• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

VTVM or FETVM?

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#101
anatech said:
I'm talking about repair advice and upgrade advice. Schematics are factual unless running production changes have been made. You've always got to check. I'm talking about all equipment, test and audio. Test equipment normally has less silliness associated with it.

Most practicing technicians and engineers in any field do not have time to post on the internet, and certainly will not be producing a YOUTube video! People will offer advice without having actual trained experience, and they may argue their point to the mat while being dead wrong. That seems to be the nature of the internet. It's a place where anyone can be an expert. Others read this information, accept is as correct and act on it. They and their equipment may suffer for it.

Common sense is your best friend. That and talking to someone who actually worked in the field successfully. You're doing that, so you are on the right path.
Click to expand...
I agree 👍
 
#103
To be honest with you, test equipment from the late 1960's on up is very good. HP made some of the best out there.

Sometimes newer parts can improve performance, and slightly different circuit techniques also. But 1940's and 1950's gear will be limited.
 
#104
jackinnj said:
Before general availability of JFETs, HP used positive feedback in their transistorized voltmeters!

I use the Fluke 77 as my daily-user, and an Eico 222 which I purchased over 50 years ago for HV. As noted by other correspondents, all of these are useful for sine but not for noise measurements. Jim Williams did a wonderful application note describing the pitfalls! Depending on the time of day and alignment of the stars you can sometimes purchase an HP3478 for a knock-down price and it is very accurate RMS-wise).

(I have an HP and Fluke calorimetric true, really, really true RMs meters!)
Click to expand...

Yeah... the HP-IB interface. We used to purchase the 3478 DMM and install them in our test stations.... with scanners, etc... and hook up a computer for them.

We called them ATE. Excellent machine.
 
#105
Stuey said:
Maybe the movement is meant to be damped in these Micronta's by design. Mine is certainly quite damped compared to another cheap lab voltmeter I have which positively jumps to attention.
Click to expand...
Agree,
Looking at this from pure physics perspective... Newton's 2nd says A= F/M.
So acceleration will be slow if force driving meter circuit is low, and/or mass of needle is high.
Force of driving circuit is most likely low- being battery powered... Whereas the VTVM is 120 VAC powered
Stuey said:
Penetrating oil (if you mean like WD40) is the bane of any watch or clock repairer! It eventually gums the works as the aromatics gas off.
Click to expand...
Penetrating oil is much thinner than WD40... It runs like water.
If decide to try, it can be cleaned out easily if ineffective. I'm thinking it won't work- real issue is more circuit driver related
 
#106
anatech said:
To be honest with you, test equipment from the late 1960's on up is very good. HP made some of the best out there.

Sometimes newer parts can improve performance, and slightly different circuit techniques also. But 1940's and 1950's gear will be limited.
Click to expand...
Ok I equipment from 1940's.
My electronic equipment I purchased new in 1960's to 2017.

Sorry for the confusion.

I found if got new did not have to undo before trusting the electronic equipment.

My dream job was in electronics and had formal education. But did different line because I made lot money starting in high school to buy electronic test equipment.

What learn in electronics help in the other field.

I almost got a job at the local Lafayette store but had wait till turn 18 for $1.40 hrs. The other work paid $3.40 hrs and quickly move up.
{Inflation Calc in 1969 $3.40 today is $28.00 hr.}

Dave
 
#107
Here is probe for just AC DC upto 250 volt work .
Screenshot_20230909-122734_Drive.jpg
 
#108
Those are rated for 40 PIV. Look at fast signal diodes as they will also have lower capacitance.

Keep in mind that the upper frequency response is dependant on a few things. Not only that, but you'll have to put a compensation capacitor across the probe dropping resistor (variable ), just like an oscilloscope probe if you are trying for RF frequencies. That also reduces the AC impedance at higher frequencies - just like an oscilloscope probe.
 
#110
Hey Dave,
That will have a falling frequency response, so you are not good to 250 MHz. Probably not even to 10 MHz depending on acceptable error.

What you need to do is have a leveled RF oscillator, and a certified (calibrated) oscilloscope you absolutely know for sure is flat way past 250 MHz in order to characterise that probe. Then you measure the source while monitoring the levels. Also watch for a non-flat response, it may dip and come back up, or have a hump.

Not trying to be a downer, but I am certified for instrument calibration and certification. I've seen all kinds of things.

-Chris
 
#111
anatech said:
Those are rated for 40 PIV. Look at fast signal diodes as they will also have lower capacitance.

Keep in mind that the upper frequency response is dependant on a few things. Not only that, but you'll have to put a compensation capacitor across the probe dropping resistor (variable ), just like an oscilloscope probe if you are trying for RF frequencies. That also reduces the AC impedance at higher frequencies - just like an oscilloscope probe.
Click to expand...
Here is my 250Mhz probe it works great it was lower frequency is probe I need .

I test this probe to 150MHZ

Dave

20230226_195229.jpg
Screenshot_20230910-071624_Drive.jpg
 
#112
Okay, how did you verify it's performance?

I'm not arguing or doubting you. But 150 MHz brings in significant effects from cable and probe body capacitance. You will see these effects even at 10 MHz and lower.

Your calibration setup is critical, it has to be done correctly or your results are not worth anything.
 
#113
I did not have way to calibrate the probe at 150Mhz.
I when spec of signal generator for voltage.
Since use for adjustinging above 455Khz to only peck voltage calibration is not need.

The new probe is so I can do calibration the probe for 30hz to 400hz.

Dave
 
#114
Hi Dave,
I guess if you are only looking for peaks, it will do that. Your indication will be lower than the actual voltage and that may be a problem at low signal levels. I can assure you your probe needs compensation if you expect it to be even roughly accurate.

RF generators with a "leveled output" should be accurate depending on your connections. Here you have to be careful and maintain proper loading (50R for test and measurement, 75R for consumer RF). Everything depends on the details to characterize a probe. That's to keep your calibration source accurate - I know you have a high impedance input probe at low frequencies. That will drop as the frequency increases.

Any standard generator cannot be trusted to maintain a flat output. Those must be monitored with a known accurate meter or 'scope.
 
#115
It is what have and not high end it is basic just for adjusting radios.

It is close .

My DC side is on the mark as close as I can adjust.
The AC voltage I test to from 10hz to 5khz with my Simpson.

So the new probe fits what I can calibrated.

Dave
 
#116
That's cool, but you said it was good to 150 MHz, and 250 MHz earlier. Your Simpson may not be good to 5 KHz,a and the spec is the -3dB point - not flat.

All I'm trying to do is have you understand the limitations of your equipment. I am not trying to criticize at all.
 
#118
anatech said:
Any standard generator cannot be trusted to maintain a flat output. Those must be monitored with a known accurate meter or 'scope.
Click to expand...
Agree,
Checked my refurb'ed Eico 324 RF generator's output vs freq over voltage on my 'scope... Found that output voltage decreased significantly as freq increased. IIRC- P to P @ 100mhz (limit of my scope) was 30mv.
For RF generation in tuning receivers, that amount is fine, but it would have been nice to have that 30mv level throughout total frequency bands.
Jim
 
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#120
Hi Jim,
Your generator may perform better with a 50 ohm load if you haven't got it loaded.

Hey Dave,
TV tuners have AGC and all kinds of equalization. Just because something "works" does not mean it works properly. Earlier equipment from the 1970's and 1980's were pretty fast and loose with specs and performance (ask me how I know). But if you use a name-brand (ie, Panasonic, Leader or something decent in consumer electronics service) you should be a lot better. An HP absolutely will be correct.

An old HP 8640B would be excellent. I have one (at least), and currently use HP 8656B and HP 8657A, plus a new Keysight N9310A generator. I have the classic FM generators and also a Panasonic VP-8131A. The HP and Keysight stuff is absolutely bang-on, the Panasonic is pretty good.

I also have spectrum and network analyzers, and those really help when a hack was "aligning" a tuner. Real life savers. HP of course!
 
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