Today one of the tubes in my amp failed, didn't see it coming, no flashes, no smoke, buzz, hiss, just died quietly. Upon inspecting it closely I see the cloudiness on the glass envelope that looks like the result of getters spewing beams of electrons. There are also cracks in the glass base, where the connecting wires go from the glass envelope to the pins. Could it be that cracks in the glass compromised the vacuum in the tube causing it to fail? The mesh plate looks spotless - no browning, discoloration or deformations. I don't have a tester that could test 300B.
When in the circuit the filaments were not glowing, there are no shorts between filaments and anode/cathode, and filament itself seems to be conducting (according to my DMM). Replacement tube seems to be working fine, heater voltage measured 5VDC exact.
What would cause a tube failure like this? Could it be manufacturing defect? The tube in question is not exactly cheap and has good reputation.
When in the circuit the filaments were not glowing, there are no shorts between filaments and anode/cathode, and filament itself seems to be conducting (according to my DMM). Replacement tube seems to be working fine, heater voltage measured 5VDC exact.
What would cause a tube failure like this? Could it be manufacturing defect? The tube in question is not exactly cheap and has good reputation.
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Looking at ur nice well focused pix, I can't clearly see a stress crack through the base envelope, to the outside air. If it is there, even a micro path, that would kill the tube asap.
Looks like there has been stress cracking in two places?
I'd say this is a defect, but if the tube has many hours on it, I doubt the mfr will make good, no harm in asking, and sending along the pix.
If the tube shows no resting current and the filament lights properly, then it is definitely not conducting.
Since the replacement tube does work, it's a pretty safe assumption that it has failed, and likely that those cracks are the cause.
Do your other equal or similar hour tubes show any sign of cracking?
Looks like there has been stress cracking in two places?
I'd say this is a defect, but if the tube has many hours on it, I doubt the mfr will make good, no harm in asking, and sending along the pix.
If the tube shows no resting current and the filament lights properly, then it is definitely not conducting.
Since the replacement tube does work, it's a pretty safe assumption that it has failed, and likely that those cracks are the cause.
Do your other equal or similar hour tubes show any sign of cracking?
The other tube from the pair shows no cracking, this pair had approx 80 hrs on it. I also checked another pair of tubes (EH) that was used for a couple of years with this amp - no signs of damage.
I will send the tube to Mr. Wugang for them to review it. Knowing their reputation (Sophia) I would expect them to come up with something. Tube manufacture date is 12/16/2011.
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I called Sophia and was surprised to get Richard Dwu himself on the phone. I explained the matter to him and he asked me to send the pair back for them to look at. I would not expect them to replace the failed tube for free, maybe a discount on a matching tube to make a pair...
In regard to the cracks - in picture nr. 2 the crack is clearly visible. It is formed along the wire that runs from the base of the tube to the inside of the glass envelope and is baked into the inside of the glass pillar. There is a second, smaller crack that doesn't seem to run all the way.
In regard to the cracks - in picture nr. 2 the crack is clearly visible. It is formed along the wire that runs from the base of the tube to the inside of the glass envelope and is baked into the inside of the glass pillar. There is a second, smaller crack that doesn't seem to run all the way.
It is clear that the vacuum got compromised from the crack. The glass was not tempered properly on this one. I have the same tubes and they are reliable so far.
I agree. If this tube used the thick glass as 6C33 and GM70 this fail not happen.
Military tubes has many advantages...
Sophia 300b uses thick glass, much thicker than EH or ShuGuang. These tubes were "sitting" in my amp for quite a while before one of them quietly died. I am inclined to think that cracks developed from heating/cooling process of normal tube operation. shipping stress would manifest right after the shipping.
My worst "Oops" experience was receiving a confirmation from *** that a new 300B PP stereo power amplifier I shipped to a client was not delivered because the crate exited the vehicle three miles from the customer destination. Subsequently I found out that the driver apparently forgot to close the rear door on the delivery truck and my crated amplifier and a number of other packages tumbled out onto the roadway at speed. The crate bounced, tumbled, broke open and the amplifier fell out.. (Driver saw this in his rear view mirror, wonder if he still had a job afterwards.)
*** quickly admittedly their 100% culpability in the mishap, but their insurer dragged their feet for > 45 days before finally paying me.. They tried to weasel me down on the insured value as well which was just enough to cover. It took the threat of legal action against the insurer to get paid, and they then mailed the check overnight at a cost of > $100 when they could have mailed it a few days earlier for just a couple of $$.. 😱
I've generally had much better luck with the USPS in terms of getting things delivered in good condition than I have with either of their competitors. YMMV.. of course.. 😀
*** quickly admittedly their 100% culpability in the mishap, but their insurer dragged their feet for > 45 days before finally paying me.. They tried to weasel me down on the insured value as well which was just enough to cover. It took the threat of legal action against the insurer to get paid, and they then mailed the check overnight at a cost of > $100 when they could have mailed it a few days earlier for just a couple of $$.. 😱
I've generally had much better luck with the USPS in terms of getting things delivered in good condition than I have with either of their competitors. YMMV.. of course.. 😀
At YouTube there was a impressive video with mis-care on delivery from UPS, Fedex and others express companies, but seems it was removed by YOUTUBE staff:
http://www.youtube.com/watch?v=n1ZFCvSaGqI
It is amazing how big companies are protecting each others...
I received a response from Sophia claiming that the failure is due to shipping stress and that manufacturing defect would show up in 1-2 months...
I have to stress that these tubes were used in my amp for months and failure occurred one morning, during normal operation. The tubes were not handled in any way in the past 2-3 months. I suggested that the crack along the wire in the glass may have developed due to improper glass tempering and temperature swings during normal operation.
Sophia suggested I buy a matching replacement tube for $200, which is a full price. I bought a pair of these on A'gon for $285.00.
I have many other tubes, 300b as well, that were shipped more than once, cost less than half, and they continue functioning for years without failure. Needless to say I am a bit disappointed by Sophia Electric.
I have to stress that these tubes were used in my amp for months and failure occurred one morning, during normal operation. The tubes were not handled in any way in the past 2-3 months. I suggested that the crack along the wire in the glass may have developed due to improper glass tempering and temperature swings during normal operation.
Sophia suggested I buy a matching replacement tube for $200, which is a full price. I bought a pair of these on A'gon for $285.00.
I have many other tubes, 300b as well, that were shipped more than once, cost less than half, and they continue functioning for years without failure. Needless to say I am a bit disappointed by Sophia Electric.
I know, makes you wonder if the "premium" brand is worth the premium. At least when EH fails (never happened to me) you can replace it without cringing too much.
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I already expected this verdict. I would be surprised if they did not put the guilt on shipping.
This brand really dont stand by its products, I will take note it in my black list.
Worth to mention this brand big Triodes 211,845,805 are small plate dissipation, just 75W in Class A, even the 805 which are supposed to be 125W plate dissipation as the old NOS tubes.
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