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Arcing rectifier -- seeking sage advice

Good instincts - that cant possibly be how a good tube is supposed to behave. Was it shipped in place - in socket? Package may have taken a good, solid landing somewhere long the way, which could have moved some structure inside it slightly.
All the tubes were contained in a padded box within the main box (not in the sockets). Inside the 'tubes' box, each individual tube was within it's own custom shaped box... Extremely well packed, and yet still damaged 🙄
 
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Extremely well packed,
Hopefully the guy you bought it from gets to see the video too. Even if he just confirms "something changed" between when he sent it off and what it's doing now.
ss diode in series with each tube diode anode
One would think they'd make a socket adapter that does that - still get the tube rectifier sound - but with SS reverse protection.
 
Hopefully the guy you bought it from gets to see the video too. Even if he just confirms "something changed" between when he sent it off and what it's doing now.
I shared the video with him via email, and he agreed that the tube is dead. He commented that tubes are like an incandescent bulb with shaky filaments, and just the act of shipping it killed it. This is a relief, as it means he didn't use it while with the tube in this state. He's pretty knowledgeable, and a caring owner, so I'm not surprised.

So... I guess this tale is pretty much wrapped up. Luckily new tubes are fairly cheap and plentiful. My final concern with this is whether any auxiliary damage may have occurred during the two times I fired the amp up with this dead tube, even though it was only for 3 seconds the first time + 30 seconds the last time. Anyone have input about the chances of this? The fuse didn't blow, which I suppose is a good sign... but on the other hand maybe it would have been better if it did blow... Idk.

One would think they'd make a socket adapter that does that - still get the tube rectifier sound - but with SS reverse protection.

That sounds like a great idea, because then it's not a 'hard mod', and could be easily added or removed depending on user preference... It would be especially good for classic, well regarded designs where any modification would degrade it's value and be considered a 'negative' by many... Like this Yamamoto.
 

6A3sUMMER

Member
2016-06-07 6:50 am
As long as the tube shorting/arcing did not destroy the B+ electrolytic capacitors, all you need is a new rectifier.

But if one of the electrolytic capacitors was previously/already shorted (aged/dried out, over-voltage, etc.), then the electrolytic destroyed the capacitor.

If the amplifier was previously run without the output tubes in place (or dead output tubes), the un-loaded B+ on the caps goes to 1.4 x VACrms (very low voltage drop in a vacuum tube rectifier that has very low current load). [some designers forget to use electrolytics that are rated for 1.4 x VACrms].

Chicken then the egg? Bad tube, then bad electrolytic?
Egg then the chicken? Bad electrolytic, then bad tube?

Fusing an amplifier's power transformer primary . . .
Example of what I use for one of my low power amplifiers:
1.5 Amp Fast Blow ('lives through' the turn-on transient current of solid state rectifiers charging B+ electrolytics that are at 0 Volts, and cold filaments; but then 'opens up' if there is a short in the B+),
Ant then a 0.6 Amp (600mA) Slow Blow, in series with the Fast Blow.
The Slow Blow easily takes the 1.25Amp turn-on transient current, but 'opens up' if the steady state primary current of 500mA goes to 700mA from an output tube going into thermal run-away, or an electrolytic cap that is getting very leaky, etc.

For amplifiers that I modify, or use just the chassis and power transformer, to create a completely different topology, etc. . . . I do not worry about the loss of value of a previously original classical amplifier.
To me the value is in the fun of modifying, and getting something that I like and . . . listen to.

Imagine if Jay Leno never had gas put in one of his cars and drove it.
They are not just museum cars, they get driven and appreciated (Wow! doesn't the value go down each time he drives a classic car?).
 
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As long as the tube shorting/arcing did not destroy the B+ electrolytic capacitors, all you need is a new rectifier.
For the tube aficionados -- In the video I posted, is there any arcing or shorting apparent here, visually or auditorily? I wonder if we're just looking at a really gassy tube firing up... my reasoning being that the fuse never blew, and the other tubes seemed to be glowing 'normally' (if perhaps slightly dim). Also, there were no loud sounds from the tube (popping, buzzing, crackling, etc.), which I would imagine would accompany an arc. I am, of course, going to replace it either way...

Good points raised in your post 6A3sUMMER... You'd probably be able to rebuild the amp from scratch, with improvements along the way. Me, I'm still in 3rd grade :-0

If the -potted- first filter (near the choke) capacitor (oil filled PP in ebony case?) destroyed, it's a problem. I think it's special one (Obligato?).
Ya, that would be disappointing to say the least, especially because of those custom caps... I would hope the fuse would go first -- it should, right?
 
80 tubes are not that robust. I had an 80 arc at startup in my A08. I checked the amp in the bench: everything was fine. I installed a new 80 and all was well. Notice that the amp has an ammeter. The ammeter should provide confidence that all is well with a new rectifier tube. Each 45 should draw about 32mA. It the two output tubes are drawing normal current then all is well.
 
Is the tube in the video really a 80? Or has someone swapped it for a 83 previously?
Ha, I had the same thought. Maybe this is how 83s are made -- they are born of gassy 80s, like a butterfly emerging from a cocoon :).

To answer seriously, the tube is certainly an 80, verified by the original labeling.


I had an 80 arc at startup in my A08
Ah, a fellow Yammy owner. Do you remember if it blew a fuse? Did it look similar to what my video showed?

I'm glad to know yours didn't suffer any damage.
 
Interesting -- I'm shopping for a replacement as we speak.

I wonder if an arcing tube usually doesn't damage anything else except for rare occasions, and the 'damage' is all contained in the tube it's self... or, rather, if it's common for it to take out other components. I suppose much of it depends on the particular circuit that it is in...
 
When the water pump goes out on your car, and the motor is run for 5 minutes more . . .

The damage to the motor (or no damage) is according to the ambient temperature (below zero, above 100 degrees F); the specifics of the oil; and the make and model of the car (motor specifics).
 
I wonder if an arcing tube usually doesn't damage anything else
It would be interesting to put in the hypothetical SS diode reverse voltage protector socket adapter and see if the nature of the arc changes. That would tell you if the arc is only conducting in the direction the tube diode is supposed to conduct, or, if it's conduction is in both directions. It's that reverse conduction I suspect would do damage...

If the tube starts conduction in the forward direction, then arcs, then extinguishes in the reverse, how could that be worse than a SS diode with its Volt or so forward drop? Assuming the rest of the amp's powersupply circuit could "take" a full SS rectifier substitute...
 
If a dual diode tube starts arcing then it certainly stresses the power transformer secondary, as there is then a short circuit path between both diode anodes (one anode conducts to the cathode as per normal forward conduction, and the other anode arcs from cathode to anode as per a reverse breakdown). The voltage on the first filter cap can get ugly, depending on whether the arcing is just to one anode, in which case the first filter capacitor could plausibly be stressed by high ripple current (if it were an e-cap).

The ss protection diode in series with each valve diode anode has to have sufficient PIV rating for the application - that typically means 1x 1N4007, but could mean 2x or 3x in series for higher B+ levels. That part of the circuitry experiences quite high voltage, so best to add the ss diodes without cutting corners by using adjacent valve base terminals.
 
When the water pump goes out on your car, and the motor is run for 5 minutes more . . .

Now I'm wishing I didn't even turn it on again, let alone for another 30 seconds... but, oh well, I had to do it in order to figure out what was actually happening, I suppose... Plus, I had to make a cool movie for you guys to see :cool:.

Thanks all for the input -- very helpful, and good to piece together an understanding based on different outlooks and ideas.

Oh well, tons of discussion on an issue that could be solved quickly and simply by replacing the bad tube :rolleyes:...

True -- however, at this point for me, it has become more of an academic curiosity... I'm building my understanding of tubes in general, from a fairly novice perspective. Practically speaking, I'm good at this point -- the beginning parts of this thread helped me realize I just need a new tube.

On that note, I now dig deeper (crowd gasps), for anyone who may want to venture into the land of theory and physics with me...

It appears as though the only time the tube arcs is within the first few seconds, and then it seemingly stabilizes. It almost seems like I could have kept it running for some time with no issues, after the initial 'rough start'... Why would this be?

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... Any theories?