Test pentode grids without a tester - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

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
Thread Tools Search this Thread
Old 25th October 2007, 07:34 PM   #1
diyAudio Member
diegot's Avatar
Join Date: Sep 2004
Location: Brazil
Default Test pentode grids without a tester

I have three rare EL34 and want to test their grids for sorts and/or melting.

My ideia is to power the filaments and with a variable low voltage supply at the anode put a small amount of current (20mA for example) through the tube and them meassure the voltage at the grids.

This method will work?

Thanks for any help.
  Reply With Quote
Old 25th October 2007, 08:54 PM   #2
diyAudio Member
HollowState's Avatar
Join Date: Aug 2006
Location: Taxland, New Jersey
Hi Diego,
The method you propose may detect some voltage on the grid (G1 or G2) due to space charging. But this will be inconclusive as to whether it's leakage between elements or not.

Don't heat the tube. Leave it cold and apply a variable DC voltage through a series resistor and a milliamp or microamp meter between the grid of interest and the element next to it. (Your DC supply may already have a milliamp meter?) A good tube, when cold, should have no leakage between any elements and should withstand at least 100 volts on G1 and more on the rest. (NOT heater to cathode)

This test is called a DC hypot test and will reveal any leakage or shorts that a regular low voltage ohmmeter will not. Polarity is not really important in this case since the tube is cold.

1944: 18 year olds storm the beach of Normandy into almost certain death.
2017: 18 year olds need a safe place because words hurt their feelings.
  Reply With Quote


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Precision Test Equipment tube tester zigzagflux Equipment & Tools 13 24th July 2009 03:47 AM
Why don't pentodes require aligned grids? Ty_Bower Tubes / Valves 12 5th January 2009 09:21 AM
„New“ Pentode – measuring resistance between grids G2 and G3 – any idea? MRupp Tubes / Valves 5 5th January 2008 06:24 PM
Tube tester and noise test Jeffy74 Equipment & Tools 1 7th March 2004 06:49 PM
Not connecting grids/anode can hurt tube? Redemption Tubes / Valves 6 14th January 2004 11:20 AM

New To Site? Need Help?

All times are GMT. The time now is 10:16 PM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2