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He there,Both my GE6550 exhibit some blue glow inside when warmed up. Is this a common/normal thing, or i this the first sign of ageing? I bought them last December from Billington in England. B+ is 540 VDC, triode mode, Dyna Mk3, separate cathode resistors 15 ohms, cathode voltage 0,8 VDC each.
I'd be grateful for an explanation
DynaMite
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Check the bias on the power tubes - letting to much current pass will cause that blue glow too - that coupled with a poor vacuum will cause it. Sounds like the tubes are pushed to the max.
> > letting to much current pass will cause that blue glow too - that coupled with a poor vacuum will cause it. Sounds like the tubes are pushed to the maxHuh? I've never heard that before. It was my impression that tubes that glowed actually tended to have better vacuums. On my OTL amp, a few tubes glow out of 10 and others don't. They're pushed the same. I also find it very common with old 45s. I like it, it looks cool in the dark.
Yep, that's what most say, but I have read that impurities in the vacuum are stuck by electrons (ions?) and excited and start to glow. Makes sense to me. If it were a true, pure vacuum, it would not glow.Achieving a pure vacuum is difficult in the manufacturing process.
True, even now, getting a perfect vacuum is impossible. I'm don't know about impurities, but it could definately relate to the materials used in older tubes along with the gas that was used to purge the air during the vacuum process.
Both are right.When there is blue glow outside the plates, aroud the glass - this is electron bombardment and usually indicates a very good vacuum. My 350B's in my main monoblocks exhibit this, and they always did - and they have been running fine for years. A good sign & great to look at, perfectly safe.
But when there is blue glow inside the plates, around the anodes - this indicates poor vacuum and a gassy tube. This is a problem. For example, I have a very old Arcturus 180, that on turn-on fills with intense blue light from the anodes, virtually lighting up the entire top of the bottle bright as a lightbulb, settling down after a minute or so, to a blue glow just inside the plates. Obviously, this is a problem tube with severe gassiness, it is quite unsafe to use as..well...that gas could very well blow.
As to the state of vacuums, there are no perfect vacuums, not even outer space - there are several scientific studies, beyond my comprehension, that suggest the vacuum in the universe is decaying over time. But a long, long time. Such is the way with tubes also, the vacuums are decaying on all NOS tubes, the only issue is at what rate, and is this rate even relevant yet.
Yes, you are right about the bombardment, but the blue glow on the electrode structure is perfectly normal and the gentle blue glow near the glass is due to the collision of ionized gas molecules with the glass - usually indicating a soft tube. Valves during manufacture have the air pumped out of them and any remaining gas is removed by the getter. Try reducing the negative bias on a tube and you will start to see this blue glow - even on hard (good vacuum) tubes. All tubes have gas to a certain degree - some glow, some don't for the same type tube.
The GE 6550A's are my favorite tube to show off the guests at night, in My Jolida 502A. All 4 have a nice blue glow all around the inside/outside of the glass. Perhaps impurities in the glass?This is a new quad with about 100 hours, a select quad with "Jadis" in Gold lettering. Sound great, look great.
WE300B has the same effect in my DIY HIF Billie's, but not as dramatic as the GE 6550A's.
I don't exactly buy it. I certainly don't buy the seagull thing. I have some 8417's that glow around the glass, and a 3D21B that has a lot less. All ov them sound briliant and have done this since I first plugged tham in. 3D21's were new, and still perform just like when I plugged them in. This in only the surface fo the glass envelope that has the blue fire around it in some semi-random pattern.
regards,
Douglas
Hi,A little blue glow aroung the surpressor grid isn't that a deal (often, sometimes it can be a major thing :-) ).
I have two Tele El34 running for over two years now with a little blue glow around the outer grids.
I also have tubes with blue glow at the glass and those could be used to throw at seagulls (or whatever except for using in a curcuit).
Don't throw them at seagulls :-) there's nothing wrong with them. Glass can fluoresce, but it isn't harmful.
Hi,Okey...
But seagulls are mos annoying!
!!!!!
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