If you need assistance, please send an email to forum at 4hv dot org. To ensure your email is not marked as spam, please include the phrase "4hv help" in the subject line. You can also find assistance via IRC, at irc.shadowworld.net, room #hvcomm.
Support 4hv.org!
Donate:
4hv.org is hosted on a dedicated server. Unfortunately, this server costs and we rely on the help of site members to keep 4hv.org running. Please consider donating. We will place your name on the thanks list and you'll be helping to keep 4hv.org alive and free for everyone. Members whose names appear in red bold have donated recently. Green bold denotes those who have recently donated to keep the server carbon neutral.
Special Thanks To:
Aaron Holmes
Aaron Wheeler
Adam Horden
Alan Scrimgeour
Andre
Andrew Haynes
Anonymous000
asabase
Austin Weil
barney
Barry
Bert Hickman
Bill Kukowski
Blitzorn
Brandon Paradelas
Bruce Bowling
BubeeMike
Byong Park
Cesiumsponge
Chris F.
Chris Hooper
Corey Worthington
Derek Woodroffe
Dalus
Dan Strother
Daniel Davis
Daniel Uhrenholt
datasheetarchive
Dave Billington
Dave Marshall
David F.
Dennis Rogers
drelectrix
Dr. John Gudenas
Dr. Spark
E.TexasTesla
eastvoltresearch
Eirik Taylor
Erik Dyakov
Erlend^SE
Finn Hammer
Firebug24k
GalliumMan
Gary Peterson
George Slade
GhostNull
Gordon Mcknight
Graham Armitage
Grant
GreySoul
Henry H
IamSmooth
In memory of Leo Powning
Jacob Cash
James Howells
James Pawson
Jeff Greenfield
Jeff Thomas
Jesse Frost
Jim Mitchell
jlr134
Joe Mastroianni
John Forcina
John Oberg
John Willcutt
Jon Newcomb
klugesmith
Leslie Wright
Lutz Hoffman
Mads Barnkob
Martin King
Mats Karlsson
Matt Gibson
Matthew Guidry
mbd
Michael D'Angelo
Mikkel
mileswaldron
mister_rf
Neil Foster
Nick de Smith
Nick Soroka
nicklenorp
Nik
Norman Stanley
Patrick Coleman
Paul Brodie
Paul Jordan
Paul Montgomery
Ped
Peter Krogen
Peter Terren
PhilGood
Richard Feldman
Robert Bush
Royce Bailey
Scott Fusare
Scott Newman
smiffy
Stella
Steven Busic
Steve Conner
Steve Jones
Steve Ward
Sulaiman
Thomas Coyle
Thomas A. Wallace
Thomas W
Timo
Torch
Ulf Jonsson
vasil
Vaxian
vladi mazzilli
wastehl
Weston
William Kim
William N.
William Stehl
Wesley Venis
The aforementioned have contributed financially to the continuing triumph of 4hv.org. They are deserving of my most heartfelt thanks.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
I can't see much in the video either. The only thing I noticed was some light being reflected by the anode connection.
What color is the light you are seeing?
If you see purple corona-like light, it is possible the tube is gassy. In such case, leave just the heater turned on for 48 hours to activate the getter.
Remember the supply voltage for the GU-81 must be derated with frequency, but 800 volts is really little.
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
What you can see in the video (which is just a bit of light) is pretty much all i can see. I can see where the defect is alot clearer, but i don't have a camera or camcorder that could help make it any clearer. A sketch is a good idea, but i have never sketched anything. I will try to draw a sketch, but if it looks as bad as i expect i won't bother uploading it.
It isn't a hole in the plate, because where the glow is emanating from is a solid hunk of whatever material the plate is made out of (i cannot find any info on this). There is not a spot weld where the bad connection is, it just seems to be wedged in between a piece of ceramic and the plate.
It doesn't seem to be gassy, the only color i can see is that very vague blue glow on the glass as with many/most tubes. Also, the getters look fine (they aren't white, a somewhat lighter grey than the plate). The color is white as far as i can tell.
I will try to find some high quality pictures on the internet that i can use, perhaps draw an arrow in paint, and update this post.
Edit: I stole my dad's camera (which he does not need 2 cameras anyway, i need a new one) to take this pic. You can see where the metal thing that connects to the top cap curves (at the bottom) and goes in between that white support and the plate. Somewhere around there is where the glow was coming from. But wait! Now that light is no longer there! I guess it sorted itself out when i ran higher powers yesterday, perhaps thermal expansion made the connection better or something, i don't know.
Another edit: Also, is it normal for the filament to heat unevenly upon turning it on? I use a couple of 2.7 ohm resistors in parallel to slowly start the filament up, but once i turn the switch which bypasses the resistors on, i can tell one half of the filament gets hotter faster. This worries me a little bit, especially since i sometimes see sparks when i turn the filament on (once again, i *always* use the resistors to limit inrush current). It may be a poor connection under the tube itself somewhere in the metal 'base'. I mean, surely if i saw sparking inside of the tube something would have died by now. Perhaps i am just being paranoid, but there was *no* packing material, and it was shipped from China to the US. Just sitting in a box.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
You wrote, "i can tell one half of the filament gets hotter faster." So are both halves of the heater different brightness after the temperatures settle, or just during the heating up time?
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
Dr. Kilovolt wrote ...
You wrote, "i can tell one half of the filament gets hotter faster." So are both halves of the heater different brightness after the temperatures settle, or just during the heating up time?
Gah, i knew i forgot to say something. They do seem to run at the same temperature once the current settles. I just don't want one side to be too cool and cause too much voltage to be dropped across the other half and it break. That would break my heart! However, i have run the filament for a long time, and it seems to be alright...
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Arcstarter wrote ...
Now that light is no longer there! I guess it sorted itself out when i ran higher powers yesterday, perhaps thermal expansion made the connection better or something, i don't know.
When valves aren't used for long periods of time - or perhaps have never been used at all since leaving the factory - they will often be slightly 'soft' - i.e. gases adsorbed/absorbed onto/into the electrode architecture and the glass seeps out into the vacuum, and will ionize with a glow when sufficient voltage is applied.
Large, costly power valves often came with detailed instructions on how to condition them for full power use via an incremental series of increasing anode voltage steps - sometimes spread over tens of hours - until all the unwanted gas had once again been taken up by the glass and metal structures, and the full high vacuum was restored. In X-ray tubes, this important conditioning process is called 'seasoning.'
This is why I think the anomalous glow in your valve seems to have disappeared after a little use, but guesswork is no substitute for measurement in fault diagnosis.
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
I wish i could say that i have all of the equipment to ensure i drive my tubes correct, and to season them, but i don't. I can heat the filament for long periods of time (which i already sort of have, if an hour every once in awhile counts), but i do not have any transformers that would come close to what i would call reliable. Leaving a HV supply on for long periods of time isn't something i am willing to do, because i know i would accidentally touch it. So, as it turns out, i am a tube abuser .
Also, the spark is back, but it is not as bright, and it moved... I'm not going to worry too much about it, because if it doesn't kill the tube, i probably will .
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
I always leave larger tubes to "getter" at least overnight, preferrably at least 24 hours. I just turn on the filament. It may not be as efficient as the method described by Proud Mary, but its better than nothing.
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
Nah wrote ...
This is a little confusing for me...
Arcstarter, did you use the supresser as a control grid???
That i did. I never tried it at any higher voltages, so you can rest assured that i have no plans murdering my tube . Also, the only thing i ever did to the suppressor grid was input a variable voltage (0 to -100vdc), so nothing that would harm it.
If the suppressor worked as well as the actual control grid i probably would have tried to use more current on the plate and use AC on the suppressor, but it is almost impossible to kill a tube if you pay attention. I always look at the screen grid to make sure it doesn't get too hot, and i try to check the control grid the best i can but it is hard to see. However, you could see it if it where red, despite the brightness of the filament, im sure.
At Dr. Kilovolt, at this point im sure the filament has been on for about 12 hours, though it has been intermittent. I just don't think it would be a good idea to run my filament transformer for that long. It is only running 12w more than it is rated, but it gets damn hot, and not to mention it is 102 F outside and this tube heats my room up fast .
This site is powered by e107, which is released under the GNU GPL License. All work on this site, except where otherwise noted, is licensed under a Creative Commons Attribution-ShareAlike 2.5 License. By submitting any information to this site, you agree that anything submitted will be so licensed. Please read our Disclaimer and Policies page for information on your rights and responsibilities regarding this site.
GU-81M datasheet.
. 
.
