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OK, it took for a while but at this point I have nailed down all design aspects of the new 6-channels Super Milq, and particularly its input stage. I have listen and evaluated all solutions that will be implemented in there; selected, appraised and ordered all ingredients and now I am at a straight finish line with this amp. At this point I know how it will be finished, organized on context of my acoustic system and how it will sound when it will be done.

Here is the semi-final diagram of the 6-channels Super Milq input stage. I said “semi-final” because the values or 2 “red” resistors in the C and F channels will be slightly changed later on, but it will be very minor and will be no more then 20% from where it now. I will make the adjustments on that this image as it is the only drawing that I have and use for the assembly.

A few words about the Super Milq’s final solution.

Lower bass “A” channel: There is no change from what 3-channel. The Super Milq was the same: first order at 65Hz, two stages and 53W dissipation on 6C33C plate at 200V. The coupling cap I dropped to 4uF, did not go for electrolytic and still stay with film cap. I have deseeded do not do inductor as the filter and to say with RC chain. If I found 15H-30H indictor with VERY low DCR (20R-50R) and relatively small dimensions then I might go for it. So far the only inductor that I accept in there sonically was 11” tall and had weight of 25 pounds - I can not fit it in there.

Midbass “B” channel: Everything is straight forward in there.

The Injection “C” channel: The 30K 24-steps L-pad with RN60 resistors and Alma switch is nicely transparent. I do not high-pass this channel at line-level and as a result I have nice full-range Milq amp built-in with which I might drive anything I wish- very convent and I do not need to keep a separate full range Milq around to play other speaker’s drivers that I get from time to time. I can even to connect the second filament on the 6C33C and use more power from the channel. (The OPT has 250mA gap.) I found it very good to have this channel built-in nit to mention that it does very goods job to drive the Reds of the Injection channel. Perhaps now I might let my full-range stand alone Milq to go….

The Fundamentals “D” channel: The first singles stage channel. I use 5E6P in there. To mess-up two closed operating line-level filters was not good idea. Since the channel is low passed I did not detect any negative influence of the caps on the secondary. The channel has also attenuation at speaker level and is used ~ 6db below the MF channel.

The Mid Range “E” channel: This is a purely a shine of the whole project. I use 6E6P-DR as a driver  and  RL filter. Absolutely nothing in capacitive world (mica, teflon, polypropylene, polystyrene) was able to give me the result I got from the RL filter.  Air cap was the best among caps but RL filter was superior to air caps. It does apparently serves the purpose does not put anything in series… So, the RULE is: no capacitors in high-pass if top is wide-open. I shell write more about the selection of the filter for MF in future as it was very interesting journey.  It was exciting to learn that D, E and F channels do not need as lot current as I initially thought and I use 30mA at 200V, which dissipate moderate 6W on plate. The coke I use is Hammond 622ZA in a Co-Netick can. I have also another “alternative” very interesting output transformer for this channel to try….

The HF Range “F” channel: The 6E6P-DR at 30mA connected at tetrode. The filter is second order with Sowter 9858 Pultec MEQ-5 EQ Inductor 420/277/145/108/61/34 mH) and variable air cap. The variable inductance and capacitance allow me to write any prefer Bessel curve against any frequency I wish and I have now much more gain on in tweeter then I need. The driver is tetrode strapped to defeat the insertion loss of the 175:1 transformer and to have more then necessary gain to run the “Water Drop” Tweeter on transition slope, crossed at 30kHz-40kHz with second order. The shortcomings of the tetrodes (loosing of damping, increase of output impedance and so on…) are absolutely not applicable in my case as the ribbon tweeter care less about the damping. In fact if I have a tube with more transconductance then 6E5P-6E6P (30-35ma/V or 30.000mS in Western scale) that has >3-4W on plate and more then 2-3V of bias I would stick it in. I might use something like 7788 pentode only with more power and more bias. If you know any of them then please pitch it to me as to have too much gain on tweeter do not hurt. Do not forget that the chennal will not do “sound” but rather the “space noise”. Still, even what I have now is ~ 12dB more then I need and it is already is very good.

In the end: the layout of the things is really perfect and I do like very much how it fits. I practically (air cap is an exception) do not use any extra wire at all for signals and bias – just the natural leads of the parts. The bias attenuators, after much evaluations, I ended up to use Bourns 83 series that are a perfect balance between the geometry, wirewound multi-turn precision/reliability and sound quality.

http://www.bourns.com/pdfs/8384.pdf

It is pretty much it and not I need to render it in the final implementation….

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