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Old 3rd August 2012, 11:18 PM   #11
6L6 is offline 6L6  United States
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I am assuming that the photos posted were taken at a time before it blew up?

If so, please take some (well-lit, in focus) photos and post them here. You will be flabbergasted by what some guys can see in a photo!!
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Old 3rd August 2012, 11:29 PM   #12
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The case looks like its worth a small fortune.

Generally speaking the amp is nicely made.

I see R6 is missing - this is a feedback resistor that is in parallel with R8.

Testing a variation of an F5 with a sinewave generator
all full output - those Feedback resistors got bloody hot.

If the maker left F.B. resistors out - the other F.B. resistors could have been cooked.
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Old 3rd August 2012, 11:29 PM   #13
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One could install an AC coupled input on the rear of the amp...

But the issue well could be a parasitic oscillation in the second signal source... not DC offset.

but BOTH channels blew out??

that would be very unusual, which means that likely the fault is at the output end of the preamp/source thingie... a scope would tell all...

_-_-bear

Although... it is possible that the SOA of the output devices was exceeded due to the load, and it took 4 hrs to get the mosfets overtemp enough to go into thermal runaway and smoke?

PS. wow, the builder cuts 45 deg bevels in an aluminum block using a table saw!! very brave.
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Old 4th August 2012, 03:58 AM   #14
ra7 is offline ra7  United States
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Did you plug the new pre in without turning off the f5?
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Old 4th August 2012, 04:05 AM   #15
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If you zoom in fully on the second picture, there's a big brown spot on the right MOSFET to the left of the mounting screw. It could just be a camera artifact, or a blown transistor. Does the black plastic housing look brown and bubbly in the flesh?

- Eric
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Old 4th August 2012, 06:47 AM   #16
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Hi!

I know it's a little bit OT, but where can I get those nice small boards for the F5?
I've seen them a few times since my built is finished.

BTT, I think if both channels are blown up, maybe the problem is somewhere in the AC-DC-supply-section?

regards,
matthias
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Old 4th August 2012, 10:19 AM   #17
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it is peter daniels boards. send him a PM
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Old 4th August 2012, 11:07 PM   #18
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In the center photo, whats the wire going across the left mosfet then glued (red glue) to the heat sink?

Also, the power resistors look a bit stressed, again on the left side. This could be the photo quality.
They look like mine right before they crumbled.
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Last edited by vdi_nenna; 4th August 2012 at 11:11 PM.
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Old 4th August 2012, 11:14 PM   #19
6L6 is offline 6L6  United States
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Quote:
Originally Posted by vdi_nenna View Post
In the center photo, whats the wire going across the left mosfet then glued (red glue) to the heat sink?
That is most likely the temperature probe for the thermal monitor on the front.
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Old 5th August 2012, 01:12 PM   #20
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Quote:
Originally Posted by AudioSan View Post
it is peter daniels boards. send him a PM
Thank you very much, PM'd.
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