About two weeks ago I thought I had finished it only to find that only one of the six sections worked as it should! I wondered if my use of screened cables had caused extra capacitance and some unwanted feedback.
Actually, I had made some silly mistakes in the wiring. Two components were wired to tags that were bolted to the chassis so a signal dead short! It was so crowded in there that I had failed to see the bolts! Other problems were simple switch mis-wires.
One by one I got all the six sections working and in the process I found it to be a very elegant design. The use of cathode followers ensures that the gain is never more than one, so the feedback is very stable. 12dB/octave through one CF or 24dB/octave through two!
I will post some final pics before it's shipped next week. I will also show where there are a couple of mistakes on the official schematics.
There were so many tubes, I had to label them inside and out to keep track of it all.
It looks overwhelming but it can be done by very carefully marking your progress on a build copy of the schematic.
I had to drill extra ventilation holes for the power supply, there were more on the base cover to get some convection currents going.
The blue presets are used to set the outputs of the six sections according to the original schematics.
The supply voltages I used were 280V for the ECC83 tubes, 260V for the output E83F and plus and minus 100V for the cathode followers. I prefer to use 6DT8's which are a more robust 6V version of ECC81's. The maximum voltage for a half watt resistor with this current would be 139V, so I preferred to stick to plus and minus 100V. There is no info on voltages in the manual, so I had to work them out for myself.
This shows the front panel lit up, I hope Ian manages to make sense of it all!
Thanks to everyone for your support on the project, it has been the most challenging I have ever done, especially with the domestic situation in chaos at the beginning.
I don't really count the hours as it's my hobby, I had to redraw all the schematics first with rotary/toggle switches, so about a month or so. Then I had to plan the front panel to see if they would fit, several weeks. Then planning the amp layout, again several weeks. Building the chassis was the easiest part and then fitting all the components., two months. The labeling of all the switches took several weeks printing etc. Wiring up all the switches about a month, then fault finding took several weeks.
The most stressful part is that you can't make a mistake, as it's a one-off and represents a lot of money and effort. Like building a house of cards that only becomes strong when the last card is in place.
It arrived here and this UE 100 sounds and looks fantastic.
I’d not ever been near a real UE 100 , id only read online that it was a fantastic EQ.
And it hasn’t disappointed !
The tone of the box is gorgeous. And the EQ, especially the high end , is smooth and airy.
Very different sounding indeed to other EQs I have here — a pultec (built by Dave) or the vintage alteq EQ....
I’ve just about mastered the buttons now.
And today I’ve been happily recording vocals for two tracks for an artist (Hannah Grace) album today and it enhanced her vocal & acoustic guitar overdubs greatly.