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Old 16th April 2011, 02:37 PM   #1
mjock3 is offline mjock3  United States
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Default Distortion in amp after warm up

I have a Sonic Frontiers SFC-1 integrated amp. Once it warms up pretty well it distorts out of one channel when played at moderate levels. At low levels all seems fine. Any ideas what would cause this?

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Mark
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Old 16th April 2011, 03:02 PM   #2
adason is offline adason  United States
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have you swapped the tubes between channels? to see if the distortion follows certain tube?
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Old 16th April 2011, 03:22 PM   #3
mjock3 is offline mjock3  United States
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No I will give that a try. I was wondering if tubes or bias could cause that.

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Old 16th April 2011, 07:16 PM   #4
DF96 is offline DF96  England
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Yes, tubes or bias (or leaky caps?).
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Old 28th April 2011, 08:06 PM   #5
mjock3 is offline mjock3  United States
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I have swapped the tubes and it did not change anything. Have also checked bias and all looks well there. How would I go about checking for leaky capacitor?

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Mark
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Old 28th April 2011, 09:03 PM   #6
DF96 is offline DF96  England
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Check the grid voltage on the next stage. If the coupling cap is leaky then the grid voltage will rise.
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Old 28th April 2011, 09:09 PM   #7
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Check the sockets pins to see if they are dirty/corroded. Could also be a resistor or cap that is changing with heat.
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Old 29th April 2011, 07:33 PM   #8
wa2ise is offline wa2ise  United States
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Old high resistance value resistors have been known to drift to higher resistance. resistors like 470K going to 700K or more. Enough to cause distortion, even with perfect vacuum tubes. With the power off, measure each resistor to see if it's within its marked tolerance value.
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Old 29th April 2011, 07:39 PM   #9
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Quote:
Originally Posted by wa2ise View Post
Old high resistance value resistors have been known to drift to higher resistance. resistors like 470K going to 700K or more. Enough to cause distortion, even with perfect vacuum tubes. With the power off, measure each resistor to see if it's within its marked tolerance value.

Make sure you dissconect one lead of the resistor from the rest of the circuit during you check.
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Old 29th April 2011, 08:34 PM   #10
wa2ise is offline wa2ise  United States
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Quote:
Originally Posted by diesel_tech View Post
Make sure you dissconect one lead of the resistor from the rest of the circuit during you check.
Of course, but if you have the schematic, and you see that one end of the resistor only connects to a tube element (grid, plate or cathode) and also a capacitor, but no other resistors or coils, you won't need to.
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