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Old 14th November 2012, 03:35 PM   #511
anilva is offline anilva  India
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Quote:
Originally Posted by Zen Mod View Post
make a break for few days

after that , go back and compare channels visually

then power up and compare them with DMM
Thanks. I think you are right. Having spent two full days on putting it together, I definitely need some rest.

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Originally Posted by buzzforb View Post
Bad jfet is easy. Test V drop across source resistors. Take voltage readings at various places, starting with FE. Report back. All this after taking a break, as ZM suggested. It is amazing how many mistakes I have found after taking some time away from a project.
Yes, I have a good identical channel to compare the readings. One more thing the jFets are at 8.7 mA IDSS and the supply voltage is 33.5 V DC per rail. Papa's article talks of 8 mA IDSS. I dread desoldering on a thick doubled sided PTH PCB.

Thanks.
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Old 14th November 2012, 03:39 PM   #512
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Is that Idss measured in circuit or before installation. Are both channels showing that Idss? That seems high for a degenerted BL grade. IT is possibly too high in terms of dissipation, but ZM may have more insight in this particular area.
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Old 14th November 2012, 04:14 PM   #513
anilva is offline anilva  India
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Is that Idss measured in circuit or before installation. Are both channels showing that Idss? That seems high for a degenerted BL grade. IT is possibly too high in terms of dissipation, but ZM may have more insight in this particular area.
IDSS rating given by spencer and is measured before the installation.
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Old 14th November 2012, 05:08 PM   #514
sangram is offline sangram  India
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Nice case, Anil

Bad input FET is what it might be. There was someone who had the exact same problem on the F5 thread and there were some questions on being able to set the bias with a busted jFET, but apparently it is possible.

I wouldn't worry about desoldering from a double sided board. Just snip off the leads and solder the new transistor on top of the pad (no need to go all the way through). Works when the holes won't open up. Mostly though, a hot iron (very hot) an bit of solder to get the flow going, and some solder wick does the job of opening up great for me. Never had an issue even with very tiny through hole components.

Good Luck, the amp looks nice!
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Old 14th November 2012, 05:59 PM   #515
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In circuit should measure between 5-6mA.
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Old 14th November 2012, 06:53 PM   #516
anilva is offline anilva  India
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Nice case, Anil

Bad input FET is what it might be. There was someone who had the exact same problem on the F5 thread and there were some questions on being able to set the bias with a busted jFET, but apparently it is possible.

I wouldn't worry about desoldering from a double sided board. Just snip off the leads and solder the new transistor on top of the pad (no need to go all the way through). Works when the holes won't open up. Mostly though, a hot iron (very hot) an bit of solder to get the flow going, and some solder wick does the job of opening up great for me. Never had an issue even with very tiny through hole components.

Good Luck, the amp looks nice!
Thanks Sangram. How is your Turbo build coming along. I saw the pictures of your cabinet.

First I will measure and compare the working and the problematic boards before I change any component. Surprisingly the amp biases very well.

Cheers.
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Old 15th November 2012, 02:26 AM   #517
sangram is offline sangram  India
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I have everything except the PCBs, and it's on hold till my home renovations are completed in December

Do eliminate any errors in the input circuit as well, track the signal before it hits the input stage. Small oversights could be the case here.
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Old 15th November 2012, 11:24 PM   #518
1MOR is offline 1MOR  United States
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Anyone do a recent purchase of Heat Sink USA 10.08 profile, care to comment on product flatness?

Apparently there has been a flatness problem in the past and HSUSA stopped production for a while to improve their process?
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Old 15th November 2012, 11:50 PM   #519
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IT is a problem, but only if yo plan to couple two sinks together and then mount to the coupling device. I am in the middle of trying this very thing, but find time a bit sparse.
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Old 16th November 2012, 01:15 AM   #520
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i have this sinks. got them summer of 2011. and have 2 side by side. i do not have any problem with flatness.
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