Hmm… not much real explanation what the purpose of the graphite layer is so far.
Let’s face it, those tubes were designed and produced for serious duty, at days audiophile fashion was NOT in view at all. So it has no cosmetic purpose at all but it is there on serious engineering grounds.
Concerning JAN and MIL spec., yes often these are the same devices as the civil ones. However they are often burned in at the factory and are tested much more rigorously according to military protocols and often to much closer tolerances. This to minimize the risk of premature failures.
Cheers 😉
Let’s face it, those tubes were designed and produced for serious duty, at days audiophile fashion was NOT in view at all. So it has no cosmetic purpose at all but it is there on serious engineering grounds.
Concerning JAN and MIL spec., yes often these are the same devices as the civil ones. However they are often burned in at the factory and are tested much more rigorously according to military protocols and often to much closer tolerances. This to minimize the risk of premature failures.
Cheers 😉
Sch3mat1c said:
fdegrove said:
Uhmmm.... lay off the pipe, Frank. First you said "blue glow is bad and such tubes should be disposed of". My rebuttal is above. Now you say you're still right, even though you cite references contrary to your point of view!!? 😕 😕
Heh, I was right in the first place, whaddya know.
Tim
Interesting bit about tubes etc. I thought blue colour was stray hydrogen from anode outgassing.
In my amps I drive them hard so that the output stage behaviour is more linearised for lowest THD. With sep bias adjust resistors this works very well.
In my dual switchable UL 25/150W amp; with 250V B+ I run 6550's/KT88's each 85mA (almost class A), and 485V B+ in AB2 at 70mA each. Doing this will get 2nd/3rd harm'c THD down to 0,05% at 25/120W@1Khz. You will only get these figures with careful layout and stabilised HT supplies. The nice thing is that I use only 20bB NFB to knock S/N down to -75bBu (ref 0dBu).
I am very content at that.
more anon
rich
In my amps I drive them hard so that the output stage behaviour is more linearised for lowest THD. With sep bias adjust resistors this works very well.
In my dual switchable UL 25/150W amp; with 250V B+ I run 6550's/KT88's each 85mA (almost class A), and 485V B+ in AB2 at 70mA each. Doing this will get 2nd/3rd harm'c THD down to 0,05% at 25/120W@1Khz. You will only get these figures with careful layout and stabilised HT supplies. The nice thing is that I use only 20bB NFB to knock S/N down to -75bBu (ref 0dBu).
I am very content at that.
more anon
rich
Hi,
Tim,
I didn't say that. Here's what I said:
Note the : "can be".
The key is to know what and where the blue glow is in the tubes.
Also, a tube that didn't show that blue glow when new but develops it after use is at least a candidate for a gasleak test on the meter.
This is more in line with my experience:
KR
Cheers,😉
Tim,
I didn't say that. Here's what I said:
Note the : "can be".
The key is to know what and where the blue glow is in the tubes.
Also, a tube that didn't show that blue glow when new but develops it after use is at least a candidate for a gasleak test on the meter.
This is more in line with my experience:
KR
Cheers,😉
Sorry Frank, but I cannot take that KR site that serious. It’s a lot merchandising talk. What they say about mesh anodes is not in agreement with old textbooks. Also they state that a NEGATIVE charge is build up on the glass. All old textbooks about the physics of vacuum electron devices state that the secondary emission from the glass leaves a POSITIVE charge. The secondary electrons are attracted and drained by the high voltage on the anode until there is balance between the voltage on the glass and the anode. Then the secondary electrons are causing excessive noise and one book states that this can be severe.
The carbon coating has a porous structure. Electrons escaped from the tube system are heavily braked in this labyrinth of carbon crystals and loose most of their energy so they cannot generate secondary electrons. Carbon itself has quite a low secondary emission factor. For this reason anodes are sometimes also coated with carbon.
Cheers 😉
The carbon coating has a porous structure. Electrons escaped from the tube system are heavily braked in this labyrinth of carbon crystals and loose most of their energy so they cannot generate secondary electrons. Carbon itself has quite a low secondary emission factor. For this reason anodes are sometimes also coated with carbon.
Cheers 😉
Hi,
Neither do I.
It's just that what Krone says about the blue glow makes alot more sense to me even when he overstates the importance of high vacuum.
Too high a vacuum and the tube won't have any useful life.
Back OT, the carbon coating is interesting and if it actually works as stated and yields better audio tubes then I wonder why they gave it up or why it's not reintroduced.
In one of the first replies to the question I said it was put on to reduce the effect of impurities in the glass that cause secondary emission.
These impurities where much reduced later on by improved baking techniques.
IMO, this is the reason why the coating technique was abandoned.
I wouldn't know but their conclusion that it would be preferable not to have that blue glow makes sense to me.
BTW, if you watch closely while playing music you can see it modulated by the music: it's actually dancing about.
Kind of like having a mini-disco at home.😎
Cheers,😉
Neither do I.
It's just that what Krone says about the blue glow makes alot more sense to me even when he overstates the importance of high vacuum.
Too high a vacuum and the tube won't have any useful life.
Back OT, the carbon coating is interesting and if it actually works as stated and yields better audio tubes then I wonder why they gave it up or why it's not reintroduced.
In one of the first replies to the question I said it was put on to reduce the effect of impurities in the glass that cause secondary emission.
These impurities where much reduced later on by improved baking techniques.
IMO, this is the reason why the coating technique was abandoned.
I wouldn't know but their conclusion that it would be preferable not to have that blue glow makes sense to me.
BTW, if you watch closely while playing music you can see it modulated by the music: it's actually dancing about.
Kind of like having a mini-disco at home.😎
Cheers,😉
If you can get a 6L6 or sim to glow, I'm going to throw the towel in........I've been using the same pair of 807's (Ken Rad written on base) for years and they glow a lovely and uniform blue. The 5U4 (also Ken Rad) behaves the same and they make a centre discussion piece. Irradiated I might be; there is one divine factor in this amp and it's 600V B+. After so many years service I don't think the electric blue an indicator of imment failure. No other tube had been produced in such massive quantities as 807's.
Great tube except for that ruddy top cap and UX5 base.
rich
Great tube except for that ruddy top cap and UX5 base.
rich
Wholly electrons, Batman!
If electrons accelerated towards the anode miss, and strike the glass, a negative charge builds up on the inside of the glass. The collision and consequent deceleration can cause a glow. Because the glass is an insulator, there is nowhere for the electrons to go. The (negatively charged) electrons on the inside weakly repel other electrons, so a balancing positive charge forms on the outside.
Coating the inside of the glass with graphite and connecting it to the cathode provides a discharge path for the electrons. Graphite has secondary emission ratio = 1, so it releases one slow-moving electron when hit by one fast-moving electron, but I don't know the SER for glass.
If a charge builds up on the inside of the glass it modifies the electrostatic field within the valve electrodes and causes distortion. I suspect that graphite coating (which costs money) was stopped when negative feedback became popular. The improvement wrought by the coating in a power valve wasn't all that great...
So, Sch3mat1c, you were almost right in your first post.
If electrons accelerated towards the anode miss, and strike the glass, a negative charge builds up on the inside of the glass. The collision and consequent deceleration can cause a glow. Because the glass is an insulator, there is nowhere for the electrons to go. The (negatively charged) electrons on the inside weakly repel other electrons, so a balancing positive charge forms on the outside.
Coating the inside of the glass with graphite and connecting it to the cathode provides a discharge path for the electrons. Graphite has secondary emission ratio = 1, so it releases one slow-moving electron when hit by one fast-moving electron, but I don't know the SER for glass.
If a charge builds up on the inside of the glass it modifies the electrostatic field within the valve electrodes and causes distortion. I suspect that graphite coating (which costs money) was stopped when negative feedback became popular. The improvement wrought by the coating in a power valve wasn't all that great...
So, Sch3mat1c, you were almost right in your first post.
Hi,
On alot of older valves I can't see a connection between the coating and the cathode; just a band of coating covering about a third of the height of the glass.
You don't seem to think the fact that with older valves the glass wasn't baked properly played a role or am I misreading you?
If the coating serves to neutralise the static charge of the glass itself a simple dot of graphite can do wonders already.
That's a technique used in RF/VHF to neutralise static charges of capacitor plastic casings, BTW.
Also something I use succesfully on coupling caps with plastic wrappers or cables with plastic jackets.
Cheers,😉
On alot of older valves I can't see a connection between the coating and the cathode; just a band of coating covering about a third of the height of the glass.
You don't seem to think the fact that with older valves the glass wasn't baked properly played a role or am I misreading you?
If the coating serves to neutralise the static charge of the glass itself a simple dot of graphite can do wonders already.
That's a technique used in RF/VHF to neutralise static charges of capacitor plastic casings, BTW.
Also something I use succesfully on coupling caps with plastic wrappers or cables with plastic jackets.
Cheers,😉
Newsflash! Carbon dating: Electrons attracted to graphite
Agreed, I can't see a connection either, but I'm not about to sacrifice my graphited valves to science (smash 'em) to check the point.
I don't think it's down to the glass, after all, if it were, you would expect the effect to be strongly temperature dependent, yet small-signal valves have the treatment too.
I'm wondering about your dot of graphite on capacitor casings. Can you elaborate?
Agreed, I can't see a connection either, but I'm not about to sacrifice my graphited valves to science (smash 'em) to check the point.
I don't think it's down to the glass, after all, if it were, you would expect the effect to be strongly temperature dependent, yet small-signal valves have the treatment too.
I'm wondering about your dot of graphite on capacitor casings. Can you elaborate?
Hi,
Heaven forbid, no.
Could be checked on a dead one though...Just cut the glass at the base and see if there's a downward connection.
Somehow I doubt there ever was any.
Not that I'm an expert on this but I've seen many HV pulse caps (usually paper/metallised whatever) that had a dot of graphite paint on the outside to reduce/kill any static charge left on the casing.
At least that's what I understood of it.
The same technique is used on CRT screens, or so I've been told.
I'm not sure if you were a member yet at that time but Ed Goey ( a Dutchman) and myself have discussed the merits of Superblack (a JVC spin-off product originally developped for CRTs).
The product was discussed in "L'Audiophile" and briefly offered by their shop, "La Maison de L'Audiophile".
Between you and me, it's no different from any graphite spray you can buy in any electronics shops.
Maybe it had a higher concentration of graphite particles, not sure here.
When applied to low level circuits it does bring more micro detail and it cost almost nothing.
It works fine on semi-conductors with plastic casing and resistor a la Vishay S102 as well.
Somehow it reminded me of that Tubeolator product...Remember that one?
Only saw that on RF pentodes though and than the entire inside of the glass was covered with it.
Can't say I ever saw it on a triode...Haven't seen evrything either.
Cheers,😉
Heaven forbid, no.
Could be checked on a dead one though...Just cut the glass at the base and see if there's a downward connection.
Somehow I doubt there ever was any.
Not that I'm an expert on this but I've seen many HV pulse caps (usually paper/metallised whatever) that had a dot of graphite paint on the outside to reduce/kill any static charge left on the casing.
At least that's what I understood of it.
The same technique is used on CRT screens, or so I've been told.
I'm not sure if you were a member yet at that time but Ed Goey ( a Dutchman) and myself have discussed the merits of Superblack (a JVC spin-off product originally developped for CRTs).
The product was discussed in "L'Audiophile" and briefly offered by their shop, "La Maison de L'Audiophile".
Between you and me, it's no different from any graphite spray you can buy in any electronics shops.
Maybe it had a higher concentration of graphite particles, not sure here.
When applied to low level circuits it does bring more micro detail and it cost almost nothing.
It works fine on semi-conductors with plastic casing and resistor a la Vishay S102 as well.
Somehow it reminded me of that Tubeolator product...Remember that one?
Only saw that on RF pentodes though and than the entire inside of the glass was covered with it.
Can't say I ever saw it on a triode...Haven't seen evrything either.
Cheers,😉
Unfortunately, I don't have many graphited envelopes, and the ones I do have are all goers - some are 6SN7, so you can understand my reluctance to sacrifice them.
CRTs have an outer coating of colloidal graphite. The final anode is a conductive coating sprayed over the inside of the tube, so the two form a glass dielectric capacitor. Admittedly, it's quite a low capacitance, but it's smoothing 15.625kHz, and the current is very small, so the effect is significant. Or, to put it another way, when a trainee decided to clean up the "nasty, dirty" CRT, it didn't work properly any more...
I'm afraid that the thought of coating a semiconductor with colloidal graphite and adding leakage paths makes me cringe.
CRTs have an outer coating of colloidal graphite. The final anode is a conductive coating sprayed over the inside of the tube, so the two form a glass dielectric capacitor. Admittedly, it's quite a low capacitance, but it's smoothing 15.625kHz, and the current is very small, so the effect is significant. Or, to put it another way, when a trainee decided to clean up the "nasty, dirty" CRT, it didn't work properly any more...
I'm afraid that the thought of coating a semiconductor with colloidal graphite and adding leakage paths makes me cringe.
Hi,
Yes, understood.
It seems to work fine though...Never seen these FKP caps with a black graphite dot on the outer casing? Or a justification?
Years ago chief engineer Fransen of Roederstein Belgium explained it to me: it counters surface charges held in plastics.
I took his word for it and it appeared to work...It's just as plausible as the graphite coating to me.
Nowadays some people go one step beyond and remove plastic wherever they can and report stunning results...
Trying never hurt anyone, 😉
Yes, understood.
It seems to work fine though...Never seen these FKP caps with a black graphite dot on the outer casing? Or a justification?
Years ago chief engineer Fransen of Roederstein Belgium explained it to me: it counters surface charges held in plastics.
I took his word for it and it appeared to work...It's just as plausible as the graphite coating to me.
Nowadays some people go one step beyond and remove plastic wherever they can and report stunning results...
Trying never hurt anyone, 😉
> Too high a vacuum and the tube won't have any useful life.
There is no such thing as a vacuum "too high" for a thermionic vacuum tube. Ideally there would be absolutely no stray gas.
In real life, tubes have to be pumped and baked for hours just to get a "good enough" vacuum.
There are two main types of tube glows (not counting the obvious heater glow):
Violet on the inside of the glass or sometimes on the tips of the elements. This is neither good nor bad for the tube.
Various colors between tube elements. This is bad: it means the tube is gassy and the electron flow is smacking into gas molecules instead of running free. The smacked molecules release heavy positive ions which cause total current to increase and also bombard the cathode.
Another way to check for gas is to connect the tube in-circuit with a switchable grid resistor (just a jumper-wire across the existing grid resistor). If there is significant change in grid voltage or cathode current with a low- or high-value grid resistor, the tube is gassy and liable to run-away. (Exception: low-voltage preamp triodes often did use over-sized grid resistors and normally ran small grid leakage; check these with book-value grid resistor, usually 1Meg, versus zero-ohm grid resistor.)
> you can see it modulated by the music:
Unless you have actually struck a gas-discharge (which is usually instant-death in thermionic equipment), a "dancing glow" is always harmless. Gas-glow tends to be constant (or increases rapidly to tube death).
Carbon coating: while it may help equalize charges, the real reason is because in the 1930s, people were annoyed by tube glow and wanted less of it (hard to believe today). A shot of dag inside the bulb costs almost nothing, hides the glow, adds very little to the pumping load.
There is no such thing as a vacuum "too high" for a thermionic vacuum tube. Ideally there would be absolutely no stray gas.
In real life, tubes have to be pumped and baked for hours just to get a "good enough" vacuum.
There are two main types of tube glows (not counting the obvious heater glow):
Violet on the inside of the glass or sometimes on the tips of the elements. This is neither good nor bad for the tube.
Various colors between tube elements. This is bad: it means the tube is gassy and the electron flow is smacking into gas molecules instead of running free. The smacked molecules release heavy positive ions which cause total current to increase and also bombard the cathode.
Another way to check for gas is to connect the tube in-circuit with a switchable grid resistor (just a jumper-wire across the existing grid resistor). If there is significant change in grid voltage or cathode current with a low- or high-value grid resistor, the tube is gassy and liable to run-away. (Exception: low-voltage preamp triodes often did use over-sized grid resistors and normally ran small grid leakage; check these with book-value grid resistor, usually 1Meg, versus zero-ohm grid resistor.)
> you can see it modulated by the music:
Unless you have actually struck a gas-discharge (which is usually instant-death in thermionic equipment), a "dancing glow" is always harmless. Gas-glow tends to be constant (or increases rapidly to tube death).
Carbon coating: while it may help equalize charges, the real reason is because in the 1930s, people were annoyed by tube glow and wanted less of it (hard to believe today). A shot of dag inside the bulb costs almost nothing, hides the glow, adds very little to the pumping load.
Hi,
According to what was published by Audio & Techniek "Audio Discussions #4" in 1991 after a talk with, amongst others, ex-Philips engineer Mr. N.E. van Mossevelde there is a point where when the vacuum is too high the tube will be hyperactive and shorten it's own life due to excessive bombardment of the cathode.
A member of this forum, Guido Tent, participated in this get together held at Mr. Ed de Jong's place.
On my own initiative in the status of distributor of electron tubes, I checked further with Richardson Electronics, Thomson CSF and Thales and they all confirmed this.
If you have proof to the contrary, I'd like to hear it.
Cheers,😉
According to what was published by Audio & Techniek "Audio Discussions #4" in 1991 after a talk with, amongst others, ex-Philips engineer Mr. N.E. van Mossevelde there is a point where when the vacuum is too high the tube will be hyperactive and shorten it's own life due to excessive bombardment of the cathode.
A member of this forum, Guido Tent, participated in this get together held at Mr. Ed de Jong's place.
On my own initiative in the status of distributor of electron tubes, I checked further with Richardson Electronics, Thomson CSF and Thales and they all confirmed this.
If you have proof to the contrary, I'd like to hear it.
Cheers,😉
He's full of it. "Excessive bombardment" must mean electrons, as with a high vacuum there is no gas to ionize. But that is completely harmless, as it's incident to the operation of a magnetron, and AFAIK those have the same lifetimes as normal amplifier tubes.
Tim
Tim
Crap Will Hit The Fan...
Hi,
What else?
Congratulations. And what's the MTBF of a vacuum tube exactly?
Cheers,😉
Hi,
What else?
Congratulations. And what's the MTBF of a vacuum tube exactly?
Cheers,😉
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