SE capacitor coupled Darling amplifier, tribute to Bob Danielak - the creator of the legendary Darling amplifier topology.
Simple schematics, common cathodes, tiny format, budget implementation, easy to build. Pure, non-mechanical sound, affordable for everyone. Requires efficient loudspeakers. Output power is under 1W per channel. Not for loud concerts. But will present quiet music unlike you ever heard, and you will not need to push the volume high when your system can play quietly! (Hint: high power gear suck at playing quietly, that's why it's mandatory to crank the volume with them... )
Parts list (mostly from Mouser electronics, unless otherwise specified):
Power Transformer: Hammond universal 546-369EX PT. 45VA core, 380VCT /75mA, 6.3VCT@2.5A. Faraday cage, low noise winding. 73$
Filament transformer: Hammond 12VCT, 1A: 10$: 546-186C12-BULK
Output Transformer: Edcor https://www.edcorusa.com/xse15-5k
Power supply capacitors, resistor and diode: EPCOS/TDK 180uF/450V for $4 each: 871-B43231B5187M000 (bypass with small DCLink -15uF Kemet).
Power supply filtering: A., RC cheaper option: 270R KOA Speer 2W + UF4007 diode in series. B., Choke filtering option: Hammond 546-154M choke (2H, 100mA, 175DCR), 14$
Cathode bypass for input tubes: 1x.ELNA Silmic II 6V/330uF RFS-6V331MH4#5
Cathode bypass for power tubes:1x ELNA Silmic II 63V/100uF RFS-63V101MI6#5
Coupling capacitor: Easy to source 1uF Kemet DCLink 1.5kV C4AQSLU4100A11J x2 (1.66$ ea) (Try something better if you can! I recommend Obbligato Premium 0.22uF/600VDC, well worth the upgrade cost.)
Input tube plate load: 2x 47K/2W KOA Speer SPR2CT521R473J, 46c each
Volume control: 100K (or 250K) stereo, audio (or log) taper 652-PDB182-K230K104A (few $)
Tube sockets: 2x7pin, 2xoctal (ebay, etc)
Diodes: 3x UF4007 (2 for FW, and 1 for CRC decoupling)
Input tube common cathode resistor: 200R/1W
Power tube (1626) common cathode resistor: 3x150R in series (2W each) KOA Speer 660-SPR2CT521R151J (1.5$ total)
Power tube grid leak resistor: 2x 220K/1/2W KOA Speer grid R for 1626
Grid stoppers for all tubes: 4x 200R 1/2W KOA Speer
Highly recommended upgrades: middle Edcor (7.6K) or even better Edcor CXSE series OPT. Use choke for input, and Obbligato for coupling capacitor.
Notes on output transformer:
Bob Danielak specifies 5-7K load. I would recommend a 7-8K load for purest sound. 5K load will give more grunt, more "power". So, choose purity (7-8K) or power (5K). Or anything in between, that you can find or maybe already have in your spares box.
Output transformer choices, from bargain basement to highest end:
https://www.edcorusa.com/xse15-5k (cheapest)
Hammond 125ESE: cheap & versatile
https://www.edcorusa.com/xse25-76k (much better)
https://www.edcorusa.com/cxse25-5k-2 (budget kick-ass)
http://www.tube-amps.net/Hashimoto_Products.htm (H20-7U, king of tone & freq range - superb but $$$. If you go for this high-end OPT, then I recommend to build the Pure Darling version so the rest also matches that level.)
Alternatively, you can try vintage stuff from ebay: Sony/Telefunken/etc RTR OPT. Any vintage single ended iron (NOT push pull!) that has a primary impedance from 5K-10K. Choose secondary to match you spreakers. Although I recommend 8R secondary as a minimum. Using speakers lower than 8R impedance severely cripples this amplifier. It's like giving lead boots to a dancer and expecting him to dance.... you need dance shoes, which are 16R. 8R speakers are like outside shoes. Can already move around with them, but it's not graceful yet.