Plasma ball in tube

wicked1 · 10:46 PM

My rectifier has been arcing. I made a couple of changes (diodes in series w/ plates, and changed input cap). Now it usually starts fine, but occasionally (maybe 1 in 5 pwer cycles) there's a tiny spark that Ive noticed falls down the tube. I thought what I saw falling was some coating coming off the filament, but several days ago I noticed one fell to the bottom of the tube and bounced across to the other side and then up towards the top before it disappeared!!
So, lately Ive been watching closely every time I turn it on, and it did it again today. Not such a dramatic bounce, but it was definitely a tiny ball of plasma.

(ive got a different post about what could be causing the rectifier to spark, and am waiting on some parts to arrive to try to fix it.. just wanted to mention the interesting thing it's doing)

nhuwar · 13th December 2009, 11:07 PM

I doubt this is a plasma ball, but crazier thing have happened. But what you could have happening is some serious heating and a little bit of molten metal flying around in there. At any case you need to replace that tube before you have it catastrophically and take something else with it.

Nick

Matt.B.H. · 13th December 2009, 11:15 PM

I completely agree,
You need gas for plasma, if it was gassy you would know about it (glowing, arcing etc). Replace it quick.
Cheers Matt.

wicked1 · 14th December 2009, 01:00 AM

hmm ok.. It's quite reactive, though!
and well, it doesn't matter what tube I put in there right now... They all spark.
Need to put some current limiters on my amp, I guess. Everything tests fine, other than I get a HUGE surge at power up. (goes past the range of my meter for a 1/2 second)

nhuwar · 14th December 2009, 01:05 AM

Whats the rectifier tube and what is the size of the filter?

wicked1 · 14th December 2009, 01:06 AM

5u4g
clc
20uf-6h/150ma-180uf

wicked1 · 14th December 2009, 01:12 AM

One thing I failed to mention in the other thread about this, is that I have a negative supply coming off the same 2ndary of the power tx. That goes through a couple of diodes and 100uf-R(forget what)-100uf. Maybe those charging quickly is causing or helping the surge.
Well, it doesn't matter. I know the design of the amp is good (it's a tubelab SE, so there are plenty of them out in the world.. I used default values for everything). I think my power tx or choke are somehow causing it. They are literally the only components that haven't been replaced.
(well I didn't replace every resistor, but I did test them while trying to solve this issue)

nhuwar · 14th December 2009, 01:13 AM

Well that seem fine to me. Maybe one of the more experienced can chime in and give you more help then I.

Nick

Arnulf · 14th December 2009, 03:25 PM

Quote:

Originally Posted by wicked1

5u4g
clc
20uf-6h/150ma-180uf

Can you reduce the capacitance behind the choke temporarily to approximately 1/3 or 1/4 of what it is now and test it again with those different rectifier tubes you mentioned ?

wicked1 · 14th December 2009, 03:34 PM

I have, and I got no sparks (But, I don't always get sparks even with the normal capacitance). I left it like that for several days, maybe 10 power cycles, and it seemed fine.
But otherwise the choke tests fine (has the DCR it should), and seems to function properly after the initial surge.

My power TX is a hammond, and has never been right.. It's supposed to be 250-0-250, but I get about 300-0-300 out of it! Even under full load, it's putting out way more power than it should. So, it's definitely a suspect too.

I hope the problem is just the initial surge, and I have some cl-90's on the way to hopefully fix that.
Once I have some extra money, I guess I'll purchase a new power tx and choke.. Then I will have replaced every single component in this amp.. (always w/ better parts, so Im not complaining)

13th December 2009, 10:43 PM	#1
wicked1 diyAudio Member Join Date: Jan 2008	Plasma ball in tube My rectifier has been arcing. I made a couple of changes (diodes in series w/ plates, and changed input cap). Now it usually starts fine, but occasionally (maybe 1 in 5 pwer cycles) there's a tiny spark that Ive noticed falls down the tube. I thought what I saw falling was some coating coming off the filament, but several days ago I noticed one fell to the bottom of the tube and bounced across to the other side and then up towards the top before it disappeared!! So, lately Ive been watching closely every time I turn it on, and it did it again today. Not such a dramatic bounce, but it was definitely a tiny ball of plasma. (ive got a different post about what could be causing the rectifier to spark, and am waiting on some parts to arrive to try to fix it.. just wanted to mention the interesting thing it's doing) Last edited by wicked1; 13th December 2009 at 10:46 PM.

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13th December 2009, 11:07 PM	#2
nhuwar diyAudio Member Join Date: Jan 2007 Location: Tomball Texas	I doubt this is a plasma ball, but crazier thing have happened. But what you could have happening is some serious heating and a little bit of molten metal flying around in there. At any case you need to replace that tube before you have it catastrophically and take something else with it. Nick

13th December 2009, 11:15 PM	#3
Matt.B.H. diyAudio Member Join Date: Jul 2009 Location: Cheltenham	I completely agree, You need gas for plasma, if it was gassy you would know about it (glowing, arcing etc). Replace it quick. Cheers Matt.

14th December 2009, 01:00 AM	#4
wicked1 diyAudio Member Join Date: Jan 2008	hmm ok.. It's quite reactive, though! and well, it doesn't matter what tube I put in there right now... They all spark. Need to put some current limiters on my amp, I guess. Everything tests fine, other than I get a HUGE surge at power up. (goes past the range of my meter for a 1/2 second)

14th December 2009, 01:05 AM	#5
nhuwar diyAudio Member Join Date: Jan 2007 Location: Tomball Texas	Whats the rectifier tube and what is the size of the filter?

14th December 2009, 01:06 AM	#6
wicked1 diyAudio Member Join Date: Jan 2008	5u4g clc 20uf-6h/150ma-180uf

14th December 2009, 01:12 AM	#7
wicked1 diyAudio Member Join Date: Jan 2008	One thing I failed to mention in the other thread about this, is that I have a negative supply coming off the same 2ndary of the power tx. That goes through a couple of diodes and 100uf-R(forget what)-100uf. Maybe those charging quickly is causing or helping the surge. Well, it doesn't matter. I know the design of the amp is good (it's a tubelab SE, so there are plenty of them out in the world.. I used default values for everything). I think my power tx or choke are somehow causing it. They are literally the only components that haven't been replaced. (well I didn't replace every resistor, but I did test them while trying to solve this issue)

14th December 2009, 01:13 AM	#8
nhuwar diyAudio Member Join Date: Jan 2007 Location: Tomball Texas	Well that seem fine to me. Maybe one of the more experienced can chime in and give you more help then I. Nick

14th December 2009, 03:34 PM	#10
wicked1 diyAudio Member Join Date: Jan 2008	I have, and I got no sparks (But, I don't always get sparks even with the normal capacitance). I left it like that for several days, maybe 10 power cycles, and it seemed fine. But otherwise the choke tests fine (has the DCR it should), and seems to function properly after the initial surge. My power TX is a hammond, and has never been right.. It's supposed to be 250-0-250, but I get about 300-0-300 out of it! Even under full load, it's putting out way more power than it should. So, it's definitely a suspect too. I hope the problem is just the initial surge, and I have some cl-90's on the way to hopefully fix that. Once I have some extra money, I guess I'll purchase a new power tx and choke.. Then I will have replaced every single component in this amp.. (always w/ better parts, so Im not complaining)

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