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Is this arcing?

tea_hous

tea_hous

Member
Hey everyone... been a long time since I've posted to AK :0. I'm here seeking some input from those who have more knowledge and experience with tubes than myself.

I just purchased a Yamamoto A-08s, and one of the tubes was damaged in shipping (despite being packed very well). Its an '80' rectifier, presumably from the 1930's or 40's. After carefully setting everything up, I powered it up for the first time, and immediately noticed something awry. I shut it off after a couple seconds. Then, a couple days later, I decided I needed to try it again to get a better assessment of what was happening, and employed by wife as a videographer for the event :). This time, I ran it for about 30 seconds before powering it back down.


So, It's obvious that the tube needs to be replaced -- I'm already searching, and luckily they aren't that expensive either. What I'm posting this for is twofold -- I'm fairly inexperienced with tubes, so I want to educate myself in knowing whether I was witnessing arcing or something else. I'm also concerned that if it actually was arcing, that there may be damage to something else in the circuit, such as those expensive transformers or the hand made capacitors :(.

The fuse did not blow, and there were no loud noises coming from the tube that I assume would accompany arcing (popping, crackling, etc.). It almost looks like the tube has become very gassy and / or broke a filament, which may be why the left plate is glowing so brightly (?). I'm not sure -- maybe the flashing we see at the very beginning has to do with the gas being 'excited', or somehow burning off, but not actually causing any electrical arcing? I do notice that the gas seems to 'thin out' immediately when the tube flashes a few times on initial power up...

Thanks everyone for any and all input!
 
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Yes that is arcing, that tube is toast.

Since you didn't run it long the caps should be fine. One thing is for sure, you'll know when you plug a new one in :thumbsup:

PS, the 5Y3 is electrically the same, but came in better variants like the 5Y3WGTA . A tube base adapter (5Y3 female to 80 male) would be a cheap way to use a somewhat more modern directly heated dual diode....


From Wiki;


"The 5Y3 is a medium-power directly heated full-wave rectifier vacuum tube introduced by RCA in 1935. It has found wide use in tube radios and early guitar amplifiers (of the Fender Champ type). It is virtually identical, electrically, to the older four-pin type 80 tube, but with an octal base. 5Y3G, 5Y3GT, and 5Y3WGTA are variants with essentially the same specification".
 
tea_hous said:
Hey everyone... been a long time since I've posted to AK :0. I'm here seeking some input from those who have more knowledge and experience with tubes than myself.

I just purchased a Yamamoto A-08s, and one of the tubes was damaged in shipping (despite being packed very well). Its an '80' rectifier, presumably from the 1930's or 40's. After carefully setting everything up, I powered it up for the first time, and immediately noticed something awry. I shut it off after a couple seconds. Then, a couple days later, I decided I needed to try it again to get a better assessment of what was happening, and employed by wife as a videographer for the event :). This time, I ran it for about 30 seconds before powering it back down.


So, It's obvious that the tube needs to be replaced -- I'm already searching, and luckily they aren't that expensive either. What I'm posting this for is twofold -- I'm fairly inexperienced with tubes, so I want to educate myself in knowing whether I was witnessing arcing or something else. I'm also concerned that if it actually was arcing, that there may be damage to something else in the circuit, such as those expensive transformers or the hand made capacitors :(.

The fuse did not blow, and there were no loud noises coming from the tube that I assume would accompany arcing (popping, crackling, etc.). It almost looks like the tube has become very gassy and / or broke a filament, which may be why the left plate is glowing so brightly (?). I'm not sure -- maybe the flashing we see at the very beginning has to do with the gas being 'excited', or somehow burning off, but not actually causing any electrical arcing? I do notice that the gas seems to 'thin out' immediately when the tube flashes a few times on initial power up...

Thanks everyone for any and all input!
Click to expand...
Good source for tubes. https://www.tubemonger.com/GE_CANADA_5Y3GT_NOS_NIB_1960s_Black_Plate_Zaerix_p/1059.htm
 
I blew one up about a week ago, Chinese 5AR4. First time I've ever had a tube rectifier actually go bad on me. I've had weak ones, but never one that put on a show.


might be worth confirming the fuse is correct too. If it didn't fail fairly quickly I'd wonder about that. The tube short I had flashed once and the fuse popped.
 
Good info all around! I gather from the lot of ya' that arcing rectifiers are more common than I had thought...I'm also gleaning that *usually* there will be no damage and the tube just needs to be replaced... so that's good news.

Now I'm curious from an academic point of view... Does it appear as though the only time it arcs is within the first few seconds, and then stabilizes? I wonder why this would occur, and if after those first few seconds there was nothing 'anomalous' being sent to the rest of the amp... So in theory I could have kept it running for some time with no issues, after than initial 'rough start'...

Furthering on this, I wonder what is occurring during those first few seconds. It looks at first like the gas is light blue, and most brightly illuminated and dense on the bottom of the tube. This lasts for a second or two. Then something sparks and flashes a few times, and the gas content instantly changes to being a more purplish color and glowing more diffusely, with a bright spot on top of the tube...
 
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In theory no you cannot leave it running or it will self destruct and possibly cause fire

Don't use it. It is a bad tube which looks to me to have a cracked or broken bulb. Depending on which pin the high voltage is taken off of 2 or 8 is why it looks like only one side is arcing. The other side could be completely destroyed.

Getting a new 80 tube (or 5Y3 with adapter) that is good will glow normally just like the other tubes. The two halves heating filiments are directly heated and it only takes a few seconds for the tube to start conducting B+ current.
 
if it arcs initially and stops, I'd guess its a case of elements being too close together and it arcs when the voltage at the cathode is zero, prior to charging the supply caps. Once they charge up, the voltage difference isn't enough to make it arc.

Not sure how the filaments are supported on the 80, but some of the early tubes had what looked like a coat hook up top that the filament looped over. If that support has bent or whatever the filament gets too close to the plate.

Typically gas will stay glowing the whole time the tube is flowing current, though it does usually show up as a pink or purple glow inside the plate structure.

and no I wouldn't continue to run this. If the tube shorts it can take out the power transformer and thats a whole lot more expensive than a tube.
 
tea_hous said:
Good info all around! I gather from the lot of ya' that arcing rectifiers are more common than I had thought...I'm also gleaning that *usually* there will be no damage and the tube just needs to be replaced... so that's good news.

Now I'm curious from an academic point of view... Does it appear as though the only time it arcs is within the first few seconds, and then stabilizes? I wonder why this would occur, and if after those first few seconds there was nothing 'anomalous' being sent to the rest of the amp... So in theory I could have kept it running for some time with no issues, after than initial 'rough start'...

Furthering on this, I wonder what is occurring during those first few seconds. It looks at first like the gas is light blue, and most brightly illuminated and dense on the bottom of the tube. This lasts for a second or two. Then something sparks and flashes a few times, and the gas content instantly changes to being a more purplish color and glowing more diffusely, with a bright spot on top of the tube...
Click to expand...

What's going on is that with a directly-heated rectifier like the 80, the tube is getting socked with full voltage at turn-on, before the other tubes have a chance to start conducting, with no slow warm-up. Depending on the condition of the tube, it just can't handle the instant voltage and current surge. This can also happen when the first cap in the power supply is too large.
 
One other quick thing of mention, in my first response to this thread I proclaimed the tube toast because the type 80 is not supposed to emit light like that.

But !

The type 80 has a distant cousin that looks pretty darned similar, the type 83. I mention the 83 because it's a mercury tube, plugs right into the 80 socket and IS supposed to have a bright blueish / purple glow. Since the OP said he saw sparking, I'm betting it's an 80 and it's toast. I just figured I'd mention for future reference a blue glow isn't always the harbinger of doom depending on what tube it is, as in the case of the type 83.......

tube 83.jpg
 
Woah, three excellent explanations -- lucky me. Thank you, I feel like I 'get it' on a deeper level now.

I just purchased a National Union NX-280 globe as a replacement... reportedly tested very strong, and looks good... hopefully this one makes the journey intact and works well.

init4fun said:
The type 80 has a distant cousin that looks pretty darned similar, the type 83.
Click to expand...

Ha, what if, throughout this entire thread, we were just observing a healthy '83' tube in action :p. I had the same thought when I first started to research this, and a couple other people brought the possibility up as well (through PM). I double checked the engraved labeling and verified it was an 80, even before I posted here. Good thinking though, and it's bizarre how 'alike' my gassy 80 looks to a healthy 83!

Would an 83 work as a direct replacement for an 80? I don't actually want to do this, but just curious.

gadget73 said:
and no I wouldn't continue to run this. If the tube shorts it can take out the power transformer and thats a whole lot more expensive than a tube.
Click to expand...

My writing may have sounded ambiguous whether I actually wanted to try to keep running my broken tube -- no way, I'm way too careful and worried to do that, especially with my new Yamamoto. I'm just in the land of 'theory'.

If a tube does short, that's such a catastrophic consequence, to take out a power transformer... yikes, all from a wire moving a few millimeters. I wonder, should the fuse blow immediately in this case, hopefully saving the transformer from any damage?
 
init4fun said:
Yes that is arcing, that tube is toast.

Since you didn't run it long the caps should be fine. One thing is for sure, you'll know when you plug a new one in :thumbsup:

PS, the 5Y3 is electrically the same, but came in better variants like the 5Y3WGTA . A tube base adapter (5Y3 female to 80 male) would be a cheap way to use a somewhat more modern directly heated dual diode....


From Wiki;


"The 5Y3 is a medium-power directly heated full-wave rectifier vacuum tube introduced by RCA in 1935. It has found wide use in tube radios and early guitar amplifiers (of the Fender Champ type). It is virtually identical, electrically, to the older four-pin type 80 tube, but with an octal base. 5Y3G, 5Y3GT, and 5Y3WGTA are variants with essentially the same specification".
Click to expand...
RCA repurposed a number of older tube types on their then-newly introduced octal bases, this is one of several.
 
tea_hous said:
should the fuse blow immediately in this case, hopefully saving the transformer from any damage?
Click to expand...

well, I'd hope so, but if the fuse is incorrect or just too big, it may not.

The amp I brought up the other day with the bad rectifier popped the fuse immediately, I didn't even realize what had happened other than when I went to measure something after giving it a few minutes to warm up, it had zero volts everywhere and the tubes were dark. When I replaced the fuse and brought it up on the bench, I got to about 70 volts on the variac, got a lightning show and the ammeter banged off the end of the 3 amp scale. Didn't take out the fuse that time because I cut the power. Its a home-brew amp from the late 50s and came to me with a 2 amp fuse installed. It seemed like a reasonable value so I left it be.
 
gadget73 said:
well, I'd hope so, but if the fuse is incorrect or just too big, it may not.
Click to expand...

Ah, ok good -- for a moment, I was questioning if I misunderstood the efficacy of the fuse. Ya, I'm going to set a mental reminder to check the fuse on all my new (used) gear... never know what the previous owner did.

Say the fuse doesn't blow -- how long does it take to destroy the transformer? Seconds, minutes? Also, what actually happens to destroy it? I'm assuming overheating and melting of alloys (with a low melting point), leading to fusing / bridging where there should be an air gap?
 
tea_hous said:
Would an 83 work as a direct replacement for an 80? I don't actually want to do this, but just curious
Click to expand...

Generally, no.

Type 80 has a 2 amp filament whereas type 83 is a 3 amp filament. The filtering circuit for the 83 is of a more complex design due to it being a mercury vapor tube VS a regular high vacuum tube like the 80. Type 83's principal benefit is that regardless of load the voltage drop across it remains constant, this coming at the expense of the additional filtering required to eliminate the additional noise of the mercury vapor.
 
tea_hous said:
Ah, ok good -- for a moment, I was questioning if I misunderstood the efficacy of the fuse. Ya, I'm going to set a mental reminder to check the fuse on all my new (used) gear... never know what the previous owner did.

Say the fuse doesn't blow -- how long does it take to destroy the transformer? Seconds, minutes? Also, what actually happens to destroy it? I'm assuming overheating and melting of alloys (with a low melting point), leading to fusing / bridging where there should be an air gap?
Click to expand...

The transformer is made of several pieces of various gauge enamel covered wire wrapped around an iron core. When it's overloaded it gets hot, too hot, and the enamel that's supposed to be insulating the windings from each other melts and allows the windings to begin to electrically conduct to other windings. This shorting of the windings causes it to draw even more current than the overload is presenting and the poor transformer is done for. Burnt transformers have a specific smell that once you've smelled it you'll remember it for life.

As to the time to achieve meltdown? That is completely dependent on the degree to which it's overloaded.......
 
Ah, good info on both posts -- you guys are tube university professors.

So... pretend scenario -- let's say I install a new (old) rectifier, and I don't notice that there is a short by visual inspection... I install it and fire the amp up, and by unfortunate circumstance, the fuse is faulty and fails to blow. How would this 'movie' play out? Would it be immediately obvious through other signs and events that something is seriously wrong, or would it rather be sort of a 'silent killer' where a few minutes later I start to smell smoke, as the transformer wires melt and other things overheat and burn?
 
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