Shared Projects by bax

Spike protection diode string for tube amps

Bias circuit for Ampeg B-15N.

Neutrik combo adapter round V1.2

The round board is the same diameter as the connectors barrel. The wires are first soldered to the board, then the board installed on the speakon connector. The entire assembly can then be installed on the chassis or cabinet. The installed wires should not protrude beyond the back surface of the board as the board sits flat on the connector.

Neutrik combo adapter square V1.2

Board must be installed after the Neutrik connector is installed on the chassis or speaker cabinet. The larger form factor over the round version of this board allows for easier connection of the wires to the board.

Ampeg 1974 B-15N bias pot

Bourns 3250W-1-203 this is a multi-turn, 20K linear taper pot. A 25KL such as a 3296W-1-253 will work as well. The required pin spacing is 0.1".

The total target resistance with the pot and serially connected resistor is 47K ohms. The design allows for either a single or a pair of parallel resistors to be used. You can use one or two 1/2W or two 1/4W resistors. The resistor pad footprints have a 10mm pin spacing. I prefer to use metal film resistors but this is not a requirement.

Different parallel combinations of resistors can be used to attain a resistance that gets you in the desired range. There are many possibilities. For example, two 75K ohm 1/2W resistors can be used such as Vishay-Dale CMF5575K000FHEB. Alternatively a single 33K ohm 1/2W resistor such as Vishay-Dale CMF5533K200FHEK can be used. These are available from Digi-Key. It is easier to find a pair of 75K ¼W resistors with a 10mm or less pad spacing.