Go Back   Home > Forums > >

Equipment & Tools From test equipment to hand tools

Testing a VTVM?
Testing a VTVM?
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools
Old 3rd December 2020, 04:26 PM   #11
JMFahey is offline JMFahey  Argentina
diyAudio Member
 
JMFahey's Avatar
 
Join Date: Mar 2009
Location: Buenos Aires - Argentina
Quote:
Originally Posted by PRR View Post
Being an AC VTVM, the trick of calibrating against a fresh flashlight cell is not useful (no AC in a battery).
Well, yes and no.
A classic VTVM is *always* a DC measuring instrument, just check classic schematics.
The trick they use to measure AC is thanks to a probe, which does the rectification and conversion.

They generally use 2 kinds:

* the "RF probe" type.
It uses a series cap which must also stand any DC voltage present so typically 600V rated, diode (usually Germanium) which generates a positive voltage and a high value series resistor (usually 4M7 or so) which in series with 10M input impedance scales doen the peak rectified voltage to RMS equivalent.
Click the image to open in full size.

*the "Peak to Peak" probe
It uses a full wave rectifier-doubler.
Sometimes a vacuum tube double diode is used, think 6H6, 6AL5 and similar.
Meter panel has a Peak to Peak scale, and old TV schematics included waveforms and their PP values.

So in a way, "DC testing witha battery" is still valid, as long as your AC probe is not damaged.

Quote:
Calibration is basically comparison to a "known-good" AC meter on the same source. If you were a Calibration Laboratory you would have a known-size AC source; but clearly you are not there yet.
yes, that is the universal way, works every time.
__________________
Design/make/service musical stuff in Buenos Aires, Argentina, since 1969.
  Reply With Quote
Old 4th December 2020, 04:47 AM   #12
PRR is online now PRR  United States
diyAudio Member
 
PRR's Avatar
 
Join Date: Jun 2003
Location: Maine USA
Testing a VTVM?
Quote:
Originally Posted by multisync View Post
...I saw VTVM and presumed it was similar to the VTVM multimeter I had.
Me too.

Quote:
Originally Posted by JMFahey View Post
Well, yes and no.
A classic VTVM is *always* a DC measuring instrument, just check classic schematics.
The trick they use to measure AC is thanks to a probe, which does the rectification and conversion.....
Did you look at the documentation?? This is an AC-ONLY amplifier meter. It will read to 0.03V FS which is well beyond an "RF probe" on a DC meter. It is a cheap version of the Ballantine 300 or the H-P AC-only meters. (Or multisync's Stark tube AC millivoltmeter.)
Attached Images
File Type: jpg sensitive_electronic_voltmeter_300d_629692.jpg (22.2 KB, 19 views)
File Type: gif Ballantine300Dschem-42.gif (32.3 KB, 21 views)

Last edited by PRR; 4th December 2020 at 04:49 AM.
  Reply to this post

Reply


Testing a VTVM?Hide this!Advertise here!
Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Eico NOS Mdl 232K VTVM Peak-to-Peak VTVM KIT UNOPENED HolySmokes Swap Meet 0 27th January 2012 11:01 PM
diy Heathkit VTVM probe... sklimek Parts 11 3rd December 2010 12:11 AM
Battery Question vs VTVM Alaska Bill Equipment & Tools 5 27th November 2010 05:32 AM
HP 410B VTVM (refurbished and recalibrated) n_maher Swap Meet 3 23rd September 2008 06:23 PM
Is a VTVM useful? d1camero Tubes / Valves 10 31st January 2008 06:12 AM


New To Site? Need Help?

All times are GMT. The time now is 09:48 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.
Copyright ©1999-2021 diyAudio
Wiki