UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > General Vintage Technology > Components and Circuits

Notices

Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

Reply
 
Thread Tools
Old 26th Nov 2019, 12:46 am   #21
regenfreak
Pentode
 
Join Date: Nov 2018
Location: London SW16, UK.
Posts: 136
Default Re: Measuring a High Voltage, very low current supply?

I use an inexpensive TESTEC HVP40 40KV probe for flyback output measurement. It is basically a resistive voltage divider. It is certainly good for 500V range.

Also I have an "exotic" 10KV AC/DC electrostatic voltmeter (made in London) but its error is only be acceptable in the range of 1kv to 10kV.
regenfreak is offline   Reply With Quote
Old 26th Nov 2019, 2:22 am   #22
Argus25
Nonode
 
Argus25's Avatar
 
Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,557
Default Re: Measuring a High Voltage, very low current supply?

Quote:
Originally Posted by regenfreak View Post
I use an inexpensive TESTEC HVP40 40KV probe for flyback output measurement. It is basically a resistive voltage divider. It is certainly good for 500V range..
Be aware though, these EHT probes are only for static DC measurements, like a CRT's EHT voltage, they cannot be used to inspect a high voltage waveform because they are a very effective LPF due to the very high value dropper resistor and the distributed capacity .

On the other hand, a proper x100 scope probe, that you can measure up to 1500 to 2000v with (depending on the particular one) IS frequency compensated so you can use it for AC wavforms as well as DC measurements.

There are very few frequency compensated EHT probes about, the most famous and an excellent but expensive one is the Tek P6015. They could be filled with dielectric fluid to get the voltage range up to about 30kV. To get to 50kV I had to design my own probe, and its quite a task to get the bandwidth over 1MHz with that voltage range as well as controlling corona discharges.

The Tek probe:

https://au.rs-online.com/web/p/produ...E&gclsrc=aw.ds
Argus25 is offline   Reply With Quote
Old 26th Nov 2019, 2:44 am   #23
Herald1360
Dekatron
 
Herald1360's Avatar
 
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 13,709
Default Re: Measuring a High Voltage, very low current supply?

But with an impedance of only 1 megohm, not a lot of use for the original task here.

Edit: Oops, don't believe everything you read in a RS catalogue entry! It's actually 100 megohm......
__________________
....__________
....|____||__|__\_____
.=.| _---\__|__|_---_|.
.........O..Chris....O
Herald1360 is offline   Reply With Quote
Old 28th Nov 2019, 1:28 am   #24
regenfreak
Pentode
 
Join Date: Nov 2018
Location: London SW16, UK.
Posts: 136
Default Re: Measuring a High Voltage, very low current supply?

yeah i was aware of the Testec 40kv probe frequency response.
I do have a cheapish 1:1000 HV scope probe but i dont really do much scoping of HT waveform unless i really know what i am doing as things can go south easily even with isolation transformer!!!
Ideally one should get a HV differential probe but one man' s investment of a hobby is always limited by how deeper his pocket is.
regenfreak is offline   Reply With Quote
Old 28th Nov 2019, 3:28 pm   #25
PJL
Dekatron
 
Join Date: Sep 2005
Location: Seaford, East Sussex, UK.
Posts: 4,275
Default Re: Measuring a High Voltage, very low current supply?

An unloaded flyback converter will have terrible regulation so a fixed load should be included that is around the maximum current draw of the GM tube.
PJL is offline   Reply With Quote
Old 28th Nov 2019, 4:36 pm   #26
Martin G7MRV
Heptode
 
Join Date: May 2008
Location: Selby, North Yorkshire, UK.
Posts: 768
Default Re: Measuring a High Voltage, very low current supply?

Quote:
Originally Posted by PJL View Post
An unloaded flyback converter will have terrible regulation so a fixed load should be included that is around the maximum current draw of the GM tube.
Most G-M flyback type supplies use either zeners or gas-discharge (neon bulbs) feedback for regulation.

A version i've built using just resistive feedback from prior to the flyback diode is rather poor, varying +/- 10-20V, but eventually settling down and staying within a few volts of the 430V it was designed for. Even while settling it is within the G-M plateau, but its still not a design i'll be using with expensive tubes.
__________________
I got food in ma belly and a license for ma telly

My Blog - http://g7mrv.blogspot.com
Martin G7MRV is offline   Reply With Quote
Reply

Thread Tools



All times are GMT +1. The time now is 4:05 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Copyright ©2002 - 2019, Paul Stenning.