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Old 14th May 2012, 05:54 PM   #12321
6L6 is online now 6L6  United States
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Does removing the protection circuit change or affect the rest of the circuit at all? Will I need to re-bias?

It's not that replacing the devices is difficult, just that getting new ones is a headache... as I have no replacements on hand.
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Old 14th May 2012, 06:14 PM   #12322
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Quote:
Originally Posted by 6L6 View Post
Does removing the protection circuit change or affect the rest of the circuit at all? Will I need to re-bias?
......
nope
they're not in function while amp is idling

Quote:
Originally Posted by 6L6 View Post
...

It's not that replacing the devices is difficult, just that getting new ones is a headache... as I have no replacements on hand.
that's critical only when you're doing that for money , as day job
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Old 14th May 2012, 06:15 PM   #12323
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That fix doesn't make any sense. So what if the circuit ground is connected to the chassis? Something else is going on here.
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Old 14th May 2012, 06:22 PM   #12324
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I'm sure that something else was "chassised" , not tone gnd
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Old 14th May 2012, 06:24 PM   #12325
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Originally Posted by luvdunhill View Post
That fix doesn't make any sense. So what if the circuit ground is connected to the chassis? Something else is going on here.
I have thought that as well, but don't know where to start determining the problem...
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Old 15th May 2012, 12:22 AM   #12326
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Is the copper surrounding the PCB mounting holes actually going anywhere? From my faint memory of the boards I have used I thought there was just a doughnut of copper surrounding the holes and it didn't go anywhere (don't hold me to that). One F5 I built went funny in one channel and on the CRO with a sinewave in, one half of the sinewave was more compressed (rounded off) that the other. This gave a subtle distortion to the sound. That turned out to be one faulty FET in the input section. I assume that your rail voltages are both the same and and DC on the output is less that about 50mV.
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Old 15th May 2012, 12:36 AM   #12327
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They are the newest cviller boards, and no, the copper in the mount holes isn't supposed to be connected to anything!

Yes, the rails are both very close to 23.8 volts and the offset is almost zero.
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Old 15th May 2012, 12:57 AM   #12328
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I have never used those boards. Just JIM's and one other similar to JIM's. I assume you don't have access to an audio signal generator and a CRO so that doesn't make it any easier. I suppose all you can do is check all the components again, preferably out of circuit and maybe substitute some semiconductors from the board that is working. Regards.
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Old 15th May 2012, 02:07 AM   #12329
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Ok, here is a question for those if you much smarter than I -- (which is most everybody...)

Now that both channels are completed and the amp measures and biases normally, the channel that was shorted sounds a bit fuzzy. (it's subtle, but very much there.)
I am not smarter than anyone here, I can proof how dumb I am by all the dumb things I've done and had to fix.
The fuzzy sound, sounds like a bad solder joint, cold solder joint and it could be anywhere, even the ground wires.
Check all the solder joints and resolder any or all that have not bleed through to the other side of the board. Don't over heat though.
It could be a high frequency oscillation. Try adding (clip on) a small cap (100 pF) across feedback resistors or gate to output. To see if the fuzzy goes away. If it does, look for a reason why that channel is different than the other one. For that matter, do that anyway, look to see how it is different than the good one.
Keep looking for something and you will find something. It is frustrating until you find it, then very satisfying. You will feel like you know something about layout, soldering, oscillations, or whatever.
By the way, all the board help keeps you looking for the problem. In the old days, I just set the project aside and never figured it out, feeling lost with no one to ask. Hooray for these forums, well the internet in general.

Rush
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Old 15th May 2012, 04:21 AM   #12330
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They are the newest cviller boards, and no, the copper in the mount holes isn't supposed to be connected to anything!

Yes, the rails are both very close to 23.8 volts and the offset is almost zero.
I'm looking at my unassembled cviller v2.0 boards, and while the mounting holes are plated, they don't connect to anything else on the pcb...

Just curious, did you clean all the flux off?
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