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Build is almost finished, but there is a problem.

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Jon

Post subject: Build is almost finished, but there is a problem.

Posted: Sun Jan 20, 2013 9:49 pm

Joined: Wed Jan 02, 2013 8:18 pm
Posts: 2

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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coco

Post subject: Re: Build is almost finished, but there is a problem.

Posted: Mon Jan 21, 2013 12:39 am

Holy Ghost

Joined: Sun Mar 13, 2005 4:10 pm
Posts: 7519
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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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

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Stoo

Post subject: Re: Build is almost finished, but there is a problem.

Posted: Mon Jan 21, 2013 5:14 pm

Experienced

Joined: Sat Jul 22, 2006 2:59 pm
Posts: 480
Location: Vancouver B.C. Canada

coco wrote:

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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Jon

Post subject: Re: Build is almost finished, but there is a problem.

Posted: Tue Jan 22, 2013 10:29 am

Joined: Wed Jan 02, 2013 8:18 pm
Posts: 2

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!

Jon

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coco

Post subject: Re: Build is almost finished, but there is a problem.

Posted: Wed Jan 23, 2013 12:26 am

Holy Ghost

Joined: Sun Mar 13, 2005 4:10 pm
Posts: 7519
Location: Canada

Meaning it biased up and tested OK? Or you have to wait just to test it?

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Stephen
Web: www.trinityamps.com. Facebook: facebook.com/trinityamps. Twitter: @trinityamps

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