# Hot to bias 68 Bassman AA864



## SteveRayVaughan (Dec 18, 2010)

Hello, does anyone know how to bias a drip edge AA864 Bassman? The plate voltage is 460. I've read that one tube is fixed and other is adjustable...I've also read "Don't" use the adjust for the lowest hum method...

Any thoughts out there?

Many thanks!


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## SteveRayVaughan (Dec 18, 2010)

Here are a few pics...

Pictures by TheStevieRayVaughanExperience - Photobucket


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## WCGill (Mar 27, 2009)

That's the straight bias voltage circuit, not the hum adjust. This is the same amp images of which were posted below by someone else wondering if it was AB763.


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## stratele52 (Oct 25, 2010)

This pot is for bias adjustment AND is for the two tubes. I understand that youre are sure you read/or do right bias in your other post.
How you'll read the bias milliamp on 6L6's cathode , the pin number 8 ?
You have a bias probe or solder 1 ohms resistor.

Hum method is not good

Go to You Tube and search : amp tubes bias, you'll see many videos. But don't forget: lethal voltage in the amp can kill you


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## SteveRayVaughan (Dec 18, 2010)

Hi and thanks for the reply. Yeah the pics were posted by the guy I bought the amp from. I'm assuming, according to Wild Bill that it's an AA864 circut that's had some updating. I just boased my Vibroverb and was hoping that s imilar method would work for this Bassman...I'm not sure how to measure the ma's on this guy...I think another reply suggested pin 8...I'll look into it.
Thanks!


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## SteveRayVaughan (Dec 18, 2010)

Thanks! I'll give that a try...
Cheers!


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