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Post subject: Hot Rod Deluxe Bias problem
Posted: Mon Jul 28, 2014 9:46 am
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Hey Guys I could use some help here.... I went to bias my amp this weekend and I could not get any reading from the bias test point. The multi-meter was getting reading2 from the tube pins directly so I know it was functional.

Any ideas what might be happening? The amp is brand new and visually I can find no damage any where or busted solder joints.

Is there another point which bias can be measured from?

Thanks

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Post subject: Re: Hot Rod Deluxe Bias problem
Posted: Mon Jul 28, 2014 10:13 am
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Be sure that the amp is ready to play, standby switch in play position, negative meter lead on chassis, meter set to mV DC.

An alternative method to check the bias, with amp off and unplugged from electricity, read the resistance of each half of the OT primary and note the reading. One half is from the red wire to the blue wire, the other half is from the red wire to the brown wire. Once the resistance readings are noted, turn on the amp, standby switch in play, let it warm up and read and note the DC voltages (around 4 VDC each half) at the same places that you read the resistances. Then use Ohm's Law, I = E/R, to get the current. The resistances of the OT primary halves will probably be somewhere close to 82 ohms and 112 ohms.

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Post subject: Re: Hot Rod Deluxe Bias problem
Posted: Mon Jul 28, 2014 10:27 am
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Thanks for the response.

I had the amp on and let it warm up for 30 minutes. Standby was on as well during checks. I was grounded on the chassis screw hole, and my multi mter was on its 200 mV read setting. I could get reading from various other points on the board. Just NOT from the designated test point.

I'll try your alternate way tonight.

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Post subject: Re: Hot Rod Deluxe Bias problem
Posted: Mon Jul 28, 2014 3:53 pm
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Did the amp work ? Sound to speaker ?
Output tubes seat well in their socket ?


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Post subject: Re: Hot Rod Deluxe Bias problem
Posted: Mon Jul 28, 2014 4:00 pm
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nssane wrote:
Hey Guys I could use some help here.... I went to bias my amp this weekend and I could not get any reading from the bias test point.

Thanks



Did you ever successfully adjusted the output tube's bias using this checkpoint ---in the past? If so, what mV values did you get?


Thanks!


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Post subject: Re: Hot Rod Deluxe Bias problem
Posted: Mon Jul 28, 2014 4:24 pm
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Yes some amp story might usefull


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Post subject: Re: Hot Rod Deluxe Bias problem
Posted: Tue Jul 29, 2014 7:55 pm
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Amp is new to me.
This was the first time I've tried to use the test point.

Amp does have sound but seems to break up very early on the cleans which is why i wanted to verify the bias.

There is not much story to be told. It a stock Fender HRD

Tubes are all seated tightly with no rattles or buzzing and no obvious signs of any board damage

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Post subject: Re: Hot Rod Deluxe Bias problem
Posted: Wed Jul 30, 2014 1:25 am
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If your voltmeter work as you write , if you can't have a reading on the bias test point

1- You have a bad contact with meter ; positive probe on test point or / and negative probe pn amp ground.

a) test point is "dirty "; use sand paper , file ........
b) you are not connected to the amp ground
c) you don't use the right test point
d) you forget ( to tell us ) something :(

That's all :lol: check all my statements until you find.

Good luck


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