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16th October 2010, 12:34 AM
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#1 |
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diyAudio Member
Join Date: Feb 2010
Location: calgary alberta tundra canada
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miniblok 1 voltage problem
i built this amp a while ago and all the voltages checked out, i had 215 volts B+ but now the voltage has bumped up to 250 for some reason and i cant determine why that is. i guess there isnt enough voltage drop across R1 so that means that the tube isnt pulling up enough current, im not sure where to go from here. maybe i can just increase the value of R1 but that doesnt really solve the mystery...
any ideas? thanks |
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16th October 2010, 01:17 PM
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#5 |
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diyAudio Member
Join Date: Jul 2008
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I guess if the tube's parameters are within optimum working levels then all should be ok?
Any change in current or sound? Has R2 or R3 drifted? Have you measured the cathode voltages/current? If R3 is pulling less current, the B+ is likely to rise. Last edited by Brit01; 16th October 2010 at 01:19 PM. |
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16th October 2010, 01:30 PM
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#6 |
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diyAudio Member
Join Date: Sep 2003
Location: Midland, Michigan
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The tube characteristics have changed for some reason. The output triode is pulling less current than it pulled originally. Perhaps it's gassy. Have you tried another tube?
__________________
Frank |
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16th October 2010, 01:55 PM
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#7 | |
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diyAudio Member
Join Date: Feb 2010
Location: calgary alberta tundra canada
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Quote:
could it be the bypass cap (c8) next to r3? maybe it's voltage rating is too low because i have the same problem with the other channel's amp. the sound has become distorted. im going to install a 1ohm resistor from the cathode to ground to measure current. |
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16th October 2010, 01:56 PM
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#8 | |
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diyAudio Member
Join Date: Feb 2010
Location: calgary alberta tundra canada
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Quote:
i tried a different tube and the result is the same. i guess ill just start switching out parts until i hit the fawlty component |
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16th October 2010, 02:08 PM
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#9 |
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diyAudio Member
Join Date: Sep 2003
Location: Midland, Michigan
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Is the bias voltage correct?
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Frank |
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