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-   -   Swordfishy/ASPEN FETZILLA power amp (http://www.diyaudio.com/forums/aksa/191053-swordfishy-aspen-fetzilla-power-amp.html)

keantoken 30th September 2012 04:40 AM

As arm as it should for being biased at 150mA. I didn't measure it. There as a time it got hot due to oscillation but not after I fixed it.

I didn't do the cap shield trick ith Fetzilla, in case you misunderstood.

AndrewT 30th September 2012 09:03 AM

Syk,
your FetZilla will run too hot because your heatsink is the wrong shape, the wrong size, in the wrong orientation and is far too thin.

Choose a proper heatsink for the duty !

syklab 30th September 2012 09:23 AM

Quote:

Originally Posted by AndrewT (Post 3184504)
Syk,
your FetZilla will run too hot because your heatsink is the wrong shape, the wrong size, in the wrong orientation and is far too thin.

Choose a proper heatsink for the duty !

Hi Andrew,
Currently this is the largest heat sink available from the local store here in HK , it measures 12" x 4.5" x 1.25". I will order a set with case after the golden week holiday, will you kindly help to determine what will be the proper type and size ?

Thanks

AndrewT 30th September 2012 09:27 AM

assume a Ta and Ts for the dissipation you need.
From there you can determine the required Rth s-a to which you have applied the necessary deltaT de-rating.

But you must ensure that your de-rating takes account of the thickness of the backplate. This is not usually specified by the heatsink manufacturer due to the way they all assume isothermal conditions for the entire backplate area.

meanman1964 30th September 2012 09:48 AM

Mine runs after hours between 38 and 41 and can keeps my hands on the sinks the hole time.

syklab 30th September 2012 10:15 AM

Quote:

Originally Posted by meanman1964 (Post 3184562)
Mine runs after hours between 38 and 41 and can keeps my hands on the sinks the hole time.

I can touch it butting is quite warm.

syklab 2nd October 2012 09:34 AM

Something bad just happened.
http://i1196.photobucket.com/albums/...b/R0020472.jpg

http://i1196.photobucket.com/albums/...b/R0020476.jpg

Both channels were working fine on the start-up test before I put them in a temporary case except being a little hot. Today I put them both in a case and connect to a power transformer. After I switch-on the power, a not too loud hum and spark came off from both PCB, it looks like R22 and R24 were blown but everything else looks ok, the fuse still ok. I examine the wiring and discovered that ( I am using only one transformer, a 2 x 26VAC 250VA R-Core) the V+ AC input from left channel and the V- AC input were connecting to the same secondary winding. Could this be the cause to the blown resistors ? What to do next?

ajst2duk 2nd October 2012 10:23 AM

Pretty hard to get the magic smoke back in those little resistors.

smartx21 2nd October 2012 10:24 AM

Am I wrong, or you were running out of solder when setting those elcos?

syklab 2nd October 2012 10:32 AM

I intentionally use less solder there so that I can replace those caps easy later on. R22 and R24 will be replaced.


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