Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: frpax on November 17, 2018, 11:00:02 pm

Title: Help biasing a Hoffman 5F6A?
Post by: frpax on November 17, 2018, 11:00:02 pm: I searched the boards and really couldn't find what I am looking for, so here I am (again) asking probably silly questions!

OK, so I got my 2x12 Hoffman 5F6A all together and I want to bias the power tubes.
AND, I do not have one of those nifty biasing devices. Just a multimeter.

I had a friend help me with this on my first amp (Plexi 6V6), and I didn't have any of those biasing devices then, so I know it can be done.

I just need someone to walk me through it or point me to a thread that explains how to bias with just a multimeter.

Thanks for any help!!
Title: Re: Help biasing a Hoffman 5F6A?
Post by: sluckey on November 17, 2018, 11:35:13 pm: Read this...

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

All you need is a meter and a calculator. The 1Ω resistors are already installed on the Hoffman 5F6A board.
Title: Re: Help biasing a Hoffman 5F6A?
Post by: frpax on November 19, 2018, 10:15:37 am: Quote from: sluckey on November 17, 2018, 11:35:13 pm
Read this...

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

All you need is a meter and a calculator. The 1Ω resistors are already installed on the Hoffman 5F6A board.
Thank you!
Title: Re: Help biasing a Hoffman 5F6A?
Post by: frpax on November 26, 2018, 05:00:42 pm: Quote from: sluckey on November 17, 2018, 11:35:13 pm
The 1Ω resistors are already installed on the Hoffman 5F6A board.
Where?
Title: Re: Help biasing a Hoffman 5F6A?
Post by: Willabe on November 26, 2018, 05:19:43 pm: Quote from: frpax on November 26, 2018, 05:00:42 pm
Quote from: sluckey on November 17, 2018, 11:35:13 pm
The 1Ω resistors are already installed on the Hoffman 5F6A board.
Where?

On Doug's layout drawing, 5F6A, their by the power tubes, black wire runs from pins 1 and 8 back to the turret board, 1ohm R's.
Title: Re: Help biasing a Hoffman 5F6A?
Post by: frpax on November 27, 2018, 10:40:02 am: Quote from: Willabe on November 26, 2018, 05:19:43 pm
Quote from: frpax on November 26, 2018, 05:00:42 pm
Quote from: sluckey on November 17, 2018, 11:35:13 pm
The 1Ω resistors are already installed on the Hoffman 5F6A board.
Where?

On Doug's layout drawing, 5F6A, their by the power tubes, black wire runs from pins 1 and 8 back to the turret board, 1ohm R's.

Ah yes! I see them now. Many thanks
Title: Re: Help biasing a Hoffman 5F6A?
Post by: shooter on November 27, 2018, 10:53:06 am: Quote
Same voltage reading. 370-ish
fixed bias changes G1 vdc, pull PA tubes, put meter 'tween G1 and ground and measure -vdc, rotate pot ccw read, rotate pot cw read