[Gradofan2]

Quote:

Originally Posted by breakfastchef /img/forum/go_quote.gif Perhaps there is no problem at all. Although, the sparking Princess is a cause for concern. My assumption is that Woo Audio built every WA6 SE to specification. That does not mean that a component failed, which should fail soon after put into operation. That said, I do not think it is necessary to start talking about changing internal components. This is a potential Woo Audio warranty situation and you need to follow their intructions to flush out the anomaly.

If no one else has had a similar problem - I would think anyone would agree. In that event, it must either be a component failure (tube, or another) - or, an inconsistency in the specific amp from all the others (which is unlikely).

Whatever the circumstances... if no one else is experiencing the problem... it seems it would be a warranty issue. Though, it is unfortunate... that... it may require "the long and costly return" of the amp - to resolve the issue.

 

[Ragonix]

Quote:

Originally Posted by sclamb /img/forum/go_quote.gif Was that a 5AR4 or 5U4G?

It's a 5U4G.

 

[breakfastchef]

Gradofan2, I agree that a return to NY from the UK is a hardship. I wish this was not a problem that requires the return of a very wonderful amplifier. I would hope that Woo Audio would take the shipping cost into consideration if they, in fact, sent out a defective amp.

 

[sclamb]

Thanks for the last few messages. Rather than respond to each individually, let me just add that I will now wait for Jack's thoughts on the matter. I will of course share with you what needs to happen next.

 

[sclamb]

I got a response from Jack. Without directly quoting him, he said the response that I got from Sophia about the flash/spark maybe being caused by the amp cannot apply to his amplifiers. He did find white sparkle in one tube but not in another when used in the same amp when he did a test. However, his amps do not exceed 90ma. He will check with Sophia to see if this is a problem.

I will let you know of any further information.

 

[jamato8]

No, the amp does not exceed 90mA, it is around 70 to 75, as I have measured it but it isn't that it doesn't exceed the 90mA's, it is the inrush of current on turn on. That inrush can tax and exceed the tubes ability to supply current and you get arcing and sparks. Again, it could be a weak tube or something else. Arcing fries a tube.

 

[sclamb]

I understand. I believe that Jack is going to talk to Sophia Electric so hopefully he will find out what needs to be done.

 

[Parafeed]

Quote:

Originally Posted by jamato8 /img/forum/go_quote.gif That inrush can tax and exceed the tubes ability to supply current and you get arcing and sparks.

Concur. I'm coming at this from a DIY perspective, (I don't own the Woo amp), but in my experience using an input cap larger than 4uF, or choke input filter with low DCR HT windings and low DCR choke followed by a medium sized (50uF) cap, is asking for trouble. Even if the 274 is not arcing when new it will after a few months. You are damaging (and reducing the lifetime) of the tube, even if it can't be seen at the moment. Only Jack can answer regarding the DCR of the HT winding, DCR of the chokes, cap sizes, additional series resistance, etc. etc. I don't know if his circuit is C-L-C, L-C, or the component values used, but I would be interested in knowing if someone finds this information out.

 

[atbglenn]

Could a thermistor be used to soften in inrush current ?

 

[sclamb]

Quote:

Originally Posted by Parafeed /img/forum/go_quote.gif Concur. I'm coming at this from a DIY perspective, (I don't own the Woo amp), but in my experience using an input cap larger than 4uF, or choke input filter with low DCR HT windings and low DCR choke followed by a medium sized (50uF) cap, is asking for trouble. Even if the 274 is not arcing when new it will after a few months. You are damaging (and reducing the lifetime) of the tube, even if it can't be seen at the moment. Only Jack can answer regarding the DCR of the HT winding, DCR of the chokes, cap sizes, additional series resistance, etc. etc. I don't know if his circuit is C-L-C, L-C, or the component values used, but I would be interested in knowing if someone finds this information out.

Unfortunately I don't know enough about this subject to ask Jack the right questions, and I probably wouldn't understand his answers anyway. It would be great if someone here who is kowledgeable could ask Jack for the information.

It would seem odd if Jack has recommended a tube for his amp design wherein the usage of such tube would cause undue stress and short tube life. Paying 150 USD for a tube only to have it toasted by the amp is pretty poor I think.

 

[atbglenn]

Is Jack going to take care of you? I feel he should at least give you a new tube at no charge.

 

[sclamb]

Quote:

Originally Posted by atbglenn /img/forum/go_quote.gif Is Jack going to take care of you? I feel he should at least give you a new tube at no charge.

I honestly don't know but from the feel I get from communicating with him I think he will do the right thing.

Of course, toasting 274Bs could get quite expensive for him, and there is really no point in giving me another tube unless he mods the amp to work with it as I will just be toasting another one.

Either that or I find another tube that will be OK with the amp and that will give me as near to the performance of the Princess as possible (if such a tube exists).

 

[jamato8]

Quote:

Originally Posted by Parafeed /img/forum/go_quote.gif Concur. I'm coming at this from a DIY perspective, (I don't own the Woo amp), but in my experience using an input cap larger than 4uF, or choke input filter with low DCR HT windings and low DCR choke followed by a medium sized (50uF) cap, is asking for trouble. Even if the 274 is not arcing when new it will after a few months. You are damaging (and reducing the lifetime) of the tube, even if it can't be seen at the moment. Only Jack can answer regarding the DCR of the HT winding, DCR of the chokes, cap sizes, additional series resistance, etc. etc. I don't know if his circuit is C-L-C, L-C, or the component values used, but I would be interested in knowing if someone finds this information out.

]

Yep, it helps when you DIY. You really learn so much more and it is fun, well most of the time. I have no problem with my 6 but then I have totally modified it so that the rectifier would not be stressed. I explained to the importer for EML my circuit and he was fine with it and the 274B EML. The Sophia works fine also. Neither want to warranty if the cap is of the wrong size or if the inductor is not of enough DCR.

 

[atbglenn]

Quote:

Originally Posted by jamato8 /img/forum/go_quote.gif ] Yep, it helps when you DIY. You really learn so much more and it is fun, well most of the time. I have no problem with my 6 but then I have totally modified it so that the rectifier would not be stressed. I explained to the importer for EML my circuit and he was fine with it and the 274B EML. The Sophia works fine also. Neither want to warranty if the cap is of the wrong size or if the inductor is not of enough DCR.

So you think we will be hearing more and more people having problems with this tube on unmodified Woo 6 and 6 SE's ?

 

[sclamb]

If every WA6 or WA6 SE is based on the same circuit, then either the amp is not compatible with the 274B tube, or some amps have faulty components that are not working properly. Given that there are two other people here that have reported flashes/sparking, and Jack said himself that he got it with one 274B tube he tried, I think the components are fine and that the amp needs a rework to function properly with this tube.

Alternatively, we find another tube to use, or accept that we may get 2,000 hours from a 274B rather than 5000 hours (or whatever the real numbers are).