Preamp Deal of the Century

very interesting. now that supratek is defunct, i wondered how long it would take before modifications to the circuit started being proposed. while i am naturally intrigued by this, i don't think i'll mess with my dual cabernet if for no other reason than the sheer terror that would befall me frying the preamp.

I understand, Kg. Even though I thoroughly studied the circuit and went over the mod dozens of times in my head before I did it, I still had quite a bit of anxiety when I pushed in the power button. Happily, there was no factory smoke released.

Hi Gang. Hey...Kudos to Ait for his post on the 7193 conversion. Well thought out and very well written.

Kgturner. While the conversion is certainly do-able.... I rather doubt you would reap much of a benefit[if any] from this conversion anyway. The job of the 6sn7 in the circuit of your Dual was chosen for a very different role.
That said: And trust me here KG [as this is a simple a no-brainer move] Swap out the 6sn7's in your Dual for a pair of old stock Kenrad VT-231's [the black glass versions] The quality of bass reproduction from the Kenrad is simply majestic, and unmatched by any other tube in the 6sn7 family.

Just to clarify, no holes need to be drilled in the preamp! I was asked this question in an off-line email, so I thought I should post a clarification. I specifically designed this mod to make the fewest possible changes to my precious Chenin (they don't make these any more, ya know!), especially irreversible changes such as hole drilling. The wires from the top caps go into the tube base of the adapter and connect to two of the tube base pins, which then make the appropriate connections with the Chenin's internal wiring through the Chenin's 6SN7 tube socket. The ONLY mod to the preamp itself is to move the two output wires from the connections for triode II to the connections for triode I.

I just finished an extended listening session, and a few things stood out with the NU 7193s.

The highs are extraordinarily detailed and sparklingly clear. They might be fatiguing if it wasn't for the total lack of glare - these tubes are clean, clean, clean. This probably has to do with the anode and grid connections being through the top caps, a design feature which was adopted specifically to improve high frequency performance in radio frequency applications, according to several on-line sources I have found.

The mids are very natural and warm, but not as warm as those from the RCA Grey Glass 6SN7s, which some might consider overdone. The harmonies on the Beatles "Love" CD were thrilling.

The bass is about the same as I had with the 6SN7s, maybe a bit tighter. I'm looking forward to receiving the Ken-Rad 7193s (which should have been here by now...) as Ken-Rads are well-known for their prodigious bass. Stay tuned.