I am building myself up to doing my first tube project using Lorcan's layouts and pcbs from here:
http://lorcan.me/bass_preamp (http://lorcan.me/bass_preamp)
There is a photo near the bottom of the page of his build. What is the box that sits between the power socket, on/off switch and power supply on the left of the photo? Is this an optional extra? I couldn't see any reference to it in the layouts.
The silver box is an RFI filter, you can see the schematic on the top of the box, two caps (X type ?) across the power lines and two inductors in series with the two power lines. I would consider it optional, when i do put one in i use discrete components.
Many thanks!
I have etched the boards and I am now fretting over the type of capacitor to use for the tone stack, 2 100nf and 1 47nf capacitors. I have got polyester caps for the right voltage which should be OK but when I look at the pictures of Lorcan's build and of the original Alembic build I can see these much bigger caps. I got radials and had to bend out the legs so that they will fit. Will it make any real difference which type I use? I am guessing the originals are Orange Drops.
I have already googled and come across different opinions.
I gave in to myself again and ordered Orange Drop capacitors. I just couldn't leave it alone.
OK, I have just about got it finished. I hit a bump when the transformer I bought turned out to be faulty, a shorted turn I think. It got really hot and only put out around 170 volts dc after rectification. To be fair to the supplier, he has sent me a replacement.
Just one last check. Again using the schematics at http://lorcan.me/bass_preamp (http://lorcan.me/bass_preamp), on the power supply board in the heater supply section there is a 68 Ohm resistor connected to the led. Is this purely a current limiting resistor for the LED? I used a 1K resistor because the resistor value seemed really low. Does this matter?