Step 12(B) - Main Board Installation

Billy Batz · Post by **Billy Batz** » Mon Apr 28, 2008 8:57 pm

Im working on this step today when I can but when done the amp is basically finished.

I prefer to populate the board prior to installing the board into the chassis. Its just easier to manipulate the compoannets on and around the board and solder things when its out. I also solder enough wire to each turret to reach where it will go once installed.

Building the board and installing it are both probably the most time consuming parts of the build. Its a pain to rout wires around under and between and around the boards, through the perf holes, and trim, strip and soldering each of the many wires.

Billy Batz · Post by **Billy Batz** » Tue Apr 29, 2008 11:35 am

Most of the wires on the tube socket side and the pot side, I leave a few inches more then I need so I have room to route/trim the wire. The connections to the jacks pots and tube sockets are exactly the same as the 100W kit instructions. There are a few differences in the bias and power connections Ill describe.

There's basically ony 2 spots I leave unsoldered in anticipation of wires from the OT and choke.
- The first is the turret (circled in red) on the very corner of the board where the bias diode is. That corner turret is used as a junction point for the choke, OT CT, and a red wire from the main filter (circled in purple ont he power board). They all have to be soldered as you install the board (dont actually bolt the bard on until your finished.
- The second is the turret (circled in yellow) on pot side of the board next to the bias resistor attached to the 8.2k decoupling resistor. That turret gets a junction of the other choke wire as well as 2 yellow wires- one will lead to the output tube socket pin 6's, an the other to the screens filter on the power board- the 2 series 30u filters on the preamp side of the rectifier diodes.

Most of the wires are simply trimed, striped and soldered to their jack/pot/socket except for a few that get routed to the power board. The corner turret on the pot & PT side of the board (circled in white) goes to the turret where the nearest diode connects to the PT HT secondaries (circled on the power board in white).

The turret on the mian board circled in yellow goes to the output tube socket pin6's as I said but also to the power board turret circled in yellow. Its the screens grid filters positive terminal left unsoldered awaiting this connection.

The turret on the other side of that 8.2k resistor (circled in orange) has attached to it a yellow wire that goes to the power board V3 filter which is the single 30u cap whose positive terminal is was left unsoldered again awaiting this connection.

All these connections I route together in a bundle that I wrap with zip-ties or that lacing if thats what you like to do to keep it neat.

gutpile · Post by **gutpile** » Thu May 01, 2008 11:35 pm

I populated my board tonight (no soldering yet) here are some pics... Don't forget to take some steel wool or sand paper to the NOS AB resistors as they will have a film over them... Also, go around the hole for 15K resistor on the far right side of the board... you will need to put a mounting board screw through it so don't cover it up or you have to do it again.... I still have to add the bias adjuster... I'll have to take everything off to do the wiring but my wife wanted me upstairs to watch Lost with her and this is the only thing that she will allow me to do upstairs...

Hey BB is the 180K resistor on the very far right side OK? (brown-grey-yellow) Your layout has a 150K in that spot...

Billy Batz · Post by **Billy Batz** » Sun May 04, 2008 5:04 pm

I guess whatever gets the bias in range.

I will get to this last part of the build eventually I swear.

gutpile · Post by **gutpile** » Mon May 05, 2008 11:38 pm

here is my board soldered less the bias adjuster...

shakti · Post by **shakti** » Tue Jul 01, 2008 5:16 pm

My AB kit didn't come with either a 150k or 180k for the far right resistor. The only spare one in that range is a 220k. How will that work?

Billy Batz · Post by **Billy Batz** » Tue Jul 01, 2008 6:38 pm

shakti wrote:My AB kit didn't come with either a 150k or 180k for the far right resistor. The only spare one in that range is a 220k. How will that work?

Your bias will be way too hot. Just use a CC or order a 150k from here if Metro doesnt have one:
http://www.tubedepot.com/resistors.html