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PostPosted: Sun Jan 20, 2013 9:49 pm 
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Joined: Wed Jan 02, 2013 8:18 pm
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Hey,

The bias voltage on my Triwatt is about 10x greater than It should be, and the power tubes start glowing cherry red a few seconds after the power switch goes from Standby to Power.

The other voltages all make sense so far.

If anyone could shed some light on the the situation that would be great.

Thanks in advance.


Jon


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PostPosted: Mon Jan 21, 2013 12:39 am 
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Holy Ghost
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Location: Canada
FiRst check the value of the bias resistors, then the bias ciRcuit e.g the orientation of the diodes and filter caps for the bias circuit. Remember, the bias supply circuit needs to put a negative voltage out.

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PostPosted: Mon Jan 21, 2013 5:14 pm 
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Experienced
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Location: Vancouver B.C. Canada
coco wrote:
FiRst check the value of the bias resistors, then the bias ciRcuit e.g the orientation of the diodes and filter caps for the bias circuit. Remember, the bias supply circuit needs to put a negative voltage out.

That's right , and if you had a bias 10x normal, that much negative voltage on the grids should have turned the tube totally off.


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PostPosted: Tue Jan 22, 2013 10:29 am 
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It was the voltage at the test points that was to high. On the third time checking everything I discovered that I missed the jumper between the 620k ohm and 180k ohm resistor. That triple check is key!

All is now in order.

Now all I have to do is wait for my Marshall 1974CX 1x12 cabinet to show up so I can play it! :D

Jon


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PostPosted: Wed Jan 23, 2013 12:26 am 
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Holy Ghost
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Meaning it biased up and tested OK? Or you have to wait just to test it?

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