UPGRADE: MANLEY Neo-Classic 300B PREAMPLIFIER 5/1/2003

PURPOSE: To lower noise level.

Serial numbers for units that will benefit from this update are:

3BMP000 – ALL; NEO3B036 –038, 040 - 047

UPDATE KIT INCLUDES:

a)      TWO 2 x 1000uF/63v + 0.1uF/250 capacitor banks

b)      TWO rubber feet

c)      10” of 2% silver solder

d)      Instructions and drawings for procedure

TOOLS REQUIRED:

a)      Phillips screwdriver

b)      Soldering iron

c)      Maybe a small pair of pliers to hold the wires as you solder them.

CAPACITOR INSTALLATION PROCEDURE:

1.      Turn off the preamp. Leave unit to cool off for 10 minutes.

2.      Assure the preamp power cord is unplugged from the wall!

3.      Take out all the tubes from the unit to avoid breaking them, since you need to turn the unit upside down. Label the tubes if you need to know which one went where if you are not sure. You can use a Sharpie marker if you’d like.

4.      Turn the unit upside down. Use something like a block of wood or some packing foam to support and keep the unit stable.

5.      Remove the bottom cover.

6.      Refer to the drawing for the location of the parts involved in the next steps. In the unit, locate the two 50 ohm/5 watt cathode resistors on the 300B tube socket. The heaters on the 300B tube are the two fat pins. The heater and cathode are the same thing as the 300B is a directly heated triode. See picture below:

7.      The cap update kit comes with 3 wires you will need to connect (per channel). One black (or green) wire (GROUND) and two red wires (or the positive capacitor leads as shown above) (HOT). The yellow arrows in the picture above show you where these six connections are.

8.      The black (or green) wire should go to circuit ground. The closest circuit ground point is the grounded side of the 820 ohm / 5 watt resistor. Each of the red (or the positive capacitor leads as shown above) (HOT) wires should go to one of the two heater pins. The best place to solder these wires is right at the top side of 50 ohm resistor wire leads.  It does not matter which HOT wire goes to which heater pin.

9.      See drawing or pictures to find the connection points for each of these 3 wires. Make these three connections. 

Click here for a closeup:

10.  Lay the capacitor banks down over the 300B tube socket pins. You can use the enclosed rubber foot to isolate the caps off the printed circuit board.

11.   Repeat for the other channel.

12.   Replace bottom cover, re-install tubes, and you are done! No further adjustment or alignment is necessary.

For further info or to order this kit, please contact our service department.
If you would like to send your unit in and have Paul perform this upgrade for you, please contact him at the address below:

Location of this page online: 

http://www.manleylabs.com/techpage/300BPreampCAPMOD.html