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Old 23rd April 2012, 09:31 PM   #12271
Rixsta is offline Rixsta  United Kingdom
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Quote:
Originally Posted by AndrewT View Post
2mm to 5mm is good.
5mm to 30mm is getting a bit long.
Im using the ebay boards from jims audio. the resistors are actualy just over an inch from the Fets

Quote:
Originally Posted by AndrewT View Post
did you install an RF filter to the input of the F5?
No. sounds like a nice idea tho!

Last edited by Rixsta; 23rd April 2012 at 09:33 PM.
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Old 23rd April 2012, 09:32 PM   #12272
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Quote:
Originally Posted by zen mod
it's biased = drawing current , so bulb must lit and drop tooo much of mains

ditch bulb tester out and power up - without speakers,please

check bias and offset
'Bad' channel got the fuse blowing when I power up with a normal iec cord
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Old 23rd April 2012, 09:43 PM   #12273
Zen Mod is offline Zen Mod  Serbia
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desolder both jfets an mosfets and check them

simple as that and fastest
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Old 23rd April 2012, 09:49 PM   #12274
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Quote:
Originally Posted by studiostevus View Post
'Bad' channel got the fuse blowing when I power up with a normal iec cord
Ok... strangest things happening here:

I put down both trimmers P1 and P2 of the bad channel back to 0Ohm --> tested again with my last fuse and normal IEC cord --> Tataa... nice 47V supply power to the channel, of course 0 bias, and a little DC offset...

Then.. I though.. what the heck.. and I started adjusting the P1 and P2 trimmers... and guess what: I could just trim them to 0VDC offset and 0.5xxV bias... like nothing happened...

All of course on the bench with no speakers or preamp attached.
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Old 23rd April 2012, 10:12 PM   #12275
6L6 is offline 6L6  United States
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Perhaps the speakers are the problem? Do they work with other amplifier? (Just trying to eliminate unknowns)
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Old 23rd April 2012, 10:21 PM   #12276
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Uuhm yes!
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Old 23rd April 2012, 10:22 PM   #12277
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I have two 4ohm 20w resistors here... Would it be a good idea to test with those, or are there steps I need to take first?
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Old 24th April 2012, 09:00 AM   #12278
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I guess the question that i have really is:
1. I can re-bias the amp, does that mean that nothing was damaged?

2. It seems its working with no load. What could have caused smoke with load? Too high bias?
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Old 24th April 2012, 11:27 AM   #12279
JBdV is offline JBdV  Netherlands
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1. if you can rebias its very likely the amp to have survived the bad event (besides possible heat damage most likely on resistors without them being completely faulty)

2.what smoked?? Any damage visible? As long as the heatsinks didn't go beyond 60 degrees Celcius the bias should not have been too high.
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Old 24th April 2012, 11:50 AM   #12280
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Thanks

1. That's hopeful...There is no visible evidence of damage.

2. I had the lid on, so unfortunately i couldnt see what smoked.

I had already run the amp for 2-3 hours to warm up and bias. Then i unplugged it, carried it to the living room and hooked up the speakers and equipment. It had probably 10mins to cool down. Then i fired it up, started the preamp, and smoke appeared.... Probably within 10 or so seconds. Then i quickly shut it down... The heatsinks certainly were not 60 degrees
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