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Post subject: Supersonic 60 bias question
Posted: Mon Jul 30, 2012 8:41 pm
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Hey everyone, I recently picked up a supersonic 60 1x12 combo. I went to check the bias and found it cold from the factory. I have been trying to set it at 70% max dissipation, but based off a plate current of 470, I can't turn it up high enough. Anyone have any experience with this amp? Will it need a resistor changed or am I missing something?

Thanks!


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Post subject: Re: Supersonic 60 bias question
Posted: Mon Jul 30, 2012 9:23 pm
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Yeah, what you are missing is the fact that the plate VOLTAGE is about 470 VDC (B+ appears to be somewhere between 478 and 485 VDC). There is one bias pot (R156) and two bias test points to measure cathode current, one for each 6L6GC (TP49 and TP50). According to the schematic, each tube is set to 32 mA cathode current, which assuming a plate voltage of about 470 VDC is about 50% max plate dissipation. Plate voltage will drop as cathode current (plate current) increases. Based on the tube specs and the bias power supply, you may not be able to achieve 70%. My BDRI can only get to about 55%, while my 5F6A Bassman clone hits right at 70%.

http://support.fender.com/schematics/gu ... _Rev-A.pdf

Unless you know what you are doing, I don't recommend messing with the bias circuit. I would suggest getting a hotter pair of tubes.

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Post subject: Re: Supersonic 60 bias question
Posted: Mon Jul 30, 2012 9:48 pm
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Understood. I actually meant plate voltage, not current. just typing in a hurry. I saw that 32mA was the factory spec, so that's where I set it. I don't plan on messing with the bias circuit or getting tubes for now, it sounds alright. I was more curious to know if my experience was common or just my amp. Sounds like it's just they way they're made.


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Post subject: Re: Supersonic 60 bias question
Posted: Mon Jul 30, 2012 9:53 pm
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ccentola wrote:
Sounds like it's just they way they're made.


Yup.

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