Some of my 6AG5 tubes have some tiny dark lines around the cylinder section of the glass. Mainly a particular batch of Sylvania tubes. My rca and GE 6ag5 just have clear glass, and so do my chinese 6j3 (modern equivalent) When i look under an LED scope, i can see that its a bunch if tiny black rings on the glass.
Picture of one of the sylvania next to a chinese 6j3 to show what im talking about. Were NoS tubes and they all look like this one, and im pretty sure i've seen dark glass on tubes before.
What is it? I'm having trouble asking google and search correctly apparently.
I also think the sylvania have a nicer sound to them then my GE or RCA. I imagine it wouldn't have anything to do with this. Would it?
Picture of one of the sylvania next to a chinese 6j3 to show what im talking about. Were NoS tubes and they all look like this one, and im pretty sure i've seen dark glass on tubes before.
What is it? I'm having trouble asking google and search correctly apparently.
I also think the sylvania have a nicer sound to them then my GE or RCA. I imagine it wouldn't have anything to do with this. Would it?
This black area is carbonizing applied to the interior of the glass. It's purpose is to reduce secondary emission. These are electrons that escape from the plate area and strike the envelope, causing the glass to become charged. This interferes with the performance of the tube.
Good engineering, but not absolutely necessary, and an added production cost.
Good engineering, but not absolutely necessary, and an added production cost.
That coating is called 'getter' and its purpose is to hold onto any gaseous molecules in the bulb that were not removed because it's prohibitively expensive to get a higher vacuum. It has no effect on tube performance except to keep unwanted molecules & little atoms from interfering with tube performance, usually by causing unwanted leakages. I have this habit of putting 'little' in front of 'atom', for some reason.
I know what a getter is and does, same with the oxide coating above it.
I was talking about the little perfect cylindrical black rings down the length of the cylinder part of the tube. Some have them some dont, mine that have them as well as black plates definitely perform better in audio circuits and produce far less noise when close to them without shields. All vacuum/non gaseous tubes (as far as im aware) have some form of getter/oxide layer arrangement. This, however, has become something i specifically look for in purchasing 6ag5 tubes even though it makes the tube itself uglier. So i was curious what it is/is for. 6AG5 make absolutely incredible audio preamp triodes, they're cheap and widely available in NoS matched pairs, but i've learned you dont want to use 6AG5 in an audio preamp circuit unless they have black plates and these black rings. Almost always too noisy unless you shield them. (im using 6AG5 because i had a ton of them and the data sheets have spec for triode use in class A amplification, so why not?) They sound so much better to my ears then my 12ax/t7 and 6au6 breadboard arrangements ive tinkered with now (it really is a "step back and say WOW" kind of difference), that ive been very keen to try and take time to figure out what it is about these sylvania 6AG5 that is making them perform so nicely for audio.
I put the picture of the 6ag5 next to a 6j3 to specifically show im not talking about the oxide layer lol. I wasn't entirely sure how to properly frame the question or id have been able to figure this out with a google search. DIYaudio is a fairly intimidating place for me most of the time. And im long-winded and easily misunderstood as well. I tend to only post here now if something is genuinely confusing or eluding me and if the search bar here is turning over no simple conclusions.
I was talking about the little perfect cylindrical black rings down the length of the cylinder part of the tube. Some have them some dont, mine that have them as well as black plates definitely perform better in audio circuits and produce far less noise when close to them without shields. All vacuum/non gaseous tubes (as far as im aware) have some form of getter/oxide layer arrangement. This, however, has become something i specifically look for in purchasing 6ag5 tubes even though it makes the tube itself uglier. So i was curious what it is/is for. 6AG5 make absolutely incredible audio preamp triodes, they're cheap and widely available in NoS matched pairs, but i've learned you dont want to use 6AG5 in an audio preamp circuit unless they have black plates and these black rings. Almost always too noisy unless you shield them. (im using 6AG5 because i had a ton of them and the data sheets have spec for triode use in class A amplification, so why not?) They sound so much better to my ears then my 12ax/t7 and 6au6 breadboard arrangements ive tinkered with now (it really is a "step back and say WOW" kind of difference), that ive been very keen to try and take time to figure out what it is about these sylvania 6AG5 that is making them perform so nicely for audio.
I put the picture of the 6ag5 next to a 6j3 to specifically show im not talking about the oxide layer lol. I wasn't entirely sure how to properly frame the question or id have been able to figure this out with a google search. DIYaudio is a fairly intimidating place for me most of the time. And im long-winded and easily misunderstood as well. I tend to only post here now if something is genuinely confusing or eluding me and if the search bar here is turning over no simple conclusions.
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So far it's only been 6ag5 that i've seen it in personally but i dont have a lot of experience with many other varieties. I have seen tubes with this in their glass as a kid inside TV's and radios though somewhere along the lines. I knew it was a thing some tubes had when i first ;laid eyes on these 6ag5 at least. Just never gave it any thought. Lol maybe those TV or radio tubes were these sylvania 6ag5, idk. They are also my only 6AG5 with carbon black plates and these rings both too (i do actually have a couple raytheon pairs with black plates, but clear glass looking through my box). The sylvania sound the best hands down, so just assuming they are just a performance/quality tier above my other 6ag5 examples and may or may not have anything to do with these rings idk, i assumed probably not. It is absolutely something im going to be looking for specifically, at least when buying more 6ag5 though. I like these tubes a lot for audio and prob gonna tinker with them for some time to come. Lot of this black glass sylvania available on ebay. Even in pre matched NoS pairs for next to nothing. They pretty much plug and play into any circuit a 6au6 will thrive in. 12au6 circuits if you wire the 6ag5 heaters in series, and out perform them both handily. I prefer their soundstage to 12ax7 for sure so far, but dont have a lot of tinkering done there yet, 6ag5 do seem to perform admirably while being far far less picky over the actual operational parameters of a given circuit then 12ax7, in a very "jack of all" kinda way for me so far. This seems to apply to the clear 6ag5 and even the 6j3 too, so long as i shield them well.
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The colour of the plates is not related to the carbonizing applied to the interior of the glass. Also, there has never been any consistency re this treatment. Some tube types have it, some do not, even the same type from the same manufacturer.
If you really want the technical story, it starts on page 439;
https://ia801507.us.archive.org/8/items/in.ernet.dli.2015.205617/2015.205617.Fundamentals-Of.pdf
If you really want the technical story, it starts on page 439;
https://ia801507.us.archive.org/8/items/in.ernet.dli.2015.205617/2015.205617.Fundamentals-Of.pdf
like i said, i didnt think they were related, nor that they'd have anything to do with the sylvanias sounding better, that being said its still something im looking for window shopping for more simply because it's the only common denominator on the 6ag5 i have that sound best to my ears.
I actually assumed they were carbon rings. And i only said "ok so like the plates" in reference to them both being treated in some way with carbon.
This is why DIYaudio is intimidating to me. Im way too long winded for people's willingness to read and be patient today
Thank you for the link
I actually assumed they were carbon rings. And i only said "ok so like the plates" in reference to them both being treated in some way with carbon.
This is why DIYaudio is intimidating to me. Im way too long winded for people's willingness to read and be patient today
Thank you for the link
I have sylvanias that are clear as well. My only ones that arent came from the pictured green/black boxes. Mine that arent clear are about 10yrs newer and have different boxes. These sylvania i was informed are from the 50s, at least by the guy who gave them to me. I haven't actually got down looking at date codes or anything
ive found several additional pairs on ebay that have dark glass and green/blk boxes ive purchased but not received yet as well. One matched pair is out for delivery atm. I def want as many of these particular sylvania tubes as i can get my hands on though, thats for sure.
I do know carbon has anti electrostatic properties. Iirc, thats the entire reason for is presence in a vinyl record. And i don't have to shield these tubes like my clear 6ag5. I lean towards the carbon rings having something to do with electrostatic interference.
All* of my clear 6ag5, when i put my hand close to them hiss and puff like nobody's business. These dark glass Sylvanias do no such thing. They dont do anything at all even if you touch em directly.
The old living room TV, if i put ANYthing tube near it, i can hear intense transformer noise through the circuit unless i shield the tubes. Its a samsung tv like 15 years old. I shouldn;t even be using it, the chassis is live with 24v and it can give you some tingles if ya touch the wrong area while grounded like an oldschool oven with a ground fault.... But it still works so i still use it lol.
Have to use shields even on the 12ax7 breadboards because of the nose that TV puts out and i take the circuits in there to hear them in a bigger room pretty frequently. And it's not even electrostatic, its electromagnetic interference. I dont have to shield the darkglass tubes in there. Idk what's going on there with these tubes, but im inclined to think probably has something to do with the darker carbon treated glass. But i have no idea. That's just been a bonus on top of them sounding better to my ears though. Maybe they are engineered this way to perform better near the intense electromagnetic interference of oldshool flyback transformers or something. Beats me. I do know with 100% certainty i saw dark tubes in oldschool floor standing TV's as a kid, but that doesn't mean they weren't just old electron bombarded glass.
ive found several additional pairs on ebay that have dark glass and green/blk boxes ive purchased but not received yet as well. One matched pair is out for delivery atm. I def want as many of these particular sylvania tubes as i can get my hands on though, thats for sure.
I do know carbon has anti electrostatic properties. Iirc, thats the entire reason for is presence in a vinyl record. And i don't have to shield these tubes like my clear 6ag5. I lean towards the carbon rings having something to do with electrostatic interference.
All* of my clear 6ag5, when i put my hand close to them hiss and puff like nobody's business. These dark glass Sylvanias do no such thing. They dont do anything at all even if you touch em directly.
The old living room TV, if i put ANYthing tube near it, i can hear intense transformer noise through the circuit unless i shield the tubes. Its a samsung tv like 15 years old. I shouldn;t even be using it, the chassis is live with 24v and it can give you some tingles if ya touch the wrong area while grounded like an oldschool oven with a ground fault.... But it still works so i still use it lol.
Have to use shields even on the 12ax7 breadboards because of the nose that TV puts out and i take the circuits in there to hear them in a bigger room pretty frequently. And it's not even electrostatic, its electromagnetic interference. I dont have to shield the darkglass tubes in there. Idk what's going on there with these tubes, but im inclined to think probably has something to do with the darker carbon treated glass. But i have no idea. That's just been a bonus on top of them sounding better to my ears though. Maybe they are engineered this way to perform better near the intense electromagnetic interference of oldshool flyback transformers or something. Beats me. I do know with 100% certainty i saw dark tubes in oldschool floor standing TV's as a kid, but that doesn't mean they weren't just old electron bombarded glass.
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My trip through the old storage trailer did not turn up any 6AG5's or 6186's. I know that I had several hundred at one time since I have a picture of the box full. They are in the middle bin in the fourth row from the top. Bet you never saw a 6AG5 with a spare heater included. How about two of them. I had over 100,000 tubes all pulled from "military spares" that were being stripped for parts and sold for the metal scrap value. I had to move what I wanted to keep about 1200 miles, so I sold, gave away or trashed a lot of tubes that I did not have a need for. I thought the 6AG5/6186 made the trip, but I can't find them.
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it wouldnt surprise me they didnt make it. No one uses 6ag5 these days for anything unless they have a radio or tv restore that calls for them. The guy i got my box from when i bought an oscilloscope just gave them to me. Said ebay didnt want them and he only has 1 radio that uses them and he doesnt use that radio.
Cant find a single audio circuit that wasn't a guitar pedal or preamp that use them. Initially i started at op points for a 6au6 design and worked from there for them. Using them as triodes.
Definitely sounds like a box of tubes someone would easily let go of and not pay too much mind. 6AG5, at least in my limited experience, does seem to be one of those under appreciated gems you sometimes find in the tube world though. Especially these little dark glass sylvanias. Put a nice little grounded shield on em though, and all the 6ag5 i have are absolutely phenomenal sounding. I keep tinkering with other tubes and breadboards, but just find myself listening in the evenings through the 6ag5's by preference every time so far
Cant find a single audio circuit that wasn't a guitar pedal or preamp that use them. Initially i started at op points for a 6au6 design and worked from there for them. Using them as triodes.
Definitely sounds like a box of tubes someone would easily let go of and not pay too much mind. 6AG5, at least in my limited experience, does seem to be one of those under appreciated gems you sometimes find in the tube world though. Especially these little dark glass sylvanias. Put a nice little grounded shield on em though, and all the 6ag5 i have are absolutely phenomenal sounding. I keep tinkering with other tubes and breadboards, but just find myself listening in the evenings through the 6ag5's by preference every time so far
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The old brain gets a bit foggy with details..... I was given over 100,000 loose used, unsorted, and untested tubes that were found in an abandoned warehouse that was scheduled to meet the bulldozer when someone found traces of mercury and yelled HAZMAT. Vagrants, homeless people, and druggies had trashed the place, breaking lots of tubes and all of the glass windows, so everything that remained was covered in pigeon poop.
After discarding the trash and giving all the non useful (10KV rectifiers, thyratrons, etc) stuff to a tube dealer, I sorted the remains in racks like those in post #13. If the tube type was something I had not previously seen, I tried to test a few of each type in a working audio circuit. Most of the 7 pin pentodes, heptodes, and hexodes have a compatible pinout, so I ran them all through the same audio amp listening to the sound quality from one channel while measuring gain and THD in the other. No attempt to tweak the circuit for optimal results for each tube was made. The amp used to test all the 7 pin tubes, and 12 pin Compactron output tubes was a hacked up version of Pete Millett's Engineers Amp board (top board in picture). My flavor pushed his 18 WPC board to 250 WPC, with a commonly built version making 125 WPC. In this application the original 6CB6 tube did not quite have enough gain to reach 125 WPC from a CD player output, so I switched to the 6GU5 tube, as did Pete.
I found a 40 gallon tote full of bagged compatible 7 pin tubes in my storage building. The 6AG5's were not among them. Either they got stashed somewhere else, sold, or given away. I know that I took bags and boxes of tubes to all of the South Florida hamfests for a few years once I knew that my 40+ year engineering career was on life support and sold, traded, or even gave away stuff I didn't want pay to move. It is entirely possible that a different test circuit, or different parts values in the same amp could have resulted in a different outcome. Your particular circuit, amp components, system, and even music choices may favor the 6AG5 over other similar tubes. I'm pretty sure the 6GU5 will not be the optimum choice this time since I have over 20 different 7 pin tubes (including 3 NOS 6AG5's) and about a dozen 9 pin tubes to try.
10+ years have passed since that testing and I'm finally getting back to the little 7 pin tubes. This time the application is a guitar amp, and the 7 pin pentodes will also be competing with some 9 pin pentodes. This time the test circuit will be far more flexible in component choices, and extra weight is given to tubes that I have a bunch of, and that are readily available at several suppliers.
After discarding the trash and giving all the non useful (10KV rectifiers, thyratrons, etc) stuff to a tube dealer, I sorted the remains in racks like those in post #13. If the tube type was something I had not previously seen, I tried to test a few of each type in a working audio circuit. Most of the 7 pin pentodes, heptodes, and hexodes have a compatible pinout, so I ran them all through the same audio amp listening to the sound quality from one channel while measuring gain and THD in the other. No attempt to tweak the circuit for optimal results for each tube was made. The amp used to test all the 7 pin tubes, and 12 pin Compactron output tubes was a hacked up version of Pete Millett's Engineers Amp board (top board in picture). My flavor pushed his 18 WPC board to 250 WPC, with a commonly built version making 125 WPC. In this application the original 6CB6 tube did not quite have enough gain to reach 125 WPC from a CD player output, so I switched to the 6GU5 tube, as did Pete.
I found a 40 gallon tote full of bagged compatible 7 pin tubes in my storage building. The 6AG5's were not among them. Either they got stashed somewhere else, sold, or given away. I know that I took bags and boxes of tubes to all of the South Florida hamfests for a few years once I knew that my 40+ year engineering career was on life support and sold, traded, or even gave away stuff I didn't want pay to move. It is entirely possible that a different test circuit, or different parts values in the same amp could have resulted in a different outcome. Your particular circuit, amp components, system, and even music choices may favor the 6AG5 over other similar tubes. I'm pretty sure the 6GU5 will not be the optimum choice this time since I have over 20 different 7 pin tubes (including 3 NOS 6AG5's) and about a dozen 9 pin tubes to try.
10+ years have passed since that testing and I'm finally getting back to the little 7 pin tubes. This time the application is a guitar amp, and the 7 pin pentodes will also be competing with some 9 pin pentodes. This time the test circuit will be far more flexible in component choices, and extra weight is given to tubes that I have a bunch of, and that are readily available at several suppliers.
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I may have omitted that Im actually using the 6AG5 in triode arrangement for the audio preamp, seem to get a little more gain, a little less THD, and a soundstage character i much (overwhelmingly so) prefer to using them as pentodes. Does not surprise me one bit the 6ag5 data sheets all have listed spec for use as triodes in class A audio amplifiers as an intended use-case scenario. Someone back then during product development was prob like "Man, these sound really good as audio triodes".
Using them in a pentode arrangement i actuall prefer the 6au6, but i prefer both of them, at least in a stereo linestage preamp, when used as triodes not pentodes.
I am tinkering with some guitar preamp and clean boost circuits using these little pentodes too. I think, for guitar, i prefer them in a pentode arrangement and the way they break up, but i also haveny spent a lot of time there yet. Im also just running into the input on a focusrite interface, not an actual guitar amp rn, but the front end of the low level instrument input is designed to respond like the front end of a clean amp when you dial it in to your signal intensity, impedance/impedance wise, and i even have a little button to engage light analog breakup in the signal lol. The 6ag5 i do prefer here to 6au6 as well, when i push their front end, i prefer their breakup over the 6au6 for sure, and when totally clean, the sound is bigger it feels like. The 6ag5 do have more noise then 6au6 here though. Noise that shields dont seem to help.
(i've actually been unreasonably impressed with how the modern amp sims respond to being hit with a clean boost etc. In-daw modeling is getting nuts, so are the interfaces, i can even run a ts-9 into this interface and my sims respond as you would want to expect them to)
Obviously i have very limited experience with implementing tube variety though, im workin on that slowly but surely..
Using them in a pentode arrangement i actuall prefer the 6au6, but i prefer both of them, at least in a stereo linestage preamp, when used as triodes not pentodes.
I am tinkering with some guitar preamp and clean boost circuits using these little pentodes too. I think, for guitar, i prefer them in a pentode arrangement and the way they break up, but i also haveny spent a lot of time there yet. Im also just running into the input on a focusrite interface, not an actual guitar amp rn, but the front end of the low level instrument input is designed to respond like the front end of a clean amp when you dial it in to your signal intensity, impedance/impedance wise, and i even have a little button to engage light analog breakup in the signal lol. The 6ag5 i do prefer here to 6au6 as well, when i push their front end, i prefer their breakup over the 6au6 for sure, and when totally clean, the sound is bigger it feels like. The 6ag5 do have more noise then 6au6 here though. Noise that shields dont seem to help.
(i've actually been unreasonably impressed with how the modern amp sims respond to being hit with a clean boost etc. In-daw modeling is getting nuts, so are the interfaces, i can even run a ts-9 into this interface and my sims respond as you would want to expect them to)
Obviously i have very limited experience with implementing tube variety though, im workin on that slowly but surely..
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Its my own design, attached is a hand drawn schematic as it sits right now. running as triode with around 100v across the plates at something around 10ma real world i believe. I'd have to measure and re-math to say for sure, been a couple weeks since ive tinkered with it and i dont remember now. I think it's like -1 at cathode i think. Im planning on redoing the breadboard to play with a higher voltage transformer whenever i get around to it. I have the transformer, but im also already more then satisfied with the performance. Im series heating the tubes from 12.6v because i didnt have the appropriate power resistors to pad it down to 6.3v yet. Do now though, but havent tinkered there in a bit either. The yard and gardens been taking my free time up recently so my 6ag5 breadboard has sat as is for a bit now
The difference between the dark glass 6AG5 and the clear glass is honestly kinda striking. My dark glass 6ag5 are hands down the best soundstage i have access to in all my tubes. The difference is striking enough that it actually confuses me pretty good. I have some yellow box sylvania 6ag5 matched pairs on the way from ebay now too. They also had the dark glass, im curious if they'll be as sound-stagey as the green/blk boxes. every time i switch the tubes out, im like "Ok, not too different" and ill listen for a while, but when i pop the dark glass in my jaw flies open every time 🤷♂️ Every time i say darkglass, it's reminding me of those bass guitar preamps that use the name DarkGlass, and how much better they sound then anything else available in the bass guitar preamp world. There's definitely something interesting to the dark glass sylvania 6ag5.
As far as i can tell looking at date codes and pictures online, all of my clear glass 6ag5 are quite a bit newer then my dark glass. But i also don;t know for sure if im even reading the date codes correctly, i know sometimes they arent what they seem.
This design started from a 6au6 triode design i found somewhere deep in the old bowels of diyaudio through the search function lol
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