FA: Simpson 303 VTVM oldie but goodie!!!
Dave Edwards
Karl
> http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7578034133&rd=1&sspagename=STRK%3AMESE%3AIT&rd=1
I keep seeing the term "VTVM", but what is so special about them? What
is better about them than my cheap little Radio Shack multimeter?
Bill Turner
Tube Volt Meter, as opposed to a plain analog meter with no active
components.
In today's world, about the only advantage they would have is immunity
to massive voltage overloads that would smoke a solid state device.
I'll bet if you accidentally touched the anode lead of a CRT with your
solid state meter it would be history. A VTVM would most likely
survive.
Mostly though, is the nostalgia. I used one for twenty years doing TV
repair back in the tube days. It did the job, but I have to admit my
everyday meter now is a Fluke 87. Sigh.
Bill T.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
ORIGINAL MESSAGE:
Phil Allison
"Karl"
>
> I keep seeing the term "VTVM", but what is so special about them? What
> is better about them than my cheap little Radio Shack multimeter?
>
** If that Radio Shack meter is a reasonable digital one - then not a great
deal.
If a cheap analogue type - then a good VTVM eats it alive.
Egs .
10 megohms input impedance on all AC and DC volts ranges.
Wide AC frequency response.
Pretty much accidental abuse proof ( aside from a big drop).
The big meter looks very cool compared to an LCD display.
One drawback is that readings are ground referenced as with a scope.
......... Phil
Pooh Bear
Karl wrote:
The warm fuzzy feeling they give you. A modern DVM will be loads more accurate.
Graham
Uncle Peter
"Pooh Bear" <rabbitsfriend...@hotmail.com> wrote in message
news:43BF8B8E...@hotmail.com...
>
>
> Karl wrote:
>
> The warm fuzzy feeling they give you. A modern DVM will be loads more
accurate.
>
> Graham
>
For a lot of vintage tube related repairs, you don't need accuracy or
precision, but
the analog meter is a lot easier to follow when doing alignment, etc.
Pete
Uncle Peter
"Bill Turner" <no...@nohow.com> wrote in message
news:egmur1hse21ean9fg...@4ax.com...
> In today's world, about the only advantage they would have is immunity
> to massive voltage overloads that would smoke a solid state device.
> I'll bet if you accidentally touched the anode lead of a CRT with your
> solid state meter it would be history. A VTVM would most likely
> survive.
>
> > Bill T.
>
Unless you have a Heath VTVM that used a 6AL5 for the AC
rectifier in the metering circuit. Getting across the secondary
of a modest receiver's power transformer usually arced the
6AL5, taking the meter movement along with it. Heath replaced
those associated parts at least two times in my kit before I
swore off using it for AC measurements.
Pete
ws
Actually, that isn't quite true. The impedance of a "cheap little Radio
Shack multimeter" is likely to be very low - in the order of <100K
A VTVM is likely to have an impedance >10Megs and if you're measuring
100V across 1Meg, inserting a 100K impedance into the circuit *is* going
to give you problems!
http://www.elexp.com/t_load.htm
I agree that impedance and absolute accuracy may be better in a good
DVM, but sometimes a VTVM is very useful. Do see this article for an
explanation:
http://www.tone-lizard.com/VTVM.htm
Cheers,
WS
Pooh Bear
ws wrote:
> Pooh Bear wrote:
> >
> > Karl wrote:
> >
> >
> >>Dave Edwards wrote:
> >>
> >>>http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7578034133&rd=1&sspagename=STRK%3AMESE%3AIT&rd=1
> >>
> >>I keep seeing the term "VTVM", but what is so special about them? What
> >>is better about them than my cheap little Radio Shack multimeter?
> >
> >
> > The warm fuzzy feeling they give you. A modern DVM will be loads more accurate.
> >
>
> Actually, that isn't quite true. The impedance of a "cheap little Radio
> Shack multimeter" is likely to be very low - in the order of <100K
What makes you say that ?
Graham
Adam Stouffer
> They are from the days before transistors. "VTVM" stands for Vacuum
> Tube Volt Meter, as opposed to a plain analog meter with no active
> components.
>
> In today's world, about the only advantage they would have is immunity
> to massive voltage overloads that would smoke a solid state device.
> I'll bet if you accidentally touched the anode lead of a CRT with your
> solid state meter it would be history. A VTVM would most likely
> survive.
>
Most fluke meters survive pretty well. I've burned out a 1k fuse
resistor twice now from accidental overloads. The latest was from
touching the plate lead and getting a nice purple RF arc. Tought that
killed it for sure.
Adam
ws
OK, to clarify, I was comparing apples to apples (i.e. analog). The
specs for a currently available model is here:
http://www.radioshack.com/product/index.jsp?parentPage=search&cp=&productId=2103170&kw=multimeter&tab=techSpecs
While cheap DVMs have higher input impedance, they aren't quite up to
VTVM standards. The cheap DVM that they list for $19.99 only has an
impedance of 1Meg, which is still low enough to affect readings in
certain cases.
http://rsk.imageg.net/graphics/uc/rsk/Support/ProductManuals/2200810_PM_EN.pdf
Only the $25.99 and the $49.99 models are 10Meg.
The point here is that it's not purely "warm fuzzies", but that each
tool, including the VTVM has it's place, and it's limitations, as shown
in the links you snipped.
Regards,
WS
Sander deWaal
>While cheap DVMs have higher input impedance, they aren't quite up to
>VTVM standards. The cheap DVM that they list for $19.99 only has an
>impedance of 1Meg, which is still low enough to affect readings in
>certain cases.
Not only that, the frequency range of said cheap DMMs is usually very
limited (up to 400 Hz I believe).
My various Fluke meters aren't much better, BTW.
--
"Audio as a serious hobby is going down the tubes."
- Howard Ferstler, 25/4/2005
Don Pearce
wrote:
>ws <a@b.c> said:
>
>>While cheap DVMs have higher input impedance, they aren't quite up to
>>VTVM standards. The cheap DVM that they list for $19.99 only has an
>>impedance of 1Meg, which is still low enough to affect readings in
>>certain cases.
>
>
>Not only that, the frequency range of said cheap DMMs is usually very
>limited (up to 400 Hz I believe).
>
>My various Fluke meters aren't much better, BTW.
My Fluke, with built-in scope function, goes to many tens of kHz very
comfortably.
d
Pearce Consulting
http://www.pearce.uk.com
Pooh Bear
ws wrote:
> Pooh Bear wrote:
> >
> > ws wrote:
> >
> >
> >>Pooh Bear wrote:
> >>
> >>>Karl wrote:
> >>>
> >>>
> >>>
> >>>>Dave Edwards wrote:
> >>>>
> >>>>
> >>>>>http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=7578034133&rd=1&sspagename=STRK%3AMESE%3AIT&rd=1
> >>>>
> >>>>I keep seeing the term "VTVM", but what is so special about them? What
> >>>>is better about them than my cheap little Radio Shack multimeter?
> >>>
> >>>
> >>>The warm fuzzy feeling they give you. A modern DVM will be loads more accurate.
> >>>
> >>
> >>Actually, that isn't quite true. The impedance of a "cheap little Radio
> >>Shack multimeter" is likely to be very low - in the order of <100K
> >
> >
> > What makes you say that ?
> >
>
> OK, to clarify, I was comparing apples to apples (i.e. analog). The
> specs for a currently available model is here:
> http://www.radioshack.com/product/index.jsp?parentPage=search&cp=&productId=2103170&kw=multimeter&tab=techSpecs
>
That's *not* a DVM of course ! Nor especially cheap.You have to pay quite a lot for moving coil meters. I did
wonder if that was what you meant.
> While cheap DVMs have higher input impedance, they aren't quite up to
> VTVM standards. The cheap DVM that they list for $19.99 only has an
> impedance of 1Meg, which is still low enough to affect readings in
> certain cases.
> http://rsk.imageg.net/graphics/uc/rsk/Support/ProductManuals/2200810_PM_EN.pdf
>
> Only the $25.99 and the $49.99 models are 10Meg.
They are still hardly expensive !
> The point here is that it's not purely "warm fuzzies", but that each
> tool, including the VTVM has it's place, and it's limitations, as shown
> in the links you snipped.
The error simply reading the needle on a VTVM will exceed the measurement error on most DVMs.
Graham
Pooh Bear
Uncle Peter wrote:
That is indeed where they score.
Graham
Michael A. Terrell
Most of the VTVMs i have owned had either a separate probe for DC
measurements, or a switch to select AC/ohms or DC. They had a 1 megohm
resistor at the probe to keep from loading down a tuned circuit, or
stopping an RF oscillator, which would change the voltage. They are
still handy when looking for oscillator problems on PC boards.
--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.
Michael A. Terrell
Central Florida
Scott Dorsey
>
>I keep seeing the term "VTVM", but what is so special about them? What
>is better about them than my cheap little Radio Shack multimeter?
Well, it has a much higher input impedance than a cheap Radio Shack
analogue meter, and it also has a probe for reading RF.
The RF probe combined with the high input Z makes it very handy for
peaking coils and similar operations which are next to impossible to
do with a digital meter. You can't see trends easily on the digital
meter.
A modern FET-input analogue meter with an RF probe will do just as well
as an old VTVM, and it'll be more stable too. But you won't find one
at the hamfest for five bucks like you will a good VTVM.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Sander deWaal
>>Not only that, the frequency range of said cheap DMMs is usually very
>>limited (up to 400 Hz I believe).
>>My various Fluke meters aren't much better, BTW.
>My Fluke, with built-in scope function, goes to many tens of kHz very
>comfortably.
A scopemeter, well, duh! :-)
I have a Fluke 12, a 73 and an old 8000-something, and they won't do
anything accurate above 1 kHz.
Don Pearce
wrote:
>don...@pearce.uk.com (Don Pearce) said:
>
>>>Not only that, the frequency range of said cheap DMMs is usually very
>>>limited (up to 400 Hz I believe).
>
>>>My various Fluke meters aren't much better, BTW.
>
>>My Fluke, with built-in scope function, goes to many tens of kHz very
>>comfortably.
>
>
>A scopemeter, well, duh! :-)
>
>I have a Fluke 12, a 73 and an old 8000-something, and they won't do
>anything accurate above 1 kHz.
Mine is an 867B. Just read the spec, and it is good for 300kHz full
RMS. It is also just about bomb-proof as far as I can tell. One nice
feature is that it also gives a pretty good imitation of an analogue
display.
- exray -
>
>>the analog meter is a lot easier to follow when doing alignment, etc.
>>
>>Pete
>
>
> That is indeed where they score.
>
> Graham
I suppose. I haven't used my old VTVM for alignment in so many years I
have forgotten! I think much of that argument has been dispelled in
recent years with DMMs that update and refresh the display faster than
the wink of an eye. I remember the early DMMs that weren't worth a crap
for alignment even with the little 'bar'... that had poor resolution.
Biggest DMM plus for me is that I can set the meter right alongside the
chassis and glance over and see it rather than looking up on the shelf.
And I can actually see the big 1 inch numbers without squinting my
tired old eyes on an old faded 'red' scale :)
-ex
Brenda Ann
"Sander deWaal" <nos...@wanadoo.nl> wrote in message
news:f9b0s1lkhv3c3k5rf...@4ax.com...
Fluke 97 is good to 50MHz.. though I wouldn't say it's resolution gives a
very true waveform image.
BFoelsch
ago...
The standard VTVM circuit has an impedance of 10M in the meter and 1M right
at the tip of the probe (on the DC ranges, the AC ranges are direct
connections). That means that the capacitance of the cable and the input
capacitance of the meter is virtually isolated from the circuit under test.
Using a standard VOM, of any impedance, to measure the DC grid voltage of a
tube local oscillator is generally fruitless because the added capacitance
of the cable and meter, sometimes 100 pF or more, loads the oscillator and
either stops it or badly detunes it. The VTVM however has only a very few pF
at the tip (on the DC ranges) and provides only minimal circuit disturbance.
That is why VTVMs either have separate AC and DC probes or a probe with a
switch. I get a kick out of the experts who modify their Heath VTVMs to work
without a switchable probe. This completely defeats the only real remaining
benefit of a VTVM!
Now, if someone designs a DVM with a 1 M resistor in its probe to accomplish
the same result, we can officially announce the death of the VTVM. Of
course, using an oscilloscope with a 10X probe accomplishes exactly the same
thing.
"- exray -" <ex...@coqui.net> wrote in message
news:11s0e02...@corp.supernews.com...
- exray -
>
> Now, if someone designs a DVM with a 1 M resistor in its probe to accomplish
> the same result, we can officially announce the death of the VTVM.
I just twist a resistor around the end of the DMM probe if I see there
is a problem.
-Bill
Uncle Peter
Yeah, well you offset most VTVMs for a zero center reading for aligning
FM discriminators!! So there! Do that with your fancy DVM! HAR!
--Pete
- exray -
>
> Yeah, well you offset most VTVMs for a zero center reading for aligning
> FM discriminators!! So there! Do that with your fancy DVM! HAR!
>
> --Pete
No need to offset. I can recognize the digit 'zero' and a little minus
sign pops up when I cross it. Harhar!!
-Bill
Michael A. Terrell
>
> Nobody has mentioned the MAIN reason VTVMs were preferred for radios years
> ago...
Really? I thought I explained it in my reply.
Tonni
For the warious reasons mentioned i simply use all my meters
occationly.... - Also more at the same time. :-D
And, amongst others, that's:
ANTON TS505D/U VTMM, with 500Mc's calibrated diode-probe....
AVO Mk. 8
BRUNO ME-70C/PSM-6B multimeter with dc-z = 1Kohm/V or 20Kohm/V :-)
Brüel & Kjaer 2401 mV VTM
Grundig MV20 mV VTM
HP 4½ digit. 34702A Bench DVOM
Metex 3800 DMM
- They ALL work FLAWLESSLY, and i wouldn't part with any of them!!!
Best regards
Tonni, Denmark
Keep the glow up!
Pooh Bear
Tonni wrote:
You must have a lot of spare bench space !
Graham
Tonni
"Pooh Bear" <rabbitsfriend...@hotmail.com> skrev i en meddelelse
news:43C0D2CC...@hotmail.com...
> You must have a lot of spare bench space !
>
> Graham
>
And some shelve's!!! :-D
Best regards
Tonni
Keep the glow up!
BFoelsch
"Tonni" <ha...@hardware.dk> wrote in message
news:43c0c88d$0$200$edfa...@dread11.news.tele.dk...
I agree in principle. I have a list of meters much longer than yours, but I
really use only three, a B&K 5492A, an HP???? AC Voltmeter, and a Fluke 87
handheld. I have a couple nice scopes with readouts and math so I use those
as meters for some applications, like measuring RF voltages, or calculating
phase angle or power. I really like the B&K 5492A, it replaced a whole shelf
full of single purpose meters, but it has a dual display so you can measure
two parameters at once.
The problem I have with test equipment is space on the bench. I have all
kinds of stuff in storage, but it really boils down to using the instrument
that puts the greatest versatility in the smallest space. Once in a while I
need to do lots of simultaneous measurements and drag out lots of stuff, but
that is rare.
Patrick Turner
BFoelsch wrote:
> Nobody has mentioned the MAIN reason VTVMs were preferred for radios years
> ago...
>
> The standard VTVM circuit has an impedance of 10M in the meter and 1M right
> at the tip of the probe (on the DC ranges, the AC ranges are direct
> connections). That means that the capacitance of the cable and the input
> capacitance of the meter is virtually isolated from the circuit under test.
>
> Using a standard VOM, of any impedance, to measure the DC grid voltage of a
> tube local oscillator is generally fruitless because the added capacitance
> of the cable and meter, sometimes 100 pF or more, loads the oscillator and
> either stops it or badly detunes it. The VTVM however has only a very few pF
> at the tip (on the DC ranges) and provides only minimal circuit disturbance.
> That is why VTVMs either have separate AC and DC probes or a probe with a
> switch. I get a kick out of the experts who modify their Heath VTVMs to work
> without a switchable probe. This completely defeats the only real remaining
> benefit of a VTVM!
>
> Now, if someone designs a DVM with a 1 M resistor in its probe to accomplish
> the same result, we can officially announce the death of the VTVM. Of
> course, using an oscilloscope with a 10X probe accomplishes exactly the same
> thing.
I have a probe which uses 1M to 10k R divider which reduces the voltage
100 times and causes little problem with most AM radio circuits,
and the stray C is low.
So if you have 10V DC to measure, it comes to the meter/CRO at 0.1V.
Or if V = 1000V, 10V is at the meter or CRO.
Where 1000V is involved, the I flow is only 1mA, which usually
won't upset too many things you may test in tubed gear.
I have the R divider with 3 x 330k in series then the 10k , and mounted on a
300mm
peice of wooden dowel with generous multi layer heatshrink to prevent
stray unwanted contact when the small hook probe end is being
hooked around a circuit.
Its nice to see the IF envelope of an IF stage without losses, or the
detector envelope etc.
Many voltages in RF or IF stage outputs is quite high, maybe 100Vrms of signal
at the 455 kHz IF, so its easily read after reducing 100 times in level.
The output from the 10k is OK for most CRO at relatively low RF.
But for better measuring, mounting a tube cathode follower in a can with
umbilical cable and screened lead from the cathode and bootstrapped grid bias
gices a nice rugged
high impedance low capacitance probe that reduces the input voltage only a dB or
so.
A 6J6 may be quite good, EC97, etc.
Maybe a 6DJ8, 12AT7 also.
But input voltage is limited to the
max Vo of the CF, maybe only 40Vrms.
The grid input to the follower must have a DC blocker cap
to stop the probe affecting DC bias voltages in grid circuits.
If such a probe with a 200V supply and idle V at the CF cathode is say 100V,
then connecting to a bias voltage of -40V will make the CF cut right off.
But such a proble won't mind occasional overloads that would
blow the crap out of a j-fet.
Patrick Turner.
My millivolt ac meter I made has Vin limiting, fet input, all SS amplifying
and a 1metre shielded cable doesn't do much to most signals.
R in is 500k on the lowest range of 0-10 mV, but much
higher R in when measuring up to 1,000V.
Bandwidth is 2Hz to 2MHz, and some C compensation across the
Rin switched dividers is required to flatten response.
For measuring smallish signal voltages to 30MHz
I have a wide band amp with two RF transistors that gives 26dB of gain,
50 ohms termination output impedance, and which is in the millvolt meter.
I have a couple of partially stuffed/burned VTVM laying around that I was given,
but I doubt i will bother to repair them.
Patrick Turner.
gb
news:gnPvf.40382$Mi5.33533@dukeread07...
>
> "Pooh Bear" <rabbitsfriend...@hotmail.com> wrote in message
> news:43BF8B8E...@hotmail.com...
>>
>>
>> Karl wrote:
> > The warm fuzzy feeling they give you. A modern DVM will be loads more
> accurate.
>>
>> Graham
>>
>
> For a lot of vintage tube related repairs, you don't need accuracy or
> precision, but
>
> Pete
>
analog meter). Yes, I have the Fluke 87 also and use it for most routine
bench measurements .. but the Heath is used for alignments and when I want
an analog movement to see what is really going on ...... about same reasons
some good troubleshooters still keep analog scopes.
Greg
Pooh Bear
gb wrote:
No substitute for a good analog scope !
Tek 465 here.
Graham
Tonni
>
> No substitute for a good analog scope !
>
> Tek 465 here.
>
> Graham
Halleluja!!!
Tek 547 Here! And D..m, it's good!
/Tonni
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Dana
Ron in Radio Heaven
Dana <da...@panix.com> wrote in message
news:Pine.NEB.4.63.06...@panix1.panix.com...
> I have 1 in the Griffin, Georgia area for sale.
>
Do you think you could tell us a little about it?
Condition, manufacture, model, etc...
Ron
Dana
n4pge