Wiring the circuit board

I started attaching the wires that run from the circuit board to elsewhere in the amp. There are ongoing debates about the best wire to use for different situations. For example, some wires carry high voltage DC to the tubes' anodes (plates) while other wires carry low voltage AC signal to the tubes' grids, and one can understand how the type of wire could ultimately make some timbral difference. Some folks say they can actually hear the differences among wires of varying gauge, composition and construction (stranded vs. solid), and others say they can't. Some say selection choice is more about ease of laying the wires and making good quality connections, or whatever Leo or Jim's engineers decided back in the 50's and 60's. Having no real interest in historical accuracy nor any useful experience doing this, I lean toward the "ease of use" approach (lighter gauge solid wire), thinking I'll probably just do a better job overall since it's easier to put things just where I want... but in other projects I've done (from carpentry to coding) this approach has often worked against me in the end, coming also with limitations in durability or flexibility. So, I go with Michael's recommendation and use silver stranded #18 definitely for the strictly-signal wires and also for as much of the others as I can. I have a lot wire to choose from, but I don't think I have quite enough to be consistent throughout. so I'm using other #18 stranded, as well as some #20 solid in cases where I have multiple wires connecting on one terminal and need to conserve space. And, my predisposition to conserve and repurpose materials means I'll also use up scrap wire bits trimmed from the transformer (which are so pretty!). So, it's a hodgepodge with an aim to place the highest quality wire where it probably matters most, and my whims, within generally acceptable bounds, for the rest.

I use the scale drawing of the chassis floor to measure the length of each wire lead before soldering it on. Grey #18 stranded for the plates and cathodes, black mostly stranded some solid for grounds, red stranded mostly #18 some #20 for DC supply, white/blue #18 stranded for the signal wire)

(Circuit board with about half the wires in place.) 

I've completed the front panel controls as much as possible prior to making the connections with the board and mounted everything, though some front panel pots remain only lightly attached since they'll have to be pulled back to access the front terminals when I make the final connections to the board. Throughout the process of adding components, I was doing testing to make sure my switch and pot connections were good, and at one point got unexpected results. The connections were good, but I realized I had soldered the wrong value resistors into place from the jack (tip connector) to ground - should be 1M ohm, and I had 100 ohm resistors in there for some reason. I suppose it's partly because I haven't fully sorted and binned the gajillion resistors that got mixed up in transit, and some of them ended up in the wrong drawers. But mostly, it's because I have never bothered to learn how to interpret the resistor codes printed right on them (just laziness on my part).  So I test them before placement to confirm the values, but must have forgotten to do that in this case. So, I pulled the jacks once more, and put in the right resistors. 

(The mostly-completed front panel controls. (Left to right) presence (high cut), master volume, mid, bass, tone stack select switch, treble, normal channel gain, lead channel gain, (bottom 3 in a row) gain boost/cut switch, V1a cathode resistor select switch, normal channel impedance Hi/Lo switch, (above the three just noted) channel mode select switch, lead and normal input jacks.)

On the rear panel, I had trouble making a good solder joint with with the output transformer leads to the speaker jacks, the solder just kept balling up and looking wrong. Turns out, these leads, since they come directly from and are probably literally a continuation of the secondary winding, are coated with the same thin insulation material (think thin coat of polyurethane) that keeps the wires of the winding coil from shorting each other. Since I clipped these leads down in length, I clipped off the ends that were left as clean uninsulated wire, so I as was trying to solder insulated wire. I discovered that one must burn off the insulation using molten solder in order to clean the wire. Immersing the wire end in a glob of hot solder for 15 or 20 seconds seemed to do the trick. Normally I'd be able to put my ohmmeter on each end of the two wires soldered to the joint to test continuity, but in this case, the end of the transformer wire is buried somewhere inside the transformer, and I just haven't taken it apart to test it yet, so we'll see.

 

(rear panel connections complete: (left to right) speaker outputs, negative feedback selector switch, power tube bias test points,  rectifier select switch)

I've also updated my layout (below) to better reflect actual placement of things... updating actual wire colors will be the last thing I do since that' s a work in progress. 

You may notice there are some new resistors on the pots that are not shown on the schematic (which I'll update one of these days) - this is due to my not having the right value pots in some cases, and really wanting to use what I've got. The presence pot is 25k ohms (should be 5k), the TMB side of the treble pot is 500k ohms (should be 250k) and the TMB side of the mid pot is 250k ohms (should be 25k). It's mainly that I'm thrifty - I just can't see spending $10 - $20 on special duplex pots that have two different values on one spindle, as my dual tone stacks require. And in the case of the presence control, I've already got a PEC 25k pot (military grade high quality) so why not use it instead of doling out another $4 + shipping?  The extra resistors work in parallel with the pot resistances to make them function as if they were the spec'd values, so the electrons moving through the controls "feel" as if they're experiencing what's shown in the schematic. 

... And, here's the fully wired board. 

I still need to clean up the flux and solder splatter and and go over all the connections to be sure they're sound. Next will be going over the final schematic to be sure it's right, and final layout once more to be sure layout matches schematic matches what I've done to date, before I shoe-horn the board into the chassis, install components, and complete all the connections.