Preamp Deal of the Century

National Union vs RCA vs Ken-Rad 7193 tubes.

Since I have converted my Chenin to 7193s, I have been evaluating the different brands of 7193s available (in addition to enjoying the great sound!). Let me say that they are all excellent tubes, but there are some subtle differences between them, both in sound and in construction. All have black, relatively flat plates, with small boxes in the center.

National Union: The NUs have the smallest bottle of the three 7193s, and the getter is not visible from the exterior of the tubes. They have a round top and bottom mica. These were the first 7193s I ever heard, and they sound very good indeed. These are silky smooth, with a rich midrange. They are a little rolled off on the extremes compared to the other two tubes, but it is a not a huge difference.

RCA: The RCAs have a larger bottle than the NUs, with a bottom getter and round top and bottom mica. They have more extended highs and lows than the NUs, with fuller bass and a little more detail on top. Not quite as smooth as the NUs, and not quite as warm in the midrange.

Ken-Rad: The biggest bottle of the three, slightly larger than the RCA, with bottom getter and non-round top and bottom mica (looks like a round mica with a section cut out in each quadrant). The best bass of the three - the impact of kick drums is sensational, and bass lines can be felt and heard in great detail. The highs are nice and airy, with very good detail, and the midrange is very sweet as well.

So overall, in my opinion, I would rank the 7193s as follows:

Ken-Rad: best overall - it has everything

National Union: smoothest and warmest sounding, but a little less top and bottom than the others

RCA: Similar to the Ken-Rad, but not quite as smooth in the highs.

I've been listening to the Ken-Rad 7193s in my Chenin for about a month and one half now, and I decided to try an experiment last night. After listening to a few songs with the 7193s in place, I switched back to my RCA grey glass 6SN7s for comparison.
The difference was quite startling! The sound I used to think was very warm and full (the RCA 6SN7s) now sounded quite constricted and flat, compared to the 7193s - they just have so much "air" and sparkle at the top end that the 6SN7s just can't match.
It was back to the 7193s in very short order for me! I don't think I'll be repeating that experiment any time soon.

I just received most of the parts to do the 7193 conversion to my Cortese. I still need to get the wire. I will keep you posted.

Has anyone compared any of the Supratek preamp model against the Cary SLP 05 preamp ? If yes, lease share your experience. Thanks.

Tim

Picked up a pair of NOS Tung-Sol 5881 (6L6WGB) tubes for $25.00 at an antique radio swap meet this weekend. They have light brown bases and look to be 1950s vintage. The seller said they tested new, and they looked perfect, so I went for it. I've seen these online for $210.00/pair, and I know they are very popular with the guitar guys, but I figured I'd give them a whirl as regulators for my Chenin.

Verdict: They are an improvement over the stock Sovtek "5881" regulator tubes, providing a fuller midrange and slightly tighter bass, with no noticable ill effects. They are definitely a good match with the 7193 linestage tubes. I don't think I would pay $210 for them, but for $25 they are a nice upgrade. I was thinking of selling them at a profit when I picked them up, but I think they are staying put in my Chenin. My rectifier is a NOS GE 5AR4 (the one with the copper sides).