Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Hoffman Turret and Eyelet Boards => Topic started by: EL34 on May 18, 2018, 03:05:17 pm

Title: Hoffman Bias Board 1
Post by: EL34 on May 18, 2018, 03:05:17 pm

This is a Fender AB763 type bias circuit
It is made with my 1/8th inch thick epoxy board and turret lugs

The board also includes spaces for the two 100 ohm artificial center tap heater circuit resistors

You could use this board if you don't have room for this circuit on the main board

I stock the drilled board with no lugs
And the board with the lugs installed on this page
http://hoffmanamps.com/MyStore/catalog/TurretBoard.htm (http://hoffmanamps.com/MyStore/catalog/TurretBoard.htm)

I also have the complete part list with all the parts on this page
You can add all these parts with one click or pick and choose what you want.
The parts list also includes the two #6 mounting screws, two standoffs and two nuts
http://hoffmanamps.com/MyStore/catalog/PartsListIndex.htm (http://hoffmanamps.com/MyStore/catalog/PartsListIndex.htm)


Here's some pictures of the board
I don't assemble these boards with the jumpers or the parts, you have to do that  :icon_biggrin:

Title: Re: Hoffman Bias Board 1
Post by: EL34 on May 18, 2018, 03:06:07 pm

And here is the layout diagram
You have to add 3 jumpers between the lugs
One jumper is at the end of the 100 ohm resistors
Two jumpers go to the bias pot legs as shown in the layout and my image below

Note that the intensity pot is not included in the parts list
It is only shown here so you know how to hook it up to the bias circuit

Title: Re: Hoffman Bias Board 1
Post by: EL34 on May 18, 2018, 03:17:37 pm

You may have to alter the 3 watt 470 ohm bias range resistor if you cannot get a good bias voltage sweep on the bia pot.
This would be something you do after the amp is up and running and you are ready to bias your power tubes

That and other amp build info is included in this document from my library page
http://el34world.com/Hoffman/instructions.htm