Hi,
Looking for my first VTVM and want to use vintage. What is the story on the HeathKit V-7A?

i have one but have never used it, so i can't tell you much about it.

Hi,
I'm looking for one maybe?

if you are interested, here is a nice one:

viewtopic.php?f=15&t=187431

Hi ,
Thanks,but why has 150 people looked at this and no one has bought it??? Like I said I'm new at this!

not a lot of people need something like that as most probably have one or two already.

personally, i've not found a need for the one i have.

Hi,
Well I told the man I wanted it. Well see. It looks like it has a DC probe but no leads. Do you know what leads it needs? Thanks!

just the regular test leads that you'd use with any common meter.

The V7-A needs 3 test leads-

Banana plug to alligator clip black Common
Banana plug to test probe red AC volts and Ohms
Phone plug , shielded cable, test probe with 1 meg resistor connected in series just before tip DC volts.

If the V7-A works properly , it works very well.

Nice VTVM, you did good. It's a plus that it comes with an original manual (in excellent condition, too); that'll help you maintain it. I've got an IM-11, which is the same circuit in an updated mechanical layout.

The one in the ad does look like a very nice one and is from a responsible owner.
A big problem with buying some of that stuff from people that just picked it up at an estate sale to sell on eBay is big time battery corrosion!
Add NO rust on the cabinet and NO cracks in the meter face cover and it is worth it to pay a bit more in my opinion.
The V-7 is easy to work on and you can find schematics etc. easily.
I have one I rescued from an estate sale. It had a leaky battery in it for years but it cleaned up nicely with some work and works ok.

Hi,
Thanks Gentlemen,looks like I'm the proud owner of a HK V-7A! I thought it was pretty good deal as the cap(s) have been replaced and it has been gone over by the gentleman and actually used. Should be good to go and comes with the original manual and the DC probe! Thanks again!

Good news! The DC meter function will take you through any voltage issue in a tube radio.

And don't measure how many ohms there are in the live 120 volt line .

If you do, you'll need to replace the 9.1 ohm precision resistor. (Wonder how many V7A
owners know that )

This is a typical "two tube" VTVM. They were made by the millions by a number of different companies, all basically the same. A dual triode like a 12AU7 is used as a differential DC amplifier, and a diode like a 6AL5 is used as a rectifier for measuring AC voltages. What's really nice about the V-7A is that it does not use any special probes or oddball connectors. The manual will show you how to assemble the AC volts/Ohms probe and ground clip, which can be made of common, readily available parts.

There are two big advantages to a VTVM that you will not find on other meters. One is that the input impedance is very high, 10 megohms on DC and somewhat less on AC. This allows you to take measurements in tube circuits, which are also often high impedance themselves, without loading the circuits down and causing false readings. Even the finest, most sensitive analog VOM can get into trouble this way in some situations. Digital multimeters vary all over the lot. Some of the better ones do have 10-megohm input impedances, but the more down-to-earth, garden variety ones are in the 1-megohm range. Somewhere in the middle between VOMs and VTVMs.

The other point in favor of a VTVM like the V-7A is that it can be used at RF frequencies, up to about 3 MHz or so in this case. It will actually indicate higher frequencies, but at reduced sensitivity. This can be handy for troubleshooting oscillator and IF problems. Neither VOMs nor standard handheld DMMs can do this. (There are some high end bench model DMMs that can measure RF with ease, but they are usually lab instruments that are out of the running price-wise).

Hi,
Thanks Gentlemen,I'm now looking at making up a set of vintage leads (with new wire and plugs of course) that will match the DC probe! I'm going to a small Vintage Radio swap meet tomorrow and may get lucky. I want my stuff to look correct as well as work correctly and do not ffeel that going to Radio Shack and buying a $6.00 pair of leads is right!

If this is a meter you intend to use, don't knock the modern stuff. Old, used test leads such as you might be tempted to buy off a hamfest table often suffer from cracking or deteriorated rubber insulation and general wear and tear. I'd rather trust my ticker to new, good quality plastic insulation, thank you! But since the probes simply plug into the meter on a 1/4" phone jack, there is nothing stopping you from making a "vintage" set for show, and a "modern" set to use.

I have modified my V-7A (and my IM-11 and my IM-18).

The modification of the IM-11 where the 1 meg resistor is placed inside the instrument will make
radio circuit testing difficult as DC measurements will be subject to circuit disturbance. i.e. Measuring the
negative voltage on the first grid of a pentagrid converter will cause detuning on AM and on short wave
cable capacitance could shut down the oscillator.

So it looks like you've moved the 1-meg resistor from the DC probe inside the instrument and isolated all the circuitry from chassis ground. Seems like a lot of work to turn three VTVM into battery testers, but that's what you've got because they are not good for much more than that now.

Note to OP: One other big difference between VTVMs of this type and other kinds of meters is the ground clip and circuit ground are (normally) connected to the chassis and case. This provides superior RF sheilding and stability, but it means that a VTVM should never be used for measuring AC line voltages. If you want to measure the AC line, use a plastic-cased DMM that is fused and rated for the purpose, or a plastic VOM.

The 1-meg resistor is in the probe to isolate the circuit you are testing from the capacitance of the coax cable which connects the probe to the meter. The resistor should be left in the probe, otherwise some of the functionality of the VTVM is lost.

Hi Gentlemen thanks for the heads up! At this time I'm just trying to learn to walk and the varsity techniques will have to wait!

On the vintage leads,what I intended to convey but failed in is that I want to build the leads with new test cord wire with new banana plugs but want to use the vintage hard shiney plastic probes that match the DC probe that is all ready there! This is maybe anal but that's the way I want to keep equipment and I then feel pride of ownership I guess as I use it!