Tube DIY Asylum

Do It Yourself (DIY) paradise for tube and SET project builders.

Return to Tube DIY Asylum

Message Sort: Post Order or Asylum Reverse Threaded

Oops..........

69.40.60.153
Posted on December 12, 2014 at 12:29:44
vinnie2
Audiophile

Posts: 4481
Location: North Carolina
Joined: September 28, 2013
 Well I guess the filaments of at least some tubes are tougher than I thought they would be. I was trying out a different driver for the 91A and I neglected to change the filament transfo. The old driver was a 310A that needs 10v, and the new driver is a 6C6 which needs 6v for the filament.
It must have been a full 5 minutes before it dawned on me what I had done. It sounded a tad strange, but I had not heard this tube before. It was when I noticed the filaments glowing brighter that I thought they should that I yelled "oh crap!" and jumped for the variac and shut it down.
I am sure I have shortened the life expectancy of those two tubes by quite a bit, but I was truly amazed that both of them still worked fine when I hooked them up to a 6v filament transfo.
This makes me curious as to how much abuse in filament voltage the average tube filament can take. I mean that was more than 50% for Pete's sake! Does anyone know for sure?
Also, this was AC on the filaments, not DC. Does that make any difference?

 

Hide full thread outline!
    ...
RE: Oops.........., posted on December 12, 2014 at 12:42:36
Chip647
Audiophile

Posts: 2649
Location: The South
Joined: December 24, 2012
 You could probably get many hours on those over-voltaged heaters until they failed. Tubes are pretty rugged as a whole. You can screw-up and red plate a tube and if you catch it relatively soon the tube will survive just fine.

5 minutes likely did very little damage if any.

 

RE: Oops.........., posted on December 12, 2014 at 15:58:11
drlowmu
Manufacturer

Posts: 9730
Location: East of Kansas City
Joined: January 10, 2005
 Depending upon vintage, I am under the impression that filaments and cathodes have certain types of coatings on them. If you operate the tube as far off as you did, I can not imagine the coating will act the same as if the tube always was within 5% of its rated voltages. BTW, I usually LIKE -5% of rated on my filaments.

Don't feel bad, you can buy more tubes, and its all part of the learning process. You won't do it again I betcha.

Jeff Medwin

 

RE: Oops.........., posted on December 12, 2014 at 18:09:47
vinnie2
Audiophile

Posts: 4481
Location: North Carolina
Joined: September 28, 2013
 I will be curious to see if they do have a shorter life or not. I always thought that much over would have vaporized the filament. Still wondering if AC or DC matters.

 

RE: Oops.........., posted on December 12, 2014 at 18:10:27
vinnie2
Audiophile

Posts: 4481
Location: North Carolina
Joined: September 28, 2013
 It will be educational to see how long they last.

 

RE: Oops.........., posted on December 12, 2014 at 18:41:37
Paul Joppa
Industry Professional

Posts: 7295
Location: Seattle, WA
Joined: April 23, 2001
 In the manufacturing process, heaters are subjected to 1.5 times normal, sometimes more, for short periods like 30 minutes.

If I recall correctly, raw tungsten (light bulbs for instance) have a lifetime inversely proportional to something like the 15th power of the voltage. (10/6)^15 times 5 minutes is about 175 hours of lifetime lost. No biggie.

 

RE: Oops.........., posted on December 13, 2014 at 06:30:05
vinnie2
Audiophile

Posts: 4481
Location: North Carolina
Joined: September 28, 2013
 Thanks Paul. That's very interesting and the first time I have heard of either fact. Do you know if AC or DC makes any difference? Not likely I suppose.

 

RE: Oops.........., posted on December 13, 2014 at 12:06:26
Triode_Kingdom
Audiophile

Posts: 10042
Location: Central Texas
Joined: September 24, 2006
 "I can not imagine the coating will act the same"

I would think that some VTs could have their coating degraded within a minute or two at 2X the voltage. At that point, it's no longer a question of how long the tube will last as much as whether it still functions properly. A test for peak current capability might indicate that significant degradation has occurred in the scenario being discussed.

 

RE: Oops.........., posted on December 14, 2014 at 06:53:31
xaudiomanx
Audiophile

Posts: 3647
Joined: August 16, 2004
 I do know that if you put a sneeze more voltage on the filament of a 26 tube the tube fries almost instantly.

 

RE: Oops.........., posted on December 14, 2014 at 14:04:19
vinnie2
Audiophile

Posts: 4481
Location: North Carolina
Joined: September 28, 2013
 I think some tube filaments are more delicate than others, especially the lower voltage filaments.

 

Page processed in 0.024 seconds.

[ Top Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2024, Audio Asylum, all rights reserved ]
[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]