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Post subject: Temporarily locking the bias screw in place
Posted: Sun Dec 09, 2018 5:54 pm
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What's everyone using to keep the bias pot in place after rebiasing the amp. When I retubed and rebiased my amp, I saw that the Fender factory had used something like automotive touch-up paint or fingernail polish to set the pot in place.


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Post subject: Re: Temporarily locking the bias screw in place
Posted: Sun Dec 09, 2018 6:49 pm
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I try finger nail polish, do not work good to me or it is because is a very old nails polish ?
Old vintage amp pot do not need that. I don't know about Super Champ X2 amp pots


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Post subject: Re: Temporarily locking the bias screw in place
Posted: Mon Dec 10, 2018 1:50 am
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That's good to know on the fingernail polish. If I try auto touch-up paint, I'll let you know how it goes.

Thanks for your reply!


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Post subject: Re: Temporarily locking the bias screw in place
Posted: Mon Dec 10, 2018 5:56 am
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Post picture of this pot.


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Post subject: Re: Temporarily locking the bias screw in place
Posted: Tue Dec 11, 2018 2:01 pm
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Next time I take the chassis out of the amp, I'll take a picture. If you re-bias your own amp, you'll know what it looks like; just a potentiometer with a slotted screw that's flush on top with the rest of the pot so you can turn it left or right to adjust the current flow.

It's actually very simple to re-bias this amp yourself, as long as you have a multimeter and you remember to keep one hand in your pocket to prevent accidental shock/electrocution. Because this amp doesn't have a standby switch, the caps drain off each time you turn the amp off, so it's pretty safe, actually.


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Post subject: Re: Temporarily locking the bias screw in place
Posted: Tue Dec 11, 2018 2:21 pm
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How to bias any amps is not a secret for me :lol:

Your bias pot look close to this one ;
ImageCapture d’écran 2018-12-11 à 16.15.11

Super Champ X2 bias circuit;

ImageCapture d’écran 2018-12-11 à 16.13.05


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Post subject: Re: Temporarily locking the bias screw in place
Posted: Tue Dec 11, 2018 8:52 pm
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No. My bias pot doesn't look like the one in the picture.


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Post subject: Re: Temporarily locking the bias screw in place
Posted: Wed Dec 12, 2018 1:49 am
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johne1 wrote:
No. My bias pot doesn't look like the one in the picture.


I write it may look close.... Anyway i understand,

Look more than the second one than the first one here.

Image[url=https://flic.kr/p/2drxL15]


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Post subject: Re: Temporarily locking the bias screw in place
Posted: Wed Dec 12, 2018 8:06 am
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There are 2 common reasons why manufacturers paint some sort of locking stuff on components.

One is the obvious reason -- to prevent that part from moving/turning randomly due to vibration.

The other sneaky reason is tamper-proofing.

There are people who don't know how amps work, but still like to open up everything they buy just to see what the guts look like.

They see that doohicky and wonder what happens if they turn it. But they see a smear of paint locking the setting, and it gives them the strong impression they aren't supposed to mess with that thingy.


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Post subject: Re: Temporarily locking the bias screw in place
Posted: Thu Dec 13, 2018 5:37 am
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Howdy, neighbor! Love Field area of Dallas here.

Everything you said makes perfect sense.

I'm about to take my Super Champ out of town and try to use it in a bar gig, even though I have access to a Hot Rod Deluxe I bought and gave away. I love my little Super Champ. I plan on using the line out to the PA, just in case, but I'm also replacing the stock speaker with a Celestion G10 Gold alnico speaker, rated at 98db, which I suspect is about 3 db louder than the stock speaker.

I'm also thinking about opening up the amp in my hotel room and rebiasing it hotter, 44-50mV, to get a little more oomph out of it. I have JJ 6V6s in it, so they can easily handle the extra current. I'm using a JJ 803S in the phase inverter position. These little amps are hard on the phase inverter tube. The amp starts to cut out when the phase inverter tube is failing. I recommend replacing the PI tube every 6 months and the power tubes once a year. The Chinese Groove Tubes Fender puts in them are actually pretty decent, my only complaint is with the GT 12AX7. It's a bit harsh and fails early.

Eurotubes publishes the following in their retubing kit for the Super Champ X2 and XD.

"Fender recommends 40mV at the test point however we often bias these up to as high as 55 using the JJ 6V6S's."


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Post subject: Re: Temporarily locking the bias screw in place
Posted: Thu Dec 13, 2018 6:01 am
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40 mv ( mean 40 milli amp ) is for two tubes. and for 375 volts plate voltage ( fender schematic ) .
And it is good only for perfectly matched tubes

I will not bias more than 40 , you may destroy 6V6's tubes using amp at high volume.

What is the 6V6's plate voltage at your "home" ?
More plate voltage = less mv ( ma)

Biasing without knowing plate voltage is working like a blind


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Post subject: Re: Temporarily locking the bias screw in place
Posted: Thu Dec 13, 2018 9:15 am
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JJ 6V6's aren't true 6V6's. In some ways more like 6L6's stuffed into small bottles.

Eurotubes' bias recommendations are only for the JJ 6V6's they sell, not for other 6V6's.
------------------------
I've had amps with external bias testpoints and pots. For my ears, with those amps and a variety of tubes, bias wasn't a big deal. Never found a magic sweet spot where the amp sounded best, and the bias had to be very cold to make the amp sound bad.

So I just assume schematic plate voltage +/-10% and aim for 65% dissipation. Should be in a safe reasonable range whether the PV is a little high or a little low.


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Post subject: Re: Temporarily locking the bias screw in place
Posted: Thu Dec 13, 2018 9:42 am
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I bought my 6V6s from Eurotubes with the double mica plates. I've had Twin Reverbs biased hot for more oomph, but in the end they're still just loud and clean, and the tubes just wear out faster.

I'll probably rebias my Super Champ to about 44mV. I'm not trying to make it break up sooner, just trying to squeeze a little more headroom out of it.


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Post subject: Re: Temporarily locking the bias screw in place
Posted: Fri Dec 14, 2018 2:45 am
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johne1 wrote:
I bought my 6V6s from Eurotubes with the double mica plates. I've had Twin Reverbs biased hot for more oomph, but in the end they're still just loud and clean, and the tubes just wear out faster.

I'll probably rebias my Super Champ to about 44mV. I'm not trying to make it break up sooner, just trying to squeeze a little more headroom out of it.


Until tubes are bias very very cold, most of the time you will not have more headroom .


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Post subject: Re: Temporarily locking the bias screw in place
Posted: Sun Dec 30, 2018 7:22 pm
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I ended up NOT rebiasing the amp. What I did do was put the amp up on a folding dinner chair and push the front-end with either an EHX Soul Food pedal or an EHX Triangle Big Muff pedal. The amp was amazingly loud, easily out in front of the drums, bass, keyboard, and other guitarist. I never got the volume past 5, despite using the combo with its stock 10" speaker. The tone was fantastic! The pedals, which I had just gotten for the gig, pushed the amp and speaker into territory I'd not heard from it before. Probably 3 times louder than without the pedals.

For the next out of town gig I go do with my old band, I'm thinking of adding the Super Champ extension cabinet and a Radial Engineering Cab-Link unit to run both the internal 10" speaker and the external 12" cab. Combined it'll be running at 16 ohms, so, not sure what to expect but willing to find out.


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