Bassman Reissue w/ Hoffman 5f6a rebuild power tubes

[Jacobjohn]

Hello everyone. New here. I recently purchased a 90’s bassman reissue (not Ltd version) that has a complete ptp rebuild done by Hoffman in 95. It was changed to 5f6a specs but with an added master volume and higher gain “Marshall” sounding channel.

I need to replace the power tubes. If I replace the tubes with a matched pair of the same kind of tube (6L6GC) is there a biasing thing I have to do? Also, how would I do that? There’s no mark on the board that I can see that says anything about adjusting or testing bias.

Also any recommendations for tubes?

Thanks everyone!

[shooter]

with NO power tubes installed;
put your black lead on chassis
put your red lead on one of the power tubes pin5 and measure the negative VDC
assuming you have -xx, probe other pin 5, should be close to same.
now adjust bias pot to one end, record, adjust to other end record, set back to ORIGNINAL setting and post values

[sluckey]

read...

     http://www.duncanamps.com/technical/lvbias.html

[Jacobjohn]

Ok so my question is:
Do I need to bias if I replace power tubes in this amp with same kind of power tubes?
If so, where is the bias pot adjustment thing?

[sluckey]

Yes. The bias pot is that white thing next to the two blue caps on the board. There are also two 1 ohm resistors on the board. You may want to let someone else do this for you.

[Jacobjohn]

Are the 1 ohm resistors something that needs to be messed with as well when biasing new power tubes?

[shooter]

 
only if you want to know if the tubes will melt or freeze

[sluckey]

Are the 1 ohm resistors something that needs to be messed with as well when biasing new power tubes?

Did you read and understand the link I posted above? You may want to let someone else do this for you.

[drew]

Pay particular attention to the "Safety Advisory" section of that link, which is about 2/3 of the way through the page.

[punkykatt]

Jacobjohn, do you live near Sarasota Florida?

[Jacobjohn]

Jacobjohn, do you live near Sarasota Florida?

No I’m in Seattle