Transistor VTVM made common parts.

[Smithdoor]

Transistor VTVM made this from common parts.

Dave

[Chrispy57]

Hi Dave,
welcome to the Forum. That looks like an interesting, well documented design that you have shared here. A couple of questions - is that a centre-zero meter you have used (pointer mid-scale with no obvious input voltage in the photo), and which 4.5V batteries are you using?

Cheers
Chris

[Smithdoor]

It is 9 volts and the centre is 4.5. I used six AA batteries.
Yes you can zero to centre 1 volt to 100 volts.

If you want to zero at 0.5 volts you need to use 8 AA batteries. The circuit can use two 9 volt batteries too.

In America I have almost received 16,000 views to date.
It was built from parts from Amazon and Walmart.
The front face in photo print on a Laser printer and then covered with .09" plexiglass from Home Depot
I would post link here but some sites do not like it.
But web search [ transistor VTVM ]

Photo of front under construction.

Dave

[Smithdoor]

I updated the notes on schematic and added the AF and RF probes.
Include a PDF schematic for a clearer view of transistor VTVM

PS

If you wonder why did not put a ohms scale in the meter face would take a long time to make and I have a VOM that does same job.

Dave

[Smithdoor]

Here is a drawing on how made probe from a old wind-chime copper tube can be used too.

[dragonser]

Hi,
this info is very helpful, thank you !

[Smithdoor]

Originally Posted by dragonser

Hi,
this info is very helpful, thank you !

You're welcome

[Smithdoor]

Originally Posted by dragonser

Hi,
this info is very helpful, thank you !

If need more info let me know.
All parts came from Amazon or Walmart.

When look at this project it was 4 parts.

1) good simple schematic
2) good face plate not use a pen.
3) meter face the best low cost was a fine line sharpie set.
4) great simple probes. It base Eico thin design it even thinner than Eico.

Dave

[Smithdoor]

Quadruple probe for AF and RF work.

Dave

[Smithdoor]

Here is a Quadruple AC, AF & RF PROBE schematic.
It schematic fitting in to a probe.
Not tested at this time.

Dave

[Smithdoor]

Here probe I making for 20Hz to 50Mz
This base on well know tube type ac for VTVM

Dave

[Smithdoor]

Here is a Eico VTVM AC AF schematic I found last night. It looks good and simple for probe.
It one last design of a VTVM by Eico.
Holding on probe till I can research this schematic.

Dave

[Smithdoor]

Here is schematic I am using for probes after months of searching. The last thing in this build

Dave

[Smithdoor]

Here is the schematic of the VTVM in pdf file for printing. All data need is on the schematic for building

Input resistance is 11MEG
Probes schematic DC to 250Mhz.


Dave

[Chrispy57]

Hi Dave,
the 6 potentiometers, R16 to R20, are each 10K and are being used to adjust for a voltage range of 0.5V to 100V, which is a 200:1 ratio of voltages. Are these multi-turn potentiometers, and how difficult was it to set each one accurately?

A minor observation, the designation R11 has been used twice on the schematic.

Cheers
Chris

[Smithdoor]

R16 - 20 is just a standard potentiometer
Not hard to adjust it is only a 50Ua meter.
I started with one potentiometers for adjusting the meter calibration. I found that I would get a few volts on each range . I fix by using a calibrated for each range. Now every range is on mark.

A multi-turn potentiometer would be nicer if had do over again.

Thank you I will fix R11 error

The VTVM is finished for few months now and working great.

I may ad a 5 to 1 probe for 500 and 250 volt range.

Dave

PS:
If wonder why I do not put 500 or 1000 volt rage on meter is the case can have 500 or 1000 volts or I would loose my shielding by fix the 1,000 volts on case

Originally Posted by Chrispy57

Hi Dave,
the 6 potentiometers, R16 to R20, are each 10K and are being used to adjust for a voltage range of 0.5V to 100V, which is a 200:1 ratio of voltages. Are these multi-turn potentiometers, and how difficult was it to set each one accurately?

A minor observation, the designation R11 has been used twice on the schematic.

Cheers
Chris

[Smithdoor]

clear view of schematic

[Smithdoor]

I will keep even informed on any updates on the Transistor VTVM.
My next equipment build will be a AF generator.

I started designing in Dec 29 2022 the VTVM.
First simply Transistor did not work well.
Next was different chip good no soldering needed just by a LF353 the chip is so cheap I use as fuse too. Add a diodes to meter protection.
I add calibration to all voltage range as want to right on mark for voltage.
Some pass writing I spent researching probes on to my first choes was best.
The VTVM can goto 1,000 volts , I did want 1,000 volts in the VTVM so if need to read 1,000 volt and the sentevity of a VTVM. My VOM will cover 1,000 volts goes to 1,000 volts both AC and DC it also reads ohms too. I can buy probe foe 15,000 to if ever need to read that high.

You can buy a kit but they look cheap too.
I did build from schematic in 1960's but loss in moving.
There only two I do not build and new RF generator and new VOM. I do this so they are factory calibrated. Even my Eico Oscilloscope is from kit back in the 1960's

Dave

[Smithdoor]

Here is a schematic of my next probe.
It is RF , AF/AC and DC.
The schematic shows max voltage of 150v
You Chang the resistors for 250 , 500 and a 1,000 volts.

Dave

[Smithdoor]

Updated schematic