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MV rectifier cloud flicker

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Posted on February 7, 2017 at 14:05:25
aknaydenov
Audiophile

Posts: 106
Location: Sofia, Bulgaria
Joined: September 13, 2015
Hello,

I recently installed MV rectifiers (DCG4/1000 RTC) on my SET monblocks. I'm very happy from their performance, although there is something that makes me wonder...

The ionized mercury (blue cloud) sometimes starts to flicker at low random frequencies, ranging from 1 to 10Hz, non-periodically, slightly. This happens from tube to tube. Sometimes one rectifiers stops flickering, but another begins.
A problem is, it is invisible to the camera, but visible to the human eye.

Can anyone tell me, any mechanism of the reason it happens and should I be worrying about it?
The current draw should be constant (100mA), because it's a SET amplifier. The flickering is independent of any music.

Best regards,
Alexander.

 

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How long did you run them in before hitting them with high voltage?, posted on February 7, 2017 at 18:20:49
Chip647
Audiophile

Posts: 1658
Location: The South
Joined: December 24, 2012
Old Mercury Vapor tubes should be run with the filament but no high voltage for a number of hours before using. The mercury in old stored and shipped tubes is splattered all over the tube, on the plates and filament where it does not belong. Mercury is a pretty good conductor and should not be where it is not supposed to be.

 

RE: How long did you run them in before hitting them with high voltage?, posted on February 9, 2017 at 11:34:19
benie
Audiophile

Posts: 1848
Location: Alberta, Canada
Joined: October 24, 2004
If you look at most MV rectifier tube data, they will say 20-30 min warm up before applying high voltage for new tubes or tubes that have not in use for a while.
When the tubes warm up the Mercury will settle at the bottom, at any time when a tube has been on it side, one must go through the warm up procedure again

 

RE: How long did you run them in before hitting them with high voltage?, posted on February 10, 2017 at 15:06:59
aknaydenov
Audiophile

Posts: 106
Location: Sofia, Bulgaria
Joined: September 13, 2015
Hello,

I was theoretically very prepared before using the rectifiers. I did prewarm them for 30 minutes, observing the mercury vaporizing from the cathode and anode, and depositing to the bottom of the glass.

The rectifiers work fine. I was just curious about the random cloud flicker I have from random tubes at random times. Maybe it is the way they should work? I'm curious behind the physics behind it.

 

RE: How long did you run them in before hitting them with high voltage?, posted on February 10, 2017 at 18:41:33
benie
Audiophile

Posts: 1848
Location: Alberta, Canada
Joined: October 24, 2004
Well I do know when more current is needed the tubes will light up a lot more blue. When I use them on my headphone amp, they glow much brighter then on my Preamp.
I have seen on you tube where some old theather amps with MV tubes are glowing bright then lower then brighter again. like the tubes are dancing to the music

I think it happens when some good musical peaks happen as you said when some real lows freg. I won't worry about it.
Just so you know the globe 866 tubes seem to sound more musical, except for Unighted brand, they suck. RCA one are very nice.

I like your diffusers panels in your room.

 

RE: How long did you run them in before hitting them with high voltage?, posted on February 24, 2017 at 04:19:10
PakProtector
Audiophile

Posts: 11273
Joined: May 14, 2002
I have 866's in my 6CB5A amps. The filter is single stage L-C, and there is a big flash when the plate transformer gets power to its primary. They are Class A, PP so there is no variability to the observed glow...though selecting tubes with a larger shield to anode gap leaves a bit more of the blue cream floating around in the envelope...:) I would love to find some un-shielded globes.
cheers,
Douglas

Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.

 

RE: How long did you run them in before hitting them with high voltage?, posted on February 24, 2017 at 19:05:27
benie
Audiophile

Posts: 1848
Location: Alberta, Canada
Joined: October 24, 2004
When I first put new to me MV tubes in my system, I run them for about 30 min. Then I hit the high voltage switch to light them up. Yes the ones that are shielded show less glow.
But keep your eyes open for the earlier 866 tubes with no shield, sometimes on eBay or some tube dealers, they really have that beautiful full blue glow.
I just got some ( in the mail ) nice early 872 tubes with no shield, as well I have an early Deforest type 872 tube with no shield and they are very sweet.

Also addind a choke to the the plate of the 866 tubes does 2 things, it makes sure they each get the same current, also the best thing is the sound quality improvement with the choke on the plate. With the 866 type tube I have used anywhere from 60 my at at least 500 ma, to 1 h choke. The triad 320 my at 500 ma does a very nice job and are very reasonable cost.
A very good improvement with the choke on the plate.

 

RE: How long did you run them in before hitting them with high voltage?, posted on March 4, 2017 at 05:28:11
PakProtector
Audiophile

Posts: 11273
Joined: May 14, 2002
I had only one failure. It was a Taylor glob, and I ran heater power for an hour. When I ran AC through it, cathode coating would get blown off in little sparks. Not sure what had happened; by the time an hour was up, the bottom of the envelope was goated in Hg, and the rest of the glass was clear...
cheers,
Douglas

Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.

 

RE: How long did you run them in before hitting them with high voltage?, posted on March 4, 2017 at 13:00:57
benie
Audiophile

Posts: 1848
Location: Alberta, Canada
Joined: October 24, 2004
I have had a number of rectifiers that the cathode coating came off. But they still worked well afterwards. I have a number of 249C tubes like this.

 

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