First tests

With all the parts finally in place, I could wire things up. My chassis is snug, but not unworkable in terms of space. It's tricky to get the input audio connected right next to the chassis wall. The picture at right is still with most of the wires loose. I twisted them where possible and wired it up first for basic triode mode without cathode feedback or supplemental capacitor.

Grounding is still a bit mysterious to me, but after reading some online posts, I think I get the concept... I have only one place on the PCB that goes to ground (through one of the input connectors) and then all the metal things around the chasssis (top, back and front panels, transformer bolts, choke frame) get grounded to a star ground point that goes to the earth ground on the power plug. I didn't quite grasp a few things but think I finally understand that the speaker terminals without cathode feedback need to ground not direct to the star ground (chassis) but back to the PCB to avoid ground loops that may create hum.

I first set things up with my old Infinity speakers that I refurbished (see a few posts back). I connected it all up with a cheap CD player with a simple headphone plug, plugged in a fuse, and turned it on from a power strip across the room... a few moments later the tubes warmed up, a nice little glow, and... music! It worked and sounded pretty good!




Glowing nicely with the lights out!

Once again, I don't know much about electronics, but I read a few things about measuring voltage so I tested the B+ and saw it rising 100, 200, 450, 700, 1000+ uh oh! That sounds way too high! Then I realized I had my multimeter set to AC and once I finally got things sorted out I see it hovering in the 469-479 range, sounds better. I also tested the cathode voltage on one of the output tubes and with a few calculations I estimate about 55 mA per tube and roughly 24 watts, seeming to match what might be expected. If I was smarter about this stuff, I'd do more measuring, and some of my next steps are to understand the circuit better to really grasp what's going on.

 

The CD player was not very good, so I switched over to use my iPhone (I know, probably still not the best quality) and that bumped up the quality a bit. I also tested wiring the amp using cathode feedback, which didn't sound dramatically different to me. I haven't tried ultralinear mode, but may test that later. I then moved the amp to my living room and connected my bigger and better quality Klipsch speakers (F1s, not great, but pretty efficient and better bass) and my laptop with MOG (now Beats) for pretty good quality digital streaming. So far so good!