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(LCR also naturally kills tone arm resonance).
It is hard because there are two other tubes on each channel. I also opted for 6c45s made in 1981 with OTK stamps. Not new. I got them for $10 each. They are reflector, but from time gone by. The stage is quieter than any phono stage I have used. I like it a lot better than the high end stages I have used. I tried the Arion, the musical surroundings higher end stage, nova II as well. I even had a vista here. I also tried each of these with hashimoto step ups. No contest. This is as quiet (LCR also naturally kills tone arm resonance). I have had no oscillating from it, though I did put small suppression beads on the grids and made sure I used every pin. No hum unless volume is way up and my ear is on the tweeter. I think that is actually an rca cable issue. It sounds open, airy and full of detail. My friend who has the tango LCR modules (Oliver of the 45 luv thread) is coming Sunday to hear it. I will pass on his impressions.
Those are pretty ugly curves. I have traced on my Utracer and the 6c45 was much better. I have some 416s somewhere. Lighthouse tubes where sockets are unobtainable. I have seen at least one phono preamp built with the 416. I have also been told that used tubes are subject to shorts due to how they were used by bell, but I have no idea. Next project may be a two stage direct heated hybrid stage. CX-340 tubes gyrator loaded with a follower. Maybe 841 instead. Shawn
The DIYer's curves are suspect for sure. Being it is a Bell Lab's tube, I am sure its distortion is quite low. The B version used glass separating the grid from plate and cathode for approx 10,000 hrs life. The C version uses beryllium oxide plus other improvements for double the life since the tube was used extensively in repeater stations etc. I when I tested the tube in College lab, when -1 volt was applied to the grid, the grid shorted to the cathode. The grid "wire" is only 0,0003" dia and only 0,0006" from the cathode. So one must be very very careful using this tube. (I used to have the complete data on the tube.) Here is a photo of the tube for newbies. The grid is the "center ring with threads."CheersSteve
Finally got permission. Here is my schematic (One channel of the preamp). Note I use the 6N6P instead of the 6H30. That required me to reference/bias the 6.3v heater winding to the B+ through a voltage divider. The heater scheme is not on here (just DC 6.3v @ 4.5A because of all the tubes) and the B+ (CLCLC power supply). The unit is dead quiet.Shawn
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