Getter used up but tube is fine.

[sKiZo]

Long as we're not on the subject ... <G>

The Gold Lions have a similar "problem". I'd think that all has something to do with the materials used in tube construction. Let's face it - the uber rare minerals used in the older tubes just aren't available anymore, or extremely pricey.

PS - both these and the KT120's (as well as most current production KT88's) have three getters. A lot of the early production "premium" tubes (MOV anyone?) got away with one. I'd also attribute that to production and material issues as the tube designs are otherwise similar.

Oh. And foil getters always sound better.
(Let the carnage begin) ;-}

 

[Retrovert]

No rare elements are or were used in tubes. Not even uncommon ones. Alkali metals are among the most common elements, and neither tungsten nor nickel is in short supply. Labor cost has always been the dominating factor in tube cost and loss of old tooling and cost of new machinery has limited new manufacturing efforts. I am, of course, ignoring specialty items like gold-plated grids, but even those have little gold.

Large getters pose an issue because the evaporated metal must not contact internal structures. Avoiding collateral damage determines the getter position and size. Multiple getters are not better or worse in terms of function or sound, only in terms of side effects.

The sole purpose of the getter is to remove residual gas. It has zero effect on sound. The only correlation, not causation, in play is that better designed tubes sound better, and such tubes may have also had bettter designed getters. But the getter itself has zero effect on sound, other than to improve tube function by consuming residual gas which would affect performance.

 

[sKiZo]

A subgroup of the rare-earth metals, consisting of those with atomic numbers between 57 and 63 and ytterbium, is often called the cerium metals. Misch metal is an alloy of the cerium metals often used in lighter flints, in alloys with other metals (especially magnesium), and to remove residual gases in the manufacture of vacuum tubes.

http://www.encyclopedia.com/science...stry/compounds-and-elements/rare-earth-metals

I do have doubts when it comes to the "Chinese monopoly" on rare earth metals mentioned by some. Yes, they have made a concerted effort in the recent past to corner the market (and drive up prices), but there's still a LOT of these elements available elsewhere. Just a whole lot harder to get to ...

 

[maxhifi]

 

[Retrovert]

Rare earths are not "rare" except in relative proportions. This misnomer confuses people. Rare earths are common enough.

Tube cost and manufacturability are not limited by cerium, nor is the tube price dependent upon it.

Getters are made, aside from ones using tantalum, from common elements. No magick there. Tantalum, like cobalt, is a conflict mineral, and has other issues with price, supply, and human suffering.

 

[Retrovert]

Max, that laundry list does not indicate most of the less-common elements are only used in trace amounts. So while true, it is misleading.

 

[Retrovert]

One more thing. The Chinese were taken to the cleaners trying to create a rare-earth monopoly. Artificially low prices to keep others out of a market is not forever sustainable. Well, aside from Amazon, of course. And even Amazon exacts price concessions from suppliers to keep prices low.

 

[maxhifi]

Max, that laundry list does not indicate most of the less-common elements are only used in trace amounts. So while true, it is misleading.

Well, that's true. I mostly like it because it's a cool old illustration, I don't think it was intended to be of any real use besides being marketing propaganda, to show people how tubes are fairly complex devices.

 

[Retrovert]

Sure, but the context was tube availability being somehow limited by exotic ingredients, including the getter.

.

 

[maxhifi]

Sure, but the context was tube availability being somehow limited by exotic ingredients, including the getter.

.

I know, I should add some descriptive language. I posted it because it's a supposedly all inclusive list of materials used in the 1940s to make tubes, and nothing jumped out to me as being especially unobtainable., although some are considered hazardous to health these days, and it would make sense to try and engineer them out.

 

[trainbuftony]

I have a theory. If you leave that tube alone it will last forever. It has had every opportunity to fail yet still works, the getter, is but a ghost. Tube doesn't care, tube has a job to do. If it was going to fail it would have already done so. This one is going to take some outside occurrence to finally push it over the edge. When a tube this old finally stops working is it really a failure, or is it called retirement?

 

[jaymanaa]

Seems like 7591s, and 7868s are known for continuing to test good, and work fine with very thin flash remaining. These tubes also have a very special coating on the cathode, so I wonder if that's why? Back in the day, receding getter flash was used as a measuring standard on critical use tubes (elevators for one), and tubes would be replaced after the flash receded to a certain point. Some tubes even came with a line on them to indicate where the getter flash could go to before the tube was replaced. I stay away from 9 pin tubes with worn getter flash.

 

[maxhifi]

Man I've actually seen those elevator control panels with a few tubes in them, I think they were 6SN7s or some kind of thyratron. Watching one of those old electromechanical elevator controllers in a large building work during a busy time of day, is fun, dozens of open frame control relays sparking, away as floors are requested, and the massive cam turning as the elevator goes up and down. Otis really had some imagination when they figured out how to control elevators. I wonder if any of them are still in service, or if they've all been converted to digital.

 

[nj pheonix]

There are probably a few left.
Not too many though.
New ones are easy to maintain.
They just swap boards.
Unless during the updates, someone was stockpiling the old stuff, spares must be awful scarce by now.

 

[maxhifi]

Yeah I suppose they've gone the way of the old telephone exchanges

There are probably a few left.
Not too many though.
New ones are easy to maintain.
They just swap boards.
Unless during the updates, someone was stockpiling the old stuff, spares must be awful scarce by now.

That world moved pretty slow though, due to regulatory constraints and a virtual monopoly by some of the bigger players. I've seen setups from the late 1970s which had large selenium rectifiers in the control circuits, and used a motor/generator set to make DC for the lift motor. Those things were 20 years out of date even when installed, compared to the rest of the electrical industry. Talk about going off-topic, but I find it interesting.

 

[BillWojo]

I have an old Monarch 10EE lathe that uses the same DC drive as the old elevators use. Two huge C16J thyratrons and a bunch of other tubes to control the 3HP DC motor from almost zero speed to it's max speed. Many attempts have been made to replace this system by others with a simple 5HP AC VFD drive but the problem is they have no low speed torque. A 7.5 HP AC VFD drive gets you closer but is still no match for the DC motor.
I have been chasing a problem with this for a long time. Need to get back on it. I could really use this thing.

BillWojo

 

[maxhifi]

I have an old Monarch 10EE lathe that uses the same DC drive as the old elevators use. Two huge C16J thyratrons and a bunch of other tubes to control the 3HP DC motor from almost zero speed to it's max speed. Many attempts have been made to replace this system by others with a simple 5HP AC VFD drive but the problem is they have no low speed torque. A 7.5 HP AC VFD drive gets you closer but is still no match for the DC motor.
I have been chasing a problem with this for a long time. Need to get back on it. I could really use this thing.

BillWojo

It's not trivial to make an AC motor work as well at low speed as a DC motor, but you could do it. Probably more fun just to make it work as is though, power thyratrons which actually work are like living dinosaurs.

 

[sKiZo]

Man I've actually seen those elevator control panels with a few tubes in them, I think they were 6SN7s or some kind of thyratron.

Wouldn't surprise me if the elevator on Big Bang was a tuber ... that's been out of order for ... what ... ten seasons? <G>

 

[jaymanaa]

Man I've actually seen those elevator control panels with a few tubes in them, I think they were 6SN7s or some kind of thyratron. Watching one of those old electromechanical elevator controllers in a large building work during a busy time of day, is fun, dozens of open frame control relays sparking, away as floors are requested, and the massive cam turning as the elevator goes up and down. Otis really had some imagination when they figured out how to control elevators. I wonder if any of them are still in service, or if they've all been converted to digital.

Yeh, it's like ten really good typists gong at it, and will drive you crazy after a while. I remember the doors to the elevator shaks on the roof always had a sign on them that said "Count your jumper wires". guess it could have been bad to leave a jumper in one of those panels, Ha. I have an NOS ST shape tube that has a red line right above the hump and a sticker telling you to replace it when the getter gets above the line.
Back on topic (sorry for the derail), I'd say the tube(s) in the OP are not dependable at all. I doubt f they will cause any damage when they finally wear completely out, so you could run them until you start getting distortion then replace them. I bet you'd be surprised in the difference in sound if you stuck new tubes in. A scope would really show you.

 

[nj pheonix]

Agreed Jay,
I've seen new looking old stock 7591s test for crap and one's with next to no getter test and work fine.
I'm under no dellusions, these (the one's that look like that) are on borrowed time.
Might as well ride them into the ground as Jay said