Since the amp is "technically" ready (I could leave on this piece of mdf and just start using it, hoping not to kill myself with all the exposed high voltage wire), it is time to give it its own pretty enclosure and make it into a real amplifier.
this is the enclosure I bought for this amplifier (a monacor UC-152/SW), next to the amplifier that needs to built into it:
I first installed the large components, and quickly made a picture, now that it still looks tidy :-). The panels around the base-plate are just for show. A few days later, they went to a metal workshop to get all the holes punched in them:
A few days later, and it is already starting to look like something. The tube section is completely installed. It is waiting for the panels to return from the metalshop, and then the last pieces can be added.
This is an image I made after I installed the front and back panels that returned from the metal shop. You can see the power and signal connectors on the back, and also the layout of the frontpanel, with the volumepot, the headphone jack and the switch to choose between high and low Z output. This is indeed a different switch than the one in the protype amplifiers. I discovered that the tube doesn't have enough power to drive headphones itself, so the need for a threeway switch has gone.
This is the amplifier 95% done. The attentive viewer would notice the disappearance of the input capacitor on the Szekeres pcb. It suddenly occured to me that I've placed this capacitor there, even though it doesn't appear in my schematic. I've done that, because the cap is in the original Szekeres schematic, and I've made the pcb to that schematic. I have also made the wires from the output capacitor of the tube stage to the inputs of the mosfets as short as possible and also shielded, because these wires were picking up serious hum, transmitted from the 2x12 volt transformer. The hum is now 75% gone, but still present. Some testing later, I found out that the positive regulater of the mosfet powersupply was putting out a 6mV AC ripple, which could be the probable cause of the remaining hum. Too bad that I've destroyed the negative voltage regulator with my testing (shortcircuited the input-adjust pins with a probe...).
So what's left to do:
I don't have any lm337's lying around, so I couldn't repair the amp quickly. I used this pause to make new pcb's for the mosfet powersupply. After all the tweaking, mounting/removing components, soldering/desoldering wires, these two little boards were completely worn out. The powersupply was also still running at 7,5 volts. In the next few days, I will rebuild the mosfet powersupply. I will also mount the mosfet-transformer onto little rubber feet, since it vibrates audibly. I hope that these new boards will remove the last bit of hum, and that I can update this page with images of the finished amplifier and also a description of the sound it puts out!