klemt vof2 vacuum tube voltmeter - Page 1
Forum section: electronics / repair

author: davy peleman
author_rank: Regular Contributor
timestamp: January 07, 2018, 06:33:34 pm
content: i recently purchased an old vacuum tube voltmeter the brand is Klemt the model is vof2. now i cannot find any user manual or schematic. i need to calibrate the thing but there's no indication on the potmeters. so i don't know wich pot is for the 1.5 v calibration and so on. there are 5 potmeters to be adjusted. can anybody who has a manual or anybody who knows how to identify each pot, please help me. everything seems to work fine and i already cleaned it and changed caps and resistors. now to finish the restoration i only need to calibrate the meter.thanks

author: oldway
author_rank: Super Contributor
timestamp: January 08, 2018, 09:02:34 pm
content: I do not think you have any chance to find this electronic schema.But these electronic vacuum tube voltmeters are relatively simple and look alike.You could be inspired by known device schematics and with a bit of reverse engineering, it should not be difficult to solve your problem.Good luck.

author: floobydust
author_rank: Super Contributor
timestamp: January 09, 2018, 01:42:52 am
content: Post clear pictures of the inside pcb or wiring, and should be able to figure it out.

author: duak
author_rank: Super Contributor
timestamp: January 09, 2018, 03:40:07 am
content: The book Vacuum Tube Voltmeters by Rider has a number of design principles and circuits and may be helpful.It can be downloaded from:www.tubebooks.org%2FBooks%2Frider_VTVM.pdf&usg=AOvVaw23kczmYiiY8WLpsqdbJ0TlCheers,

author: davy peleman
author_rank: Regular Contributor
timestamp: January 09, 2018, 05:15:21 pm
content: Thanks alot for the replies. I already thought of reverse engineering, but i rather don't if i don't have to (since it is alot of work) . Also thanks for the schematics and the link to that book. But it's not even one year since i began electronics so some things are difficult to grasp. Maybe i just leave this project until my understanding of electronics is a bit better. But first i will try to solve the problem with your advice. I'm a newbie but the first thing i did was keeping everything safe so i have a variac, isolation transformer and a current limiting light bulb. Thanks again i will make an update on this project so you know how it went.With the schematic, should i follow the wires of the voltage adjustments to the pots to figure what's their function? So if i follow the 1.5 v wire of the adjustement, will it lead me to the pot for adjusting the 1.5V or am i wrong to think like that?Thanks again!

author: floobydust
author_rank: Super Contributor
timestamp: January 09, 2018, 08:09:16 pm
content: A basic VTVM circuit has around 3 trimpots: The AC cal, DC cal, Ohms cal trimpots that would each connect to the function selector switch.The zero adjust and ohms zero are knobs on the front panel. Your VTVM may have more.Fancier VTVM's used a voltage regulator and have additional cal trimpots for each range-selector switch position.Some VTVM's used a 1.5V battery for the ohms excitation. Is this the 1.5V you are talking about?

author: Cyberdragon
author_rank: Super Contributor
timestamp: January 09, 2018, 08:16:13 pm
content: Quote from: floobydust on January 09, 2018, 08:09:16 pmNo, he probably means the 1.5V range pot. The battery is adjusted by the ohms pot.

author: davy peleman
author_rank: Regular Contributor
timestamp: January 09, 2018, 08:44:14 pm
content: has no battery, 5 trimpots, 2 valves and a little valve thats soldered in( i think its a regulator or rectifier) many loomed wires. cannot upload the pictures the files are too big and i'm not good with computers and camera's.i think without pictures it will be difficult to help i'll try to fix that first.already lots of thanks