DD-30

This build guide is written assuming you already know how to build amps and just need a good layout.  Lets start with punching the chassis.  The chassis is a standard Hammond aluminum 16x8x2 chassis.  Starting with the top, draw a line 2" from the back of the chassis and 1.5" from the front of the chassis.  Tubes will be mounted on the back of the chassis.  Starting from right to left, mark the position of the first preamp tube 1.5" from the right edge of the chassis.  From there, position the remaining four tubes 2.25" from each other.  Notice the holes already drilled.  These are the mounting holes.  I have a bottom cover I use as a template so I drill these first.      




Next punch the holes for the tube sockets.  Once that is done, it is time to position the transformers and can caps.  Can caps are centered on the line and with the second and last tube socket.  The output transformer's mounting holes are on the line and centered between the can caps.  The power transformer is mounted close to the edge and centered between the two lines.  Toneslut's PTs have all the wires exiting one side of the PT.  The hole for the wires is positioned on the tube side so I have a short, straight run for the heater wires.  This greatly reduces heater induced hum.  Using any other PT, position the heater wires on the tube side.  Another trick I use to reduce hum is to use a 110v pilot light.  This greatly reduces the length of the heater wires.  The finished amp should only have a very small amount of hum with the gains and volume dimed.




Next is the front panel.  All holes on the front panel are centered 1" 1/8" from the bottom of the chassis.  This gives a little extra room for lettering.  The input is centered 1" from the left.  The remaining pots are centered at 1.25" intervals.  The holes are 3/8".  Input, Gain1, Gain2, Treble, Mid, Bass, Presence, Volume. 

I center the pilot light 1" 1/8 from the edge of the chassis.  The extra 1/8 is because I use a standard Fender jewel light and the hole for the pilot is big, 11/16," and I don't want it too close to the edge.  The power switch is centered 1"1/8" from that and the standby 1" from the power switch,  Holes are 1/2 ." 




Next is the back panel.  The back panel is pretty straight forward.  All holes are centered 7/8 from the bottom of the chassis.  This allows a little extra room to mount things under the jacks, etc. when necessary.  The fuse is positioned 1" from the edge.  The AC inlet is centered 1" 3/4" from that.  The impedance switch is centered between the power tubes or about 6" 5/8" from the left edge.  The two output jacks are centered 1.5" from the switch and each other.




The next step is to position the turret board.  The turret board is centered between the can caps and tube sockets about 1/2" from the input edge of the chassis.  Drill the holes for the stand offs and install them, then set the board aside and install the transformers and hardware.  

Here is the finished chassis with the transformers and hardware mounted.  Plenty of room with a 16" chassis but not a lot of extra space.




Next wire up the transformers and heaters.  Notice the straight run of the heaters.  Again, this greatly reduces the potential for unwanted noise.  The resistor going to the pilot is 100r.  My line voltage usually runs 120v and the pilot lights would fail after only a few weeks.  The resistor lowers the voltage to the pilot to about 102v so they last longer.  The yellow wire hanging out of the chassis at the bottom of the picture is the negative feedback wire attached to the 8r OT lead.  OT wires run between the power tubes so they are well away from preamp tubes.




Now it is time to mount the board and wire it up.

Preamp tube wires are red for B+, white for signal, and blue for cathode grounds.  The two signal wires going to the first stage are shielded and have the 10K grid stoppers mounted on the socket.  The shielded signal wire going to the 4th stage has the 47k grid stopper mounted on the socket.  Keep signal and cathode grounds well away from the B+ wires.  I bring the B+ wires over to the socket then go straight down to the socket pin.




Here is a picture of the power tube  and phase inverter wiring.  Notice the 1m grid stopper on the PI.




This is a closeup of the tone stack wiring from an earlier build.  Standard Bassman tonestack except for the 25k mid pot.  Notice pin one is not used on the bass and mid pot.  Tonestack wires go up and over the B+ rail.  Get too close and it will squeal.  You may be tempted to ground the shields to the back of the pots.  Don't.  It seems to remove any advantage from shielding the wires and makes the amp more prone to squealing.  Instead, ground the shields to the ground wires of the pots.  This connects the shield wires to the buss and avoids ground loops. 




Here is a picture of the turret board fully wired.  Bring signal wires up and over the B+ wires by at least 1/2" to avoid squealing, even the shielded ones.  The PT, OT, and 20/20/20/40 can cap are grounded to the 100/100 can cap by the standby switch and grounded to the beginning of the ground buss.  Except for the tone stack wires, all signal wires going to pots are shielded.  If you look close, you can see the wiring for the presence control.  The cathode of the 5th stage is connected to pin 1 of the presence pot.  The .1u cap is connected to pin 2 and the other end is connected to pin 3 of the MV.  The presence control is subtle but you can definitly hear it working. 

By this time you should hopefully have a working amp 8)  Why the tape on the back?  I've already mounted the back plate and it scratches easily.  The tape is to protect it until I mount the amp in the cab.