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'Indigo tubes? (12DW7 )'
Author:ogorir (registered user: 1700 posts )
Date: Sat, Jan 26th, 2008 @ 16:40 ( . )

i just changed around the reverb driver in my twin (again) so I could use a 12DW7[1].

Before I fired it up, I decided to test that DW7 in the V1 of my clean preamp[2]and... theres a nice indigo glow coming from inside the plates. Obviously that tube has a bit of a gas issue. It looks damn cool though.

so, I guess I'm changing that Rp back to a 22k and using a 12au7 until I buy a new DW7.

[1]it had 1/2 12au7 as the reverb driver[3], the other half was a post tonestack makeup stage after the blues input. it didn't have enough nuts to drive the PI (it sounded good on 10 through 4 6l6s). unfortunately, the reverb driver was on the 12ax7 side of a dw7, so I had to swap everything from one section to the other.

[2]it had 1/2 12au7 as the reverb driver, the other half was a post tonestack makeup stage after the blues input. it didn't have enough nuts to drive the PI. unfortunately, the reverb driver was on the 12ax7 side of a dw7, so I had to swap everything from one section to the other.)

[3]I did have a BH7 in as the reverb driver/makeup stage, but it was drawing too much current and dropping b+ too much , so I decided to give an AU7 a try. it sounds even better than the BH7, which is a lot better than the parallel AT7. it gets all of the reverb volume, but it doesn't 'quack' if you hit a string hard. It sounds a lot smoother and more natural.

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'Indigo tubes? (12DW7 )'
Author:LeeMo (registered user: 196 posts )
Date: Sat, Jan 26th, 2008 @ 20:09 ( . )

I thought that blue glow was a normal thing.

[link]


LeeMo


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'Indigo tubes? (12DW7 )'
Author:ogorir (registered user: 1700 posts )
Date: Sat, Jan 26th, 2008 @ 20:47 ( . )

it depends on where the glow is. glow inside the plate structure is bad(sometimes), glow clinging to the glass is normal (and cool).

the glow inside the plate structure are gasses ionizing when current passes through them from the cathode to the plate, whereas blue glow on the glass is low energy secondary emission from the glass.
that article says this is from stuff boiling off the cathode. thats still gas, and the purpose of the getter is to absorb that. there is a big dark thin spot in the getter and this is a pulled tube, leading me to believe that its at its end of life and starting to get gassy.


I have a few power tubes that have glass glow that work fine and 2 known gassy tubes that have inner plate glow that is indigo, not blue.

the color irks me, it doesn't look normal.
you can't see the filament glowing through it.

I'm correlating a bit, I haven't the resources to test who's right for sure, but I'm inclined not to use a preamp tube with a violent indigo glow coming out of the plate structure.

I also tend to distrust unsubstantiated 'facts' floating around the internet, especially when relating to tubes and other such 'mojo' items.


anyhoo, I'm fine with the 12AU7 in there now that i changed the plate resistor for a 22k. i had the 10k from the 12BH7 in there, and that wasn't cutting the mustard with the squish pot turned to full squish and the tone stack in, but now it seems to be doing alright.


just the tonestack left to tweak and this thing can go back together

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'Indigo tubes? (12DW7 )'
Author:Miles O'Neal (registered user: 13998 posts )
Date: Sun, Jan 27th, 2008 @ 16:56 ( . )

Larry (the Blue Glow FAQ guy) used to hang out on AGA a lot before it turned into a big cesspool[1]. He definitely knows his stuff. He used to go by Dr. Nuketopia, or just Nuke, on newsgroups, so you can search for yourself to verify his creds, but if it's worth anyhting, I vouch for his knowing whereof he speaks. Great guy, and also knows what he doesn't know, and will freely admit it.


[1] Though lately the S/N is better than it has been for some time

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'Indigo tubes? (12DW7 )'
Author:ogorir (registered user: 1700 posts )
Date: Tue, Jan 29th, 2008 @ 12:45 ( . )

well, I was right. i put it in V2 of the clean amp (which happens to have the sections arranged (atleast in my layout) so the au7 half is the cathode follower and...

it threw large blue balls of plasma[1] around the bottom of the tube in a very impressive display when B+ was applied. it made that 12au7 in that firefly clip look silly. I'm going to try to see if i can find a video camera and repeat it.

anyway, indigo/blue glow coming from inside the plates in preamp tubes is BAD!

it describe accurately how it looked(pre failure), it was if the whole inside of the plate structure had been filled with blueish purple goo. it was not clinging, it was not subtle. you couldn't see the cathode through it from the bottom. if you see this behavior, turn your amp off and get a new tube.

[1] it probably wasn't actually plasma, just ionized gasses boiling off the electrodes, but hey :)

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'Indigo tubes? (12DW7 )'
Author:Miles O'Neal (registered user: 13998 posts )
Date: Wed, Jan 30th, 2008 @ 00:28 ( . )

Wow1 I hope you can video that. I'd love to see it.

My assumption is that blue glow from the bowels of the tube (or my bowels for that matter) is a Bad Thing.

Blue glow around the glass, however, I love.

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'Indigo tubes? (12DW7 )'
Author:ogorir (registered user: 1700 posts )
Date: Wed, Jan 30th, 2008 @ 00:51 ( . )

thats sortof what i was trying to get across. glow from inside the plate structure is a BAD thing.

there are two blue patches where the holes in the plates are on my 12BZ7 project onto the glass and they dance around a bit when you hit them hard.

also, the best sounding power tube I've got has got quite a bit of blue clinging to the glass that goes away when you play over say a third volume. I don't really understand why the glow goes away, its a single ended amp. the plate voltage doesn't appreciably dip.



until i find a camera, here is a brief description of what happened. i flipped the power on, let the tubes heat up. this DW7 always had a dull heater, but i think it may have opened (also contributing to the show). but, this looked pretty much the same as the last time i plugged it in (albeit in the first socket) so i gave it a go and flipped the standby.

of course, i had my face about a foot away from the tube trying to see of the heater was on, so it scared the piss out of me when a pair of blue ionized gas balls flew out of the bottoms of the plates and circled around the bottom of the tube. it made a crackly noise, and that was about the time i flipped the standby back off.

it looked a lot like ball lightning, really. it was probably the coolest thing I've done in a long time. I'm really hoping it was an open heater and this can be repeated with other junk tubes, or perhaps sustained for a period of time. it would make a very impressive display.

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