heathkit V7a used a 12AX7 in the bridge and a dual diode 6AL5 for AC rectification.
the 7" meter movement had mirror scales, a Really fine hobbyists instrument for 20-25$ circa 1960.

http://www.w6ze.org/Heathkit/Heathkit_019_V7a.pdf

In 1970s HP made a solid state 410c series that had VTVM functions, have to check my archive for the manual and perhaps even the meter......

It will be interesting to find them and after decades in deep storage, to see are they still working? How bad (or good) is calibration ?

Jon


Stephen
 

On Wed, Dec 9, 2020 at 07:35 AM, J. L. Trantham wrote:


I, too, love my VTVM's but, in defense of DMM's, the Fluke 8050A can measure
Conductance down to .01 nS equivalent to resistance up to 100 Gigaohm.

Haven't had a need to measure that high (or low, depending on your point of
view) so far though.

Joe
I agree, higher end DMM are very good too. But I don’t know, these just have that cool factor about them.


Simon
 

I have a Metrix 745 which has an innovative DC regulation circuit and only requires one calibration step, but it is fairly big. I like the Ferisol which has automatic polarity detection. Pity about the Ferisol A204. I have the earlier A201, which works quite well and also has the EA52 AC probe. I think they were inspired by the HP410B an eminent precursor.
Simon


snapdiode
 

It's unbelievable but in the '90s they still had a VTVM at my school...


Brenda
 

I have 3 Heathkit IM-28 VTVMs that I love using, just because they have that cool factor, plus it seems like they are quicker to respond to changes in voltage compared to a DMM. All 3 of mine had to have all of it's precision resistors replaced as they were way way out of tolerance! But all 3 are very accurate enough to make me happy to use. They still have to battery but thanks to another member on here, I think I will be installing a LM317 circuit to eliminate the batteries. I have found that the VTVM's are great for checking pots while rotating the shaft. Any slight scratchiness, the VTVM was very quick to respond. I also have a Heatkit IM-18, but I am at a loss with it so I will have to look at it another time. I should also note that I use them for monitoring the power supplies on my tube type Tektronix scopes to keep an eye out for those capacitors!


Stephen
 

On Wed, Dec 9, 2020 at 07:57 AM, Simon wrote:


I have a Metrix 745 which has an innovative DC regulation circuit and only
requires one calibration step, but it is fairly big. I like the Ferisol which
has automatic polarity detection. Pity about the Ferisol A204. I have the
earlier A201, which works quite well and also has the EA52 AC probe. I think
they were inspired by the HP410B an eminent precursor.
Simon
Yes the A204 is a military version. This one has the « Marine Nationale » logo on it.
Yes, the 745 is quite big, and weighs 9Kg too. I don’t recall the One-Step DC calibration at all... are you sure about that?


Stephen
 

On Wed, Dec 9, 2020 at 08:18 AM, Brenda wrote:


I have 3 Heathkit IM-28 VTVMs that I love using, just because they have that
cool factor, plus it seems like they are quicker to respond to changes in
voltage compared to a DMM. All 3 of mine had to have all of it's precision
resistors replaced as they were way way out of tolerance! But all 3 are very
accurate enough to make me happy to use. They still have to battery but thanks
to another member on here, I think I will be installing a LM317 circuit to
eliminate the batteries. I have found that the VTVM's are great for checking
pots while rotating the shaft. Any slight scratchiness, the VTVM was very
quick to respond. I also have a Heatkit IM-18, but I am at a loss with it so I
will have to look at it another time. I should also note that I use them for
monitoring the power supplies on my tube type Tektronix scopes to keep an eye
out for those capacitors!
I also had to replace lots of resistors that where completely out of tolerance.
But now these things are very accurate and as precise as I’ll ever need.
I agree, they do respond much quicker than any DMM I’ve used.
I don’t know, I just love the needles I guess...


Jean-Paul
 

Hi: The Heathkit, Eico, Paco and Knight (Allied) VTVMs all had bannana jacks and probe cables of rubber, that cracked over the years. I recall one meter with the old microphone screw coax perhaps for AC input shield.

The VT bridge circuit seems to limit meter movement (200 uA?) overload, I never had damage to the movements even with extreme overload.

IM-28 were the newer series but basically same as the VT-7.

Hope that someone can please post a link to the Zener or LM317 battery substitue circuit?

Jon


Stephen
 

On Wed, Dec 9, 2020 at 09:47 AM, Jean-Paul wrote:


Hi: The Heathkit, Eico, Paco and Knight (Allied) VTVMs all had bannana jacks
and probe cables of rubber, that cracked over the years. I recall one meter
with the old microphone screw coax perhaps for AC input shield.

The VT bridge circuit seems to limit meter movement (200 uA?) overload, I
never had damage to the movements even with extreme overload.

IM-28 were the newer series but basically same as the VT-7.

Hope that someone can please post a link to the Zener or LM317 battery
substitue circuit?

Jon
Out of my 6 VTVM’s only 1 uses batteries for resistance reading.
But here’s a link I found. Hope this helps.
https://youtu.be/IlaGhx2rqK8