Latest project Transistor VTVM build

[SmithDoor]

My wife said I need a indoor hobby.
So I designed and built a transistor vacuum tube voltmeter.
Here is a photo of finished vtvm and schematic.

Dave

PS: The probes was machined

 

[lee webster]

The last time I messed about with electronics was pre 1968. I remember buying valves, tubes, for something, and transisters, resistors etc for other projects. I sometimes think I should have stuck with electronics rather than become a carpenter.

 

[SmithDoor]

The last time I messed about with electronics was pre 1968. I remember buying valves, tubes, for something, and transisters, resistors etc for other projects. I sometimes think I should have stuck with electronics rather than become a carpenter.

Electronics in 1970's switch to the chips. TV repair when down and alot fewer jobs electronic jobs. Electronics was my dream job too. In high school and college I work as iron worker/welder and machinist. It made lot more money than tv repair.

Dave

 

[GreenTwin]

When I started in college, the oscilloscopes in the labs were all tube-type, the labs were full of analog computers, and there was a punch card IBM mainframe with line printer that ran FORTRAN.

I recall looking at the analog computer, and asking "What is it ? and how does it work ?".
I was shocked to find out that basically any system can be modeled/simulated using resistors, capacitors, and inductors.
I thought there must be more components required, but three is all there is.

Photo from the link below.

http://ferretronix.com/march/analog_computers/
The analog computers we used actually had a large number of dials on them, for adjusting the values of the components, but we did have the spaghetti wiring.

Electronics of 1976 were not that sophisticated, but that was changing fast, and I sidestepped electronics design and went into medium voltage power distribution design.
Luckily medium voltage power distribution is somewhat of a static discipline, and the 3-phase systems have not changed much at all from the time it was popularized by Westinghouse in the early 1900's.

Power breakers are now chocked full of electronic relays, and one has to be very familiar with how they work, and to some extent how they are programmed and applied.

I miss the days when you could open the back of a TV set (carefully avoiding the often fatal large capacitor), and look at a handful of tubes which ran the entire TV.

Diddo for pinball machines.
Banks and banks of solenoid-operated mechanical contacts, and no electronics at all.

I really miss the pre-electronics era, where things were simple, and almost anyone could learn to build and/or repair anything.
Electronic kits were abundant from Radio Shack, and who did not have their own crystal radio?

 

[SmithDoor]

When I started in college, the oscilloscopes in the labs were all tube-type, the labs were full of analog computers, and there was a punch card IBM mainframe with line printer that ran FORTRAN.

I recall looking at the analog computer, and asking "What is it ? and how does it work ?".
I was shocked to find out that basically any system can be modeled/simulated using resistors, capacitors, and inductors.
I thought there must be more components required, but three is all there is.

Photo from the link below.

http://ferretronix.com/march/analog_computers/
The analog computers we used actually had a large number of dials on them, for adjusting the values of the components, but we did have the spaghetti wiring.

Electronics of 1976 were not that sophisticated, but that was changing fast, and I sidestepped electronics design and went into medium voltage power distribution design.
Luckily medium voltage power distribution is somewhat of a static discipline, and the 3-phase systems have not changed much at all from the time it was popularized by Westinghouse in the early 1900's.

Power breakers are now chocked full of electronic relays, and one has to be very familiar with how they work, and to some extent how they are programmed and applied.

I miss the days when you could open the back of a TV set (carefully avoiding the often fatal large capacitor), and look at a handful of tubes which ran the entire TV.

Diddo for pinball machines.
Banks and banks of solenoid-operated mechanical contacts, and no electronics at all.

I really miss the pre-electronics era, where things were simple, and almost anyone could learn to build and/or repair anything.
Electronic kits were abundant from Radio Shack, and who did not have their own crystal radio?


View attachment 147505

Looks like a fun project.
Does it still works?

Dave

 

[SmithDoor]

FYI
The advantage of a VTVM is the amount power it takes from the circuit. This one is the most common 11 Meg aka 11,000,000 ohms per volt.

Most manufacturers built in 1960's 10 Meg to 11 Meg ohms per volts. You see in the 1950's 5 Meg to 60 Meg ohms per volt by. The 60 Meg was only in lab work.

Here is breakdown the amount of power need for measurement of the voltage.

Low cost VOM 5,000 ohms per volt
Most VOM today is 20,000 ohms per volt. Great for just ever use.

They did build 100,000 per volt VOM's work for tuning radios not best.

Oscilloscope is 1,000,000 ohms per volt. I use this for tuning radios in 1960's.

The VTVM you would at 5,000,000 ohms per volt in 1940's work great for tuning radios

1950's a lot of VTVM's from 10,000,000 to 20,000,000 ohms to volts. Great for TV tuning.

After 1960 most was 10,000,000 to 11,000,000 ohms per volt. This great almost all tuning and repair work.

The advantage of VTVM over a digital in radio tuning is you watch a the needle for max reading. The digital uses numbers.
Depending how good eyes are can very little movement of needle for max tuning position.
In 0.5 volt range this is with real good eyes 0.001 volts most can read down to 0.0025 volts.

Today you have goto used market to buy a VTVM .
You can not even find a kit today.

Dave

 

[ChazzC]

I built a HeathKit IM-28 VTVM when they were still selling them: in addition to the performance, I liked the form factor better than other VTVM’s.

My HeathKit Bench DVM is 10M/V and has a mini analog display (think s-meter size) but when I want a meter that can be set to 0 center I use my B&K FETVM.

 

[BaronJ]

Hi Guys,

One of the problems with Valve volt meters is that they can tell you lies !

I get several volts AC just from leaving the wires loose on the bench ! Now I do know where that voltage comes from and its the local FM radio station.

The point I am trying to make is that you can get deceptive voltage readings that have absolutely nothing to do with the circuit you are measuring.

 

[SmithDoor]

I built a HeathKit IM-28 VTVM when they were still selling them: in addition to the performance, I liked the form factor better than other VTVM’s.

View attachment 147563


My HeathKit Bench DVM is 10M/V and has a mini analog display (think s-meter size) but when I want a meter that can be set to 0 center I use my B&K FETVM.

The one I designed and built has the center zero too.
The center zero is handy to have. I redid front by adding colors to make easy to read.

Dave

 

[SmithDoor]

I built a HeathKit IM-28 VTVM when they were still selling them: in addition to the performance, I liked the form factor better than other VTVM’s.

View attachment 147563


My HeathKit Bench DVM is 10M/V and has a mini analog display (think s-meter size) but when I want a meter that can be set to 0 center I use my B&K FETVM.

It uses a OP AMP it also know as a JFET voltmeter.
Did not put ohms scale just a volt meter . I have a Simpson 260 for ohms.
It can goto 1,000 volts but switches cost to must.
It simpler to build the higher voltage in a probe when need. I have drawings to 500 volts for RF and DC. If want copy just let me know I will send to you in PDF

Dave

 

[ChazzC]

Hi Guys,

One of the problems with Valve volt meters is that they can tell you lies !

I get several volts AC just from leaving the wires loose on the bench ! Now I do know where that voltage comes from and its the local FM radio station.

The point I am trying to make is that you can get deceptive voltage readings that have absolutely nothing to do with the circuit you are measuring.

Due to the open ground: your O'Scope will do the same thing, picking up 60Hz buzz from unshielded conductors (or you if you touch the probe).

 

[SmithDoor]

If any one want to the complete build it is on
https://www.antiqueradios.com/forums/viewtopic.php?f=8&t=421599It shows how I did everything including the faceplate with the redos too.

I did not put here because it not a engine or machine work.

 

[SmithDoor]

Finish improved the meter face and added probe holder

 

[SmithDoor]

Update

It has taking time to make a decision on the last probe.
I decided it would better to use 250 volt and 500 volt range.
Om the probe by switching the range switch from 50 v and 100 volt range

So ranges are
0.5v
1.0v
5.0v
10v
50v
100v
250v
500v.
Giving a wide range for a Transistor VTVM.

See calculations below
This the very last to do

Dave

4.7m
.25m variable resistor
======
4.95m
‐----------------------------------#
1.0m
+ .25m variable resistor
====
1. 25m
≈==============
voltage divider calcs
Voltage Source (VS)
500
Volts (V)
Resistance 1 (R1)
4.95

megaohms (mΩ)
Resistance 2 (R2)
1.25

megaohms (mΩ)
Output Voltage (VOUT)
100.806
Volts (V)

 

[SmithDoor]

My last probe need
Here is drawings for 250 / 500 volt probe.

Note the can be used for bench work 5 volts and 50 volts .

Can be very handy as the AC DC switch in in the probe.

 

[SmithDoor]

Just finished truning my probe housing for high voltage today.
Dave