I remember a couple of years ago we did a thread like this, where a few folks shared their individual bias mods. I thought it was pretty cool and got a few ideas on building them. It seems there's an interest in making them so I thought I'd share my IBAM building method. There's a lot of ways to do these, but this works for me. I use the IBAM more b/c I like old stock 7868/7591s and find at times with the IBBA I have a hard time balancing a pair. If I get new production tubes then I'll use a IBBA - I think it's the better board as there's a fail-safe feature that protects the unit when there's a run-away tube. At least that's how I understand it. But, TBH I've been using the IBAM for around 6 yrs and never had a problem with one. First, you'll need the parts: 4 x 12k resistors 1/4-1/2w, 4 - 33uF/50v e-caps (anything close will work), 4 - 10k 1/4-1/2w trimmers (I like multi-turns, but singles are good too). Some solid core hook-up wire and a perf board. I mount the trimmers first and bend the leads as shown in the pic. One side of the trimmer on all four are connected to a buss that feeds the filament voltage to the preamp tubes. I use a yellow wire as that's usually the color that Fisher used on 400s to run that supply. After soldering the trimmer leads to the buss mount the 12k resistors. Mount them so one lead of the resistor is touching the other side of the trimmer - not the middle or wiper lead. Solder these. Now, mount the e-caps where the negative side touches the wiper lead on the trimmers. Bend the two leads at each junction like a teepee, your going to connect the lead that goes to each of grid resistors - 330k or 220k. I like to bend the end on these wires so you can stick a bit in the hole on the perf bd then bend the leads - the teepee - on the caps and trimmer wiper where there's a good connection, then solder them. I use a different color wire for each of these but it really doesn't matter. The alignment of the trimmers on the board are the same as the output tubes, i.e. the top trimmer works the top output tube, and so on. That's with the unit standing upright resting on the power transformer. So make sure that the wiper wires to the grid resistors go in the same order. You want to adjust the trimmer while your reading the voltage on pin 3 for a 7868. The last thing is to run your ground buss so that all the remaining leads: the other side of the 12k resistors and the positives of the caps are connected. I hope that wasn't too confusing but now your board is done. Testing: check resistance from each lead to the grid resistors, to ground and to the supply to the preamps. That's 8 checks. Adust the trimmers to make sure the resistance changes. Mounting the board: I like to mount mine on top of the new e-cans (1000uF) to the bias supply. I remove the clip and shoe-goo these cans to the chassis. The board gets an insulated backing that's tied to the board with plastic zip ties. Then the board is shoe-gooed. I use a 4 way terminal for the grid resistor leads. If you need to get to the board later, hopefully that won't happen, but just cut the plastic zips and you can mess with the bottom of the board. I'm sure there's better ways to this but this has worked for me. I liked to see how others do their IBAM/IBBAs, we can all learn from each other.