Allright, now that all the design stuff is done, let's go on with the construction of the amplifier.
Here is an image of the powersupply in action:
The powersupply gives a nice +/-10.35 volts (a 9.1 volt zenerdiode is used and the regulators themselves add another 1.25 volts). The image is of the first powersupply. Because of repetitive tweaking and testing, the pcb's were worn out, so I've etched a new set. They're exactly the same.
And an image of one Szekeres PCB:
The protection diode is removed from this board, for some troubleshooting. I reinstalled it later, when I found the problem. Also, this is with the first resistor. Allthough this is a 5 watt resistor and this resistor had to dissipate only about two watts, it got extremely hot. In the final amp, I've replaced these with 25watt resistors, with a nice and shiny gold-colored heatsink. They don't get nearly as hot.
I finally had obtained all the parts necessary to build the amplifier. When I saw them all packed together in a box, I got a little itch to get an idea what the amp would like and also to get an idea of all the work that needed to be done. So I layed out all the components and took a picture
This is an image of the first prototype amplifier. And with some pride I can say: It works!! There are some issues to be resolved, but that's why it's mounted on a board of MDF, with all components readily accessible.
This is the second prototype. The 5watt resistors with heatsink on the back are replaced by the 25watt versions, the 24VA transformer has been replaced by the 48VA one, an ALPS volumepot has been installed and there is an hum pot on the heater of the tube, to get rid of the hum that was present. This one has been measured with a spectrum analyser (thanks Remco!) and it has a S/N ratio of about 70dB and can play fairly loud before showing a 1% distortion. But not loud enough, so I've decided to crank up the mosfet powersupply a little, going from 7.5 volts to 10 volts.
Well, it seems that it works, so all that is left to do is put all this stuff in a nice enclosure. Which you can read about on the next page.