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In the Forum: Melquiades Amplifier
In the Thread: A different breed of 6C33C amplifier.

Post Subject: 6C33C amp/preamp follow upPosted by KOTriode on: 3/14/2012

The reason that I built the 6C33C preamp was to explore the 6C33C true musical potential like I did with the 845. Not only did I compare the sound of these tubes in power amp, but also in preamp. The reason is that with power amp you might hit some limitation with commercially available output transformer. For 845 there are many excellent choice of output transformer, but it is very limited with the 6C33C. For preamp since the bias current is much lower you can basically use the same preamp output transformer for both tubes, which is what I did. The 845 gives much more bloom in the bass, goes much deeper and give you sense of plenty power, the 6C33C while quite good, has very tight bass but there some sense of dryness (where is the beef?) . But from 100Hz up it is where the 6C33C really shine, the 6C33C can focus on voice and instrument fantastically which I think the low microphonic level of this tube has something to do with it, the 845 imaging is blurred when compared to 6C33C. And then, the 6C33C high is so airy opened and extended, which would make it an excellent tweeter amp. I also think the power is the 6C33C Archille's heel, the linearity of the tubes rank probably at the bottom of your power tube list once you pushed them over 4-5 watts, yes you can corrected with feedback, but then you will loose some of its magic quality, which I dont implement in this amplifier.Now, I have forgot to mention the speaker type used when I raved about the midrange of the 6C33C. I tried them in 3 different system, a Supravox based 8in Field Coil and ribbon tweeter, an Open baffle Supravox field coil bass, midrange and RTR electrostat, and the Stacked Quad. All these systems, even with the 100db sensitivity of the Supravox would need more than 10W to drive, so that eliminates all the flea power amp such as 10Y, 2A3, VT62.... which does not leave much for choice as DHT amplifier. In the future, I would like to try the 6C33C in a horn system, which probably happen in the next 6 months or so, with the compression driver 1-2 watts power required, there will be more player. So, the term "best midrange" so far would apply only to the speakers that I have tried. It is also very interesting that out of 4 different 6C33C tubes that I have tried, they are all sounded very familiar but my preference is the Svetlana labeled tubes so far, they performed as what a good tube should be, no crackling sound, no bias drift, no surprise.... so far.Regarding the "elephant sound", what I meant is that the 6C33C do throw a very large soundstage, depth, a big sound. What the 6C33C did that the 845 does not is the ability to focus on instrument and voices, the image size is just correct, not bloated like the 845, if you happen to compare the 845 side by side with the 6C33C you will feel like you just put on corrective lens with the 6C33C, the image become so sharp, you can hear every little detail but the size of the landscape still is the same as the 845.It is unfortunate that there is not many output transformer choice available out there to explore the 6C33C full potential, it would be nice that there is a transformer available for PSE 6C33C with 40 watts capability, I completely agreed with Paul that any 15 and even 12 inches woofer would appreciate 30-40 watts of power, even the ones with 100db sensitivity. Just for fun, you can see the Stereo 6C33C in action here in action in a tri-amp Supravox field coil + RTR electrostat system along with 845PP and 300BPSE but please dont judge the sound quality of the system through a $100 video camera.
http://www.youtube.com/watch?v=3qvoyh1jznQ

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