I have two preamps in my collection earlier (well there was a third). Think my SRPP line stage copied from Elektor Electronics is not functioning all rigt. The Octal 6 (from Mapletree Audio Design), which actually is an Octal 4 as I only use the version with a 6J5 + 6R7, is working OK. The third was a mysterious thing from Russia (AML+).
The reason for this project was the two inductive potentiometers I had gotten from a friend in Malaysia, a great amount of tubes a chassis and some transformers suitable for preamplifiers.
I picked the Blue Velvet of no particular reason, maybe becasue it was so un-kinky. The schematic is copied from Dick Olsher and Kara Chaffee (See their website), though the graphic is rather hard to read, so I redraw the schematic. The ECL85/6F5P is an add-on that will be installed (maybe) later on. It's a simple regulator, but until then I will feed the amp from a 240V-transformer, rectified through a diodbridge (4 x 1N4007) and filtered by a CRC-filter (100uF + 1,1kohm + 100uF).
I will use a pair of 6N8S (Russian equivalent to 6SN7) and else very standardized components. Resistors are metalfilm (1% 0,6W) and capacitors are polypropylene (RIFA) and polystyrene (no-name) , as I had those at home. Else it isn't shown anywhere that special kinds of capacitors are "better" than not special kinds. It is even so that many manufacturers randomly pick standard caps, marks them with some HighEnd-label and sets the price tag 10 times higher.
Cables are also "what I found in my drawers". Switches are cheap ones from Conrad's Swedish web shop. Transformer is a standar one from Mike in UK. RCA connectors are great stuff from VT4C in HongKong. Chassis is a vintage froma tube amp kit (Swedish?), and so are knobs, main switch and neon lamp holder.
Shortly this is an easy and financially reasonable project.
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