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Old 13th April 2011, 05:54 PM   #21
evanc is offline evanc  United States
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alco,
I set up my se just as you ended up except for the mosfets. I used 2sk3565
data sheet http://www.toshiba.com/taec/componen...//77/10779.pdf
in light of this thread they seems less then ideal. I bought the parts before this thread developed. none the less my amp still sounds great. I wonder if it is worth removing the parts to change them.

Anyway have fun with your new toy...Evan
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Old 13th April 2011, 06:55 PM   #22
beeah is offline beeah  United States
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Thanks for the update, Alco - this is very helpful information. Congrats on your initiation into the SET club!

If the core does start to melt, however, please do let us know...
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Old 13th April 2011, 08:13 PM   #23
Alco is offline Alco  United States
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Evan,

Congratulations on your new amp !
It's too bad we're on opposite coasts, it would be interesting to hear our amps side by side.

Perhaps someone more knowledgeable can comment on what sorts of differences we should look for in the sound from using different MOSFETs. I think someone brought up phase distortion earlier in the thread.
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Old 13th April 2011, 08:27 PM   #24
Alco is offline Alco  United States
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@ beeah:

thanx,
and if I do have a melt down I'll email you some potassium iodide before I hit the core with seawater !
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Old 14th April 2011, 01:18 AM   #25
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Quote:
I wonder if it is worth removing the parts to change them.
I doubt it. THe Toshiba spec you referenced only goes to 100 volts. The reverse transfer capacitance is 10 pF at 100 volts, The Tubelab SE runs the mosfets well above 100 volts so the capacitance will be low.

I have had several theoretical discussions with the "solid state is evil" crowd about Phase Intermodulation Distortion. It is definitely possible for a device whose capacitance varies with the applied signal to cause a varying phase shift with applied signal creating PIM.

ANY solid state device can cause PIM. SO CAN MOST TUBES!

It is convienient that PIM can not be easilly measured. It is also convienient that none of the SS=evil crowd can tell me what PIM sounds like. I would think that PIM would cause a loss of high frequency detail. A capacitance that varies a few pF with the signal voltage will only affect the high frequencies.

Back when I was developing the Tubelab SE design I stuffed several different mosfets into the board. I tried some rather large ones just to see what happened. The largest fets seemed to cause a general HF rolloff, but I never heard anything that I could call PIM. My hearing was a lot better then than it is now too. The TSE does not suffer from lack of detail!
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Old 14th April 2011, 01:56 AM   #26
evanc is offline evanc  United States
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George,
Thanks for taking that little bit of doubt away. Now that the amp is running the only thing I want to do to it is turn it on and listen.
Evan
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Old 14th April 2011, 02:15 AM   #27
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If it works and you like it don't mess it up. Even if (more like when) you get the urge to tinker, wait until you have plenty of listening experience. After a while you will pick out some musical favorites to use for auditioning changes.

You want find music that "thrills you", stuff that sounds amazing and couldn't possibly sound better. You also want to find stuff that could sound better. Then audition that music on several other systems to see if it indeed can be better, or the good stuff can be messed up. I don't know how much time I have spent trying to clean up bad sound that is in the source material.

Some music sounds best on a SE amp and the TSE is one of the best, some music sounds best on a P-P amp. I have not found one amp that fits all music.
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Old 3rd November 2011, 12:55 AM   #28
Alco is offline Alco  United States
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Default Bad News !

Well, I got seven harmonious months with my new TSE.....and then it blew up. Or at least it's blowing fuses. And I suspect my MOSFETS.

I haven't done much troubleshooting yet, but the amp powers up, warms up the filaments, and then just when the B+ starts to come on line the fuse blows, and on one occasion I saw a tiny bit of lightning inside the rectifier. I've been using 2 amp fuses. The rectifier test ok but makes me skeptical of any future use.

I've pulled the tubes and checked the PT; it seems fine.

How does one diagnose a blown MOSFET ?

And I'm back to deciding on which mosfet will work best. Perhaps I'll try the fairchild next......
Or maybe I'll just repurpose the transformers and build a simple SE. No mosfets to worry about there.

Anyways, I wanted to let people know before anyone else tries the vishays.
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Old 3rd November 2011, 04:40 AM   #29
rknize is offline rknize  United States
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Power it up with just the rectifier tube. If that is OK, add the input tubes. If that is OK, add back the output tubes, one at a time.
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Old 3rd November 2011, 06:43 AM   #30
Alco is offline Alco  United States
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thanks for taking an interest, Russ.

So here's as far as I got before the fear set in:
I pulled all the tubes,
plugged the amp into my little 300 watt variac,
and measured the voltages from the power xformer at 110 volts.
They were right on spec.
The power transformer is an Edcor xpwr163-120 B+=550V 150ma

I inserted the rectifier, the JJ GZ34 that had been in the amp when it was last working. I put a 1.5 amp fuse in the amp and brought the variac up to 110 volts. The filament began to glow and warm. Just at the point where I expect the B+ to come on line the fuse burns and I see the briefest small spark in the rectifier.

Thus chastened, I tried another rectifier, this time a chinese 5ar4 known good. With a fresh fuse in the amp I cranked the variac back up and again the filament warmed and as the B+ came on line the fuse burned, this time not just the 1.5 amp fuse in the amp, but also the 3 amp fuse in the variac.
No lightning in the tube, but it felt very hot for the short time it was on.

Thus chastened, I pulled the rectifier and went back to measuring the xformer voltages. Still right on spec. I've got a EMC 215 tester and both rectifiers still test good. It looks like I haven't destroyed anything yet, but I'm game to keep trying.

I think my power transformer circuit is working but thats about it right now.

What do you think I should try next ?

perhaps selling it in times square ?
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