Preamp Deal of the Century

I've learnt a lot from this thread, and certainly appreciate the sharing of info re the 6F6. For what it's worth, I did ask Mick about this about a week ago. He simply said "No;" he would not recommend it. He did not elaborate. Mick's take is of course valuable, but it is not necessarily a trump card, and Ecclectique your experiences with it are a great contribution to this thread. Thank you.

Re the Ken-Rad VT-231 black glass, they made an immediate and noticeable improvement in my system (tube CDP, Chardonnay, SS amp, Hales speakers: a greater tube "bloom" and deeper bass; no unreasonable microphonics). Clearly, system dependency cannot be ignored.

Is the 6N23EV a drop-in replacement for the 6BQ7?

Just picked up a Music Reference RM-200 to amp a Chardonnay, using a half-recipe of Chris VH Cat-5 to drive Hales Revelation 2s. The RM-200 has 8, 4, 2, and 1 Ohm taps, with a hybrid design that allows the lower taps to produce successively *more* power (contrary to most amps) and rely increasing heavily on the pre's amplification; i.e., using a lower tap shifts the total (amp + pre amp) amplification more towards the pre, requiring less from the amp's KT-88s. In the Chardonnay I'm using a 1955 Mullard CV 378 (GZ-37) rectifier, 1940's era Sylvania 6L6GA regulators, and 1940's era Ken-Rad Black Glass VT-231 line tubes.

With a tube CDP source, high end extension is very good, with sweet harmonics, a delicate, long decay on bells, and a "splash" on cymbals; mid-range has a true tube bloom, but not too much; mid-bass is tight and crisp, and bass, while perhaps not the absolute end-all in SS composure, is still quite good and low and strong enough to be felt through my feet when sitting six feet away with no sub-woofer. All this collapses if the source is not well mastered (more the rule than the exception) or if the volume is at a background listening level (sound is then very good, but--presumably in part due to the Fletcher-Munson effect--not at its best). I think improvements can be made in depth and soundstage, but I'll look at the room and isolation tweaks to try to capture that.

All-in-all, a nice synergy with the Supratek.

Thanks Ecclectique. You're probably aware that Roger Modjeski uses the 6BQ7 as the driver for the Music Reference RM-200, and he has been quoted as saying that you can drop in a 6922 as a sub in that application. I want to preserve the finesse of the Supratek down the chain, so I'm looking for NOS in that driver position. I'm all too aware that substitutions are not necessarily transitive (i.e., sub a 6N23EV for 6922 and a 6922 for a 6BQ7 doesn't necessarily imply subing a 6N23EV for a 6BQ7, but ... ).

P.S. Finally got around to dropping in 6F6G's in place of the 1940's Sylvania 6L6GA's as regulators in the Supratek. It's too early to site differences, but certainly an excellent tube in that position.

Hi Ecclectique--most interesting. Sometimes it seems like half of high fidelity audio can be attributed to half a dozen extremely impressive individuals. I was cued into the 6922/6BQ7 sub in Roger Modjeski's "Manufacturer's Comment" to the 2002 Stereophile review (http://www.stereophile.com/amplificationreviews/560/index8.html). The relevant context is this excerpt:

Through my research, I determined that the much-maligned Chinese 6550 was capable of the highest peak-cathode currents of any 6550 available, and about 1.5 times higher than the venerated Genelex KT88. Once the grid-leakage problem was solved through the driver design, it was full speed ahead with the Chinese tubes. Granted, I have to toss quite a few, but far fewer now that my driver circuit can tolerate grid leakage. As to rolling the driver tube, if you like the 6922 or its higher-current 6H30 version, go ahead, the circuit won't mind—though in this application I prefer the 6BQ7 for its ruggedness, less delicate grid, and higher current. Just be sure the DC is matched in the two sections, as it is directly coupled to the output grids. We want to keep the bias balance within 10% in the output tubes.

I take good note that a 6922/6BQ7 is *not* a general substitution.

There is something a little more interesting going on here. Pre-amps like the Supratek that use 6SN7s and 6L6s are fertile platforms to rolling; there is no question that NOS tubes elevate the performance. But the KT88 is a desert for rolling; there is the GEC/Genelex and Tung Sol 6550--which can put you back $1K+ for the quad--or about half a dozen current productions that are more similar than different (JJ, Electro-Harmonix, Svetlana, Sovtek, Shuguang, etc.). So Roger's approach somewhat anticipated--in philosophy, but not in implementation--that of the H-cat; i.e., superb reproduction occurs (some would say demands) exacting control of balance and phase. This minimizes left/right and time smear, and results in the correct delivery of those higher-order harmonics and slight time delays that differentiate middle-C on a cello, from that on a high-school violin, from that of a Stradivarius. This is not what we do explicitly when we roll NOS, but perhaps some would say that implicitly this is what is happening, and that this is what separates the WE's and GEC's from the Sovteks.

Swampwalker, I understand that the buzz only happened after the Joule returned from repair, and I also assume from your answer to Bwhite that the Supratek does not do this with other amps, e.g. the Berning.

If part of a circuitry has a weak ground--for example, the return (ground) connection on an interconnect or RCA socket--then this can cause the signal to "find ground"--i.e., induce a current over dielectrics--in other parts and induce buzzing in tranformers.

Once the Joule and Supratek are connected via interconencts they are essentially a single circuit--and you are getting noise in both power supplies.

My guess--and this is simply a guess--is that either the process of connecting and disconnecting interconnects has created an intermitant short in one of them, or shipping may have caused some minor weakness in one of the many internal ground paths in the Joule. Because every component is different, it is coincidential that connecting the Yamaha C2A "curcuitry" doesn't induce errant current flows, but connecting the Supratek's does.

Try: 1) swapping a few interconnects; 2) inspecting, flexing, and testing them for continuity with a voltmeter; and/or 3) opening the Joule and looking for weak solder joint.

From the pics it looks like two KT-88s per channel, for a total of four. I own a Music Reference RM-200, which generates 100+ Watts also using two KT-88's per channel.