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F5 V3
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Old 14th January 2020, 04:38 AM   #361
pfarrell is offline pfarrell  United States
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Join Date: May 2019
Location: Kingston, NY
Fried amp update:

- Mosfets replaced—and smoked resistors... Everything fastened down with fancy nylon washers.
- Powered on with bulb tester and 3 DMMs connected—no surprises.
- Powered on without bulb tester and 3 DMMs connected—Not getting any response from R7 and R8 via P1, P2 (zeroed before startup).
- Verified PSU output just to cross something off the list. 26.5VDC+/-

I am able to fiddle P2 and see some DC offset—but getting zero voltage across both resistors regardless of how many turns.......hmmmmm.
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Old 14th January 2020, 07:01 AM   #362
AudioSan is online now AudioSan  Norway
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I think you may want to check your J-fet's.
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Old 14th January 2020, 11:34 AM   #363
Dennis Hui is online now Dennis Hui  Canada
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Location: Toronto, Canada
F5 V3
Please check the voltages across the 10 ohm resistors R3 and R4.

Can you also measure the voltages you can get across R5 and R6 as you
crank up P1 and P2?
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Old 14th January 2020, 01:28 PM   #364
airborne11b is offline airborne11b  United States
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Quote:
Originally Posted by pfarrell View Post
Fried amp update:

- Mosfets replaced—and smoked resistors... Everything fastened down with fancy nylon washers.
- Powered on with bulb tester and 3 DMMs connected—no surprises.
- Powered on without bulb tester and 3 DMMs connected—Not getting any response from R7 and R8 via P1, P2 (zeroed before startup).
- Verified PSU output just to cross something off the list. 26.5VDC+/-

I am able to fiddle P2 and see some DC offset—but getting zero voltage across both resistors regardless of how many turns.......hmmmmm.
Similar thing happened to me in one of my monoblocks. I had the P jfet in the N jfet spot and the N jfet in the P spot. Because i used a variac and low voltage, nothing was fried. I swapped them and everything was as it should be. Moral of the story, double, triple check your stuff before moving forward.
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Old 14th January 2020, 02:02 PM   #365
pfarrell is offline pfarrell  United States
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Join Date: May 2019
Location: Kingston, NY
Quote:
Originally Posted by AudioSan View Post
I think you may want to check your J-fet's.
Yes... elephant in the room! Toshiba's...


Quote:
Originally Posted by Dennis Hui View Post
Please check the voltages across the 10 ohm resistors R3 and R4.

Can you also measure the voltages you can get across R5 and R6 as you
crank up P1 and P2?
Yes! I will report back!


Quote:
Originally Posted by airborne11b View Post
Similar thing happened to me in one of my monoblocks. I had the P jfet in the N jfet spot and the N jfet in the P spot. Because i used a variac and low voltage, nothing was fried. I swapped them and everything was as it should be. Moral of the story, double, triple check your stuff before moving forward.
This was a working amp... For the last few months... Then had a catastrophic failure a couple of weeks ago due to a metal washer on the lower PCB mounting holes biting through the solder mask and making contact with the trace...

Thanks guys!
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Old 15th January 2020, 04:01 AM   #366
flamethrower1 is offline flamethrower1  United States
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F5 V3
Sorry you are going through some "set backs" pfarrell, mine came early.
Just got to keep on going forward because the other option sucks.
This amp still amazes me with the sound it produces.
Any time I light it up, it turns into a non stop "I want to hear this next" kind of thing.
And all of it is better sounding than anything I have had before.
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Old 15th January 2020, 04:38 AM   #367
pfarrell is offline pfarrell  United States
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Join Date: May 2019
Location: Kingston, NY
Thanks for the support!

The decision was made today after some further testing and consultations to pull the board and frame it alongside the working channel—yes, I will fab a shadowbox and mount them heroically. I even put back the blown mosfets in all their glory—btw the jfets tested fine.... It will be great. I have procured some replacement already built boards a friend offered up. Which is incredible. So the F5 will live again!

That said... when the F5 boards were offered, it was noted that “...nobody who’s ever built an Aleph J has ever missed their F5...” Haha.

So when does that build start flamethrower? I have to say he’s likely right....also the whole experience was very insightful, more practice with everything, and less dramatic because I have the AJ running daily...
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Old 15th January 2020, 05:21 AM   #368
6L6 is offline 6L6  United States
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F5 V3
No, I said, “it’s uncommon for people that have built both to prefer the F5.” Not “nobody”. They are both incredible amps and I’d be happy to have either as my one and only amp.

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Old 15th January 2020, 12:51 PM   #369
pfarrell is offline pfarrell  United States
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YES! Perfect opportunity for a moment of GRATITUDE.

I couldn't have done any of this with any kind of grace without this forum and some seriously generous and passionate people. It's a testament to Nelson's generosity and grace and those gifts keep giving and providing incredible grounds for all of our exploration. Really, more than amps...

F5? Saved by another great guy we all couldn't explore without—and I like many (most?) will probably end up building all of these amps in one form or another on my search AND then rotate them in and out of use just to experience the ride.... and there's no real end anyway. —but there are some incredible builds you all have made.

Can't love the AJ (or the F5) without each other.
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Old 15th January 2020, 02:30 PM   #370
Dennis Hui is online now Dennis Hui  Canada
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Location: Toronto, Canada
F5 V3
The AJ and F5 will make for a nice comparison/contrast.

And you'll likely build more and rotate them, and find you use some more than
others.

But for me, even the ones I don't use as often are amps that I would be happy
with for long term use. These designs don't disappoint.
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We are fearless amplifier builders. A little heat doesn't scare us at all.
- NP 2002
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