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Post subject: 1993 Fender Super Amp Bias
Posted: Sat Mar 31, 2018 3:26 am
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Looking for help on my 93 Super Amp Bias about to do a Tube change

Schematic in link

https://imgur.com/gallery/wvKyv


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Post subject: Re: 1993 Fender Super Amp Bias
Posted: Sun Apr 01, 2018 1:37 am
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Location: Province de Québec, Canada
You may have to play with R104 and R103.

R104 first ; higher value = more negative voltage = colder bias
lower value = less " " = warmer bias

R103 ; short answer; only if you can't have right voltage with R104

You can built a ajustable bias
Use the ( One control circuit ) show here;

25K pot wiper mut go to C41
Pot value and 22 K value are a average, you can use other value not to far.

http://hiwatt.org/Schematics/BiasCkts2.gif

Another version of the circuit;
http://education.lenardaudio.com/en/13_ ... mps_4.html

__________________________________

In both mod ; Test you circuit with no Output tubes in circuit.

1- Before any mod, read you negative voltage a each Power tubes grid pin
Tubes plug and tubes not plug ; should be same ore very close

Keep Power tube remove from the amp

2- Do the mod
3- Read voltage at each tubes grid

4- If bias look safe , put power tubes in the amp , fine tune bias


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Post subject: Re: 1993 Fender Super Amp Bias
Posted: Sun Apr 01, 2018 9:39 pm
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Is it better to add the pot as a variable resistor or as a voltage divider


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Post subject: Re: 1993 Fender Super Amp Bias
Posted: Tue Apr 03, 2018 9:50 am
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stratele52 +1
First I'd like to thank stratele52 for his great reply with diagrams on how to do it. He's number one tech, always helpful. TimsA is good too, just kidding, TimsA is great too and all the others that contribute to the posts in a technical response. Seem like all the time it's really useful information weather the Original-Poster OP can use it or not. I like reading the posts.

If I did the adjust bias, seems like I'd want the selected - Vbias setting to be in the center of the adjustment range. That way it would cover the setting, you could adj +/- from your setting. So if you use the voltage divider or variable resistor, centering the pot might require different values of resistors. If you use an adjustment pot that's too big in resistance value just small adjustments would have a larger change in the -Vbias, were as a lower pot value would have less adjustment sensitivity. And the type of pot to use is a consideration. I'm not really saying much here, just thought I'd reply,,lol. Nothing wrong with copying a schematic design, keep it to yourself. Voltage divider or variable resistor, don't know if it matters that much, unless the current is a factor or reliable of a stable -Vb setting is required.


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Post subject: Re: 1993 Fender Super Amp Bias
Posted: Tue Apr 03, 2018 1:17 pm
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jackhammer wrote:
stratele52 +1
First I'd like to thank stratele52 for his great reply with diagrams on how to do it. He's number one tech, always helpful. TimsA is good too, just kidding, TimsA is great too and all the others that contribute to the posts in a technical response. .



Thank's but IMO I'm a average tech and TimAudio is the master


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