Here is the general specification for the parts that I used. The selection of the parts implies some liberty of course. It will be your amp after all, not mine - do whatever you wish. In some case when I feel that requirement is critical I will stress it. Please do not accept my words as recommendations of some kind if DIY specialist – I’m not and I have in fact very rudimental experience in the subject. So, use you own common sense and your ears – it was what I used. Do not forget that Milq is not the amp that would need any extravagant parts – you just do not need to use bad parts and all the rest will be taken care by the sound of the topology. Currently there is two known to me built Milq– Dima juts finished his amp but has no OPT yet and a guy in Sweden I believe (he never passed at my site). I hope they both show up here and update about third experience or perhaps recommendations…
Power Transformers. My own version Milqiades uses input choke filters everywhere but it is not what is necessary. The First Stage and the Bias Supplies do not need to have choke input. If you go for CRC, CLRC filtration or for tube rectifications then recalculate currents and voltages of your transformers accordingly. The voltage and currants in my specific case are marked at the circuit: (TR1, TR2 and TR3). I do see a rational to separate the filament and first stage transformer but it is not mandatory. Whatever you do make the TR3 transformer to have as low impedance as you can. The Output stage must use SS rectification and input choke filter.
Output Transformer. This is the key element and if you have the transformer then the rest of the amp so very easy. An Amorphous core is absolutely mandatory. Make it to be able to care 250-350mA, depends the core size you will be able to find and how hard you will be wiling to drive your loudspeakers. The 200mA at 200V is already acceptable operation mode for 6C33C, particularly you have high compliance/efficiency loudspeakers. However, you might go up from there until you get 50W-55W on the 6C33C’s plate. With better speakers it is unnecessary thought. Keep the DC gap in your transformer large enough for at least 15% of reserved current (if you will be driving through the OTP 250mA then use 280mA gap) Your OPT will be from ~ 6:1 to 11:1. I intestinally do not give is the precise specification for transformers because it is “depends”. If I build it now then I would go for the re-mappable configuration of 8 or more secondarys, 8:1 in the middle mapping, DCR primary <50R, 320-350mA, inductions enough to give 17Hz-18Hz at 20W. Prepare to pay around $1000 an Amorphous transformer.
Diode Bridges – I used full valve bridge rectifiers if you wish to go for other topologies then redo the secondary’s of transformers accordingly. Use the ultra-fast and soft switching diodes. Schottky are highly advisable
but watch for the size of your capacitors. The Schottkys of that voltage can care <7A. The choke and the between-filter-resistors are a very good buffer for transient current but it is depends how ridicules you will go in the last capacitor values…. In the worst case you might put an extra soft start in the B+ of output stage.
DL1, DL2 – any time delay relays you like and was tested by you for sonic transparency. I used Magnecraft series relays. Also, you might use other delay schemas, not necessarily the off the shelf relays - it is up to you. I went for the Magnecraft series relays because it is ready to go and had no sonic problems that I was able to hear – I decided to do not reinvent the bicycle….
L1, L2, L3, L4 – the regular Hammonds do juts fine – they have low DCR and very nice made to be silent while handling the input choke ripples. The L2 should be particularly silent as it will care a lot of current with very high ripples. It should be well varnished and well baked. I used Hammond 193Q Epoxy “Ripley" version that is a regular choke double dipped in epoxy – before and after the final assembly. If you have money then I would go for a caned toroidal L2 – it will be even more silent. We are talking about a purely mechanical noise…
The V1/V2 tubes are 0A2 might be substituted with SG1P,STV150/30, StR150/30, 150C1, G150m 150C2, 150C4, CV10664, CV1832, CV2903, CV8161, HD51, M8223, QS1207, GD150/4K, QS1210, SR56. Use any brand you wish.
V3 is 6E5P might be substituted with 6E6P or 6E6P-DR, no 6E5P-E or 6E6P-E must be used
V4 is 6C33C, 6C33C-B or 6C18C, any brand and any vintage.
All electrolytic capacitors I used Nichicons LK, VZ, NR, NX. Use whatever you wish, besides Black Gates. You might keep the “last caps” C2, C8 and C9 as C10 as it market or you can go for higher values. The Super Melquiades has 6.000uF of C2, 2000 of R13. 13.000 uF of R14 (that is negate bias - very critical) and 45.000uF of C10. If you can make more absurd that I did then you will winn a nomination of being more certifiable then I am but it will not make your amp to sound better. Read the section about the Diode Bridges again.
C3 is Electovube 950B or 950D. You might use any best 400V cap you know of - it is a very critical cap. Keep it = 2uF or above
All low wattage resistors (with non-marked power) are Dale RN60 (CMF)
The R2 is 12W Mills weirwound non-inductive.
The R22 is 30W-50W Vishay/Dale weirwound non-inductive.
R11, R12, R17, R15, R16 I used Mills or Vishay/Dale’s CW, RW wirewound.
VR1, VR2, VR3 - any high quality, precision >5-turns trimmers. With the the VR2 I would go wirewound and the rest whatever you wish, with bulk metal-foil being my preference.
The tube sockets for small tubes - Connex Tube Sockets, for 6C33C - any you will find. There are expansive Johnson and Japanese Teflon– they are more the subject usability then sonic results.
Cables - absolutely nothing special. No silver, no high-tech stuff - a regular common reasonable-gauge hook up wires. Use >14ga for 6C33C filaments. It is preferable do not use any wires for signal path but use the natural parts leads – however it will be upon your layout. Use 6ga automobile grounding stranded cable for mains negative buss terminal of your amp.
Soldering – no high cont silver solder. The Wonder Solder as the similar with low silver content are fine.
Meters – you might use milivoltmeter or miliampermiter, once again it is upon your layout.
It is very important to visualize and eventually after you get the parts to plan,l the layout of the amplifier. The Milq circuit is drawing in the way that gives a very clean idea how it might be. Here some basic tips:
1) Keep point “M” as close to R2 as possible.
2) Keep point “L” as close to R18 as possible.
3) Keep C10 as close to OTP as possible.
4) Keep R4 and R6 as close to grid as possible.
5) Keep R5 close to grid as possible.
6) Bring the C4 and C5 ground leads right to the gas tubes sockets.
7) Keep the gas tube very close to the first stage’s grid
8) Keep filament supplies far for the signal paths
9) Keep OPT as close as possible to the V4
10) Keep V3 and V4 as close as possible.
11) Keep V4 with an island where no parts will be closer to the tube socket then a reasonable temperature permitted distance.
I do not advise anyone about the chassis – it is purely your chose. If you do no go for moonoblocks but for a stereo amps then you might integrate some power supplies. It would require some recalculations of transformers secondarys.
Planning step is very important. Get the largest parts, make a cardboard box or 1:1 plan and try to position the elements inn a way you like and in a way that will maximum benefit the currents flows. It is always a good idea to keep PS off the main amp chassis. If you go for it then pay double attention to the quality of the cable and connectors between power supplies and the amplifiers. If you go for a separate power supplies then keep the “last” caps of the PS chain on the amplifier chassis, niot on the PS chassis.
I do not spend a lot of time talking about planning - it is your job. If you do it well then your following success will logically flow from a good planning. Rgs, Romy the Cat
"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche